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OREGON STATE UNIVERSITYAGRICULTURAL EXPERIMENT STATION

St 1. ,n .uIL n SB 683November 2000

41 )UNT:

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JNVOICE #:

Additional copies of this publication available for $10.00:

Publications OrdersExtension and Station CommunicationsOregon State University422 Kerr AdministrationCorvallis, OR 9733 1-2119

Phone: 541-737-2513fax: 541-737-0817e-mail Puborders @orst.edu

Cover Photo: Individually fed beef cows at the USDA/ARS Northern Great Basin ExperimentalRange (NGBER) locaed about 35 miles west of Burns, Oregon. (Photo by Tim DelCurto)

Trade-name products and services are mentioned as illustrations only. This does not mean that theOregon State University Agricultural Experiment Station either endorses these products andservices or intends to discriminate against products and services not mentioned.

Oregon State UniversityAgricultural Experiment Station

Station Bulletin 683November2000

Strategic Supplementation of Beef CattleConsuming Low-Quality Roughagesin the Western United States

A Western Regional Research Publication of the Western Coordinating Committee 110Improving Ruminant Use of Forages in Sustainable Production Systems for the Western United States

Participating Western Region State Agricultural Experiment Stations

University of AlaskaAmerican Samoa Community CollegeUniversity of ArizonaUniversity of CaliforniaColorado State UniversityUniversity of Guam

University of HawaiiUniversity of IdahoCollege of MicronesiaMontana State UniversityUniversity of NevadaNew Mexico State University

Community College of NorthernMañana Islands

Oregon State UniversityUtah State UniversityWashington State UniversityUniversity of Wyoming

In cooperation withUSDA-ARS, Fort Keogh LARRL, Miles City, MT 59301; Texas Agricultural Experiment Station,Texas A&M University, San Angelo, TX 76901; and Rosepine Research Station, Louisiana State University,Rosepine, LA 70659

AUTHORS

Callan Ackerman, Department of Animal Sciences, Oregon State University, Corvallis, OR 97331

Ray P. Ansotegui, Department of Animal & Range Sciences, Montana State University,Bozeman, MT 59717

Jan P. Bowman, Department of Animal & Range, Montana State University, Bozeman, MT 59717

Tim DelCurto, Associate Professor, Eastern Oregon Agricultural Research Center, Union Station,Oregon State University, Union, OR 97883

Elaine E. Grings, USDA-ARS, Fort Keogh LARRL, Miles City, MT 59301

Pat G. Hatfield, Department of Animal & Range Sciences, Montana State University,Bozeman, MT 59717

Bret W. Hess, Department of Animal Science, University of Wyoming, Laramie, WY 82071

James Ed Huston, Animal Nutritionist, Texas Agricultural Experiment Station, Texas A&M University,San Angelo, TX 76901

Kenneth C. Olson, Associate Professor, Department of Animal, Dairy, and Veterinary Sciences,Utah State University, Logan, UT 84322-48 15.

John A. Paterson, Department of Animal & Range Sciences, Montana State University,Bozeman, MT 59717

Mark K. Petersen, Department of Range & Animal Sciences, New Mexico State University,Las Cruces, NM 88003

Larry R. Rittenhouse, Rangeland Ecosystem Science Department, Colorado State University,Fort Collins, CO 80523

David W. Sanson, Rosepine Research Station, Louisiana State University, Rosepine, LA 70659

Connie K. Swenson, Research Nutritionist, Zinpro Corp., Eden Prairie, MN 55344

Chapter 1. Introduction

SUPPLEMENTAL FEEDING OF RANGE LIVESTOCK: AN INTRODUCTION

Sustainable livestock production utilizingrangelands requires knowledge of thenutritional value of available forage andexperience with the probable responses bylivestock to the quality and availability of thatforage. These predicted responses arecompared to the desired productivity of thegrazing animal. If the predicted animalresponse is less than the desired productivity,then supplementation is considered.Supplementation research that started over 50years ago has attempted to develop a predictivetool that could be used by ranchers. However,industry and nutritionists are still unclear onwhat type, amount, and duration of supplementis needed for optimum profitability of grazinganimals.

Under extensive livestock management,systems comprised of management expertise,fences, water, and white salt, livestock givebirth and reproduce during the periods ofavailable green vegetation. These animals gothrough cycles, within a year, of using storedbody nutrients and then replacing thosenutrients. Not every animal is reproductivelysuccessful each year. Those that do reproduceevery year are suited to their nutritionalenvironment because they can synchronizetheir high nutritional demands andreplenishment of body energy reserves to occurwhen abundant, high quality forage isavailable. This particular scenario, althoughlow cost, may not optimize profitability.Therefore, to enhance profitability, ournutritional management is planned around anoptimal marketing scheme, and the nutritional

Mark K. PetersenDepartment of Range & Animal Sciences

New Mexico State University, Las Cruces, NM 88003

Pat G. HatfieldDepartment of Animal & Range Sciences

Montana State University, Bozeman, MT 59717

3

environment is altered (by supplementation) tobest fit the marketing decisions.In range operations, the ranch is the energy ornutrient supply for the livestock. Energy is theconstituent of the diet that is needed in thelargest quantity. When range and grazingmanagement are planned simultaneously withanimal energy needs, dietary energy rarelyshould be supplemented. As long as livestockcan consume herbage to their appetite everyday, the livestock manager has made thegreatest and usually lowest cost impact onnutrient intake. At times when energy demandby the animal exceeds energy intake (snowcover or other environmental effects thatreduce forage availability, cold stress, lactation,and late pregnancy), deposited body energyreserves can be used to meet the animal'sneeds.

Protein is the nutrient needed in the secondgreatest amount. To utilize forage energyefficiently, there must be a balance withprotein. In most situations when livestock aregrazing or browsing dormant, non-greenherbage, the balance of protein to energy isinsufficient. Under these conditions, a proteinsupplement can improve forage digestibilityand intake. By meeting the nutrient needs ofthe microorganisms that degrade fiber in therumen, the net effect is more protein andenergy available to the animal. Sometimesmicrobial protein is not sufficient to meet theanimal's needs. Then, a protein can be fed tocomplement the protein derived by themicrobes. In this situation, bypass protein maybe used effectively to meet requirements duringlactation, weight loss, antibody production, or

wool growth. The challenge at this point is thedelivery of a protein supplement. Thefollowing questions may need to be resolved:How much protein? What sources will be usedeconomically? Should it be fed as a 20, 32, or40 percent crude protein (CP) supplement? Fedfor what period of time? Should it be fed everyday, every other day, or once a week? Can itbe fed as a liquid, cubes, cake, or in blocks?Should younger or thinner animals receivemore per day or for a longer period? We needto know what is the least amount ofsupplement, fed in the simplest method, whichwill allow for accomplishment of productiongoals.

Minerals and vitamins are required in the thirdand fourth largest quantity. They are importantfor animal structure, enhancing metabolism andimmune function, and maintaining electrolytebalance, and are found in all parts of the body.Some can be stored and used over long periods,while others are needed on a daily basis. Themost common method to supplement mineralsand vitamins is through salt mineral mixes,using livestock's attraction to salt as amechanism to entice mineral consumption.Because of yearly variation and normalproduction fluctuation, it is difficult for mostranchers to assess the effectiveness of anysupplementation program, especially withminerals, in any one year.

Any nutrient not consumed in the necessaryamount or balance to other nutrientscompromises animal metabolism andproduction. It is important to establish whichnutrient is most limiting or out of balance andsupply that nutrient first. Observation of cattleand forage conditions, along with experience,can be used to assess the first limiting nutrient.Other methods that have been used with littleor limited success are: clipped forage samplesalong with a forage analysis, analysis of bloodurea nitrogen concentration or collecting fecalsamples, and using prediction equations todetermine limiting nutrients. Especially withsheep, clipped forage samples are not indicativeof the quality of the diet that animals arecapable of consuming. In fact, the limitation in

4

the diet may change between years, so that insome years an energy supplement is mosteffective, some years a protein, and in otheryears no supplement is the best choice for thelowest unit cost of production. Even within arange livestock operation that has not changedgenetic potential of the grazing animal,supplement needs, if any (type, quantity, time,duration, etc.), can change from year to yearbecause of changes such as environmentalconditions that impact forage availability andquality, and factors that effect body conditionof animals as they enter traditionalsupplementation periods.

Additional burdens to range animal nutritionistsare the seasonal changes in forage quality andavailability. With good moisture and moderatetemperatures, forages are succulent and containhigh nutrient density. As the seasonprogresses, forages become coarser, drier, andlower in nutrient density. By mid-winter, thesedormant forages contain 30 percent of theiroriginal protein, are 50 percent lower indigestibility, and almost all high quality solublenutrients have been leached away. As foragequality changes during the year, livestockprotein requirements double, and energyrequirements increase 50 percent. This createsa situation in which important criteria forsupplementation decisions are constantlychanging.

Finally, evaluation of the success of anutritional management plan is difficult. Onthe ranch, it is important to have good recordsand then to make comparisons over years todetermine the optimal nutritional managementplan for improved productivity andprofitability. Even better, but more difficult, isto use ranch-based experiments and assessdifferent nutritional programs. The complexityof supplementation decisions (i.e., forageconditions, forage availability, animalcondition, that which might be the lowest costmanagement plan in one year may negativelyimpact replacement rates long term) can bebeyond the typical ranch manager's experience.Decision aids are what is needed, to take intoaccount all of the factors simultaneously, to

produce choices with the highest probability oflong-term success.

As production costs rise and societal views offood safety and confinement meat productionbecome more critical, meat production fromextensive grazing operations may be positionedwell to increase market share of meatconsumption in the 21st century. However,meat and protein production rapidly isbecoming a world market. U.S. producers,even for domestic consumption, must becompetitive with other meat producingcountries. Nutritional costs represent both thehighest variable cost in the form of feeds andthe highest fixed cost in the form of landpurchases. The key to the lowest unit cost ofproduction is grazing the reproductive femaleas long as possible. Strategic supplementationof the grazing female needs to balance low unitcost of production with long term reproductiveperformance to yield a sustainable productionsystem.

Cattle grazing at EOARC Hall Ranch

5

The goal of this publication is to expand on ascheme called Strategic Supplementation. Byusing this process, livestock are supplementedonly during the most effective period, with theminimum potent amount, and in a practicaldelivery system.

Hopefully, this publication will assist rangelivestock managers and nutritionists in makingthese supplementation decisions.

CHARACTERISTICS AND CHALLENGES OF SUSTAINABLE BEEFPRODUCTION IN THE WESTERN U.S.

Tim DelCurtoEastern Oregon Agricultural Research Center, Union Station

Oregon State University, Union, OR 97883,

David BohnertEastern Oregon Agricultural Research Center, Burns Station

Oregon State University, Burns, OR 97883,

Callan AckermanDepartment of Animal Sciences

Oregon State University, Corvallis, OR 97331

Introduction

Beef cattle producers in the Western U.S. arefaced with the dilemmas of maintainingeconomic viability during times of low marketvalues and, more recently, increased publiccriticism of beef product quality and industrycompatibility with the environment. Unlikeother meat animal industries, such as swine andpoultry, the beef industry in the western UnitedStates is very dynamic. It must adaptconstantly to changing arid environments andsubsequent effects on forage quality andquantity, and associated relationships with beefcattle nutritional requirements. As a result, theWestern beef cattle industry is very extensive,with optimal production being a function of theresources each ranching unit has available andhow successfully the manager can match thetype of cow and (or) production expectations tothose resources. Successful beef producers arenot necessarily the ones who wean the heaviestcalves, obtain 95 percent conception, orprovide the most optimal winter nutrition.Instead, the successful producers are dynamicand adaptive to economic and public pressuresthat challenge the industry.

Rangeland Forage Resources

The western United States has several uniquegeographic features that shape and influence

6

the beef cattle industry. Much of the land areafits the general classification of "rangeland";hence, it is not suitable for tillage due to aridenvironments, shallow/rocky soils, highelevations, and short growing seasons. Fromarid rangelands in the Northern Great Basin(cold desert) to arid rangelands in southernNew Mexico, ranchers are faced with limitedforage resources and challenging nutritionalcalendars. Arid/high elevation rangelands alsoare characterized by dynamic, highly variableclimates that change drastically from season toseason and year to year. For example, thecrude protein (CP) content of diets selected bycattle in the Northern Great Basin differsdramatically across seasons and years (Figure1).

24

Figure 1 Crude proterr content of diets selected by cattle grazieg NorthernGreat Basin native rangelends. Crude protein requremerts (NRC, 1984) areindicated fora high milking (20 lbs/day), average milking (10 lbs/day) andnonlectating gestating beef cow (1 1CX) Ibs).

20

-.-- 1990-e- 1991

19935 16C00

12

2C)

8

4April May June July August Septenter

The extremes in CP content in this data set are,in turn, related to wide ranges in crop yearprecipitation averaging 158, 246, 231, and 524mm for 1990, 1991, 1992, and 1993,respectively (40-year average = 277 mm) Theextreme fluctuations in precipitation also hadsignificant affects on forage availability, with1990 to 1992 averaging 240 kg/ha, whereas1993 forage availability was 580 kg/ha. Thebeef manager must be aware of these changesand be able to adapt to wide ranges in foragequality and quantity.

The dynamic nature of arid/high elevationrangelands, in terms of forage quality, forageavailability, and environmental extremes (snowcover, precipitation, temperature, etc.) results inseasonal cattle body weight and conditionchanges that mimic those observed with foragequality and availability. This has beenillustrated in many winter grazingsupplementation studies. DelCurto andcoworkers (1991) supplemented cows grazingsagebrush steppe rangelands during the winterwith graded levels of alfalfa and reporteddramatic differences in cow weight and bodycondition change compared across years(Figure 2). Specifically, the magnitude ofresponse was dramatically different betweenconsecutive years due to observed changes inforage quality, forage availability, andenvironmental stress imposed on the grazingcattle. Likewise, other researchers in thewestern U.S. have indicated variable resultswhen supplementing free-ranging beef cattleconsuming stockpiled forage. While this doesnot adequately describe all the considerationsneeded for supplementing grazing livestock, itdoes point out some of the complexities inachieving optimal response to supplementationstrategies in arid environments. Obviously,further research is needed to describe theinteraction of environment, foragequality/quantity, and livestock nutrientdemands so that optimal use of the forageresources, minimal use of supplements, andacceptable levels of beef cattle production canbe obtained.

7

150

100

50

0

-50

-100

o -150-200

0 14 28 42 56 70 84 98 11

Figure 2. Body weight changes of beef cows winter grazingintermountain rangelands and supplemented with alfalfa (1990 and199fl.

Winter Feed Needs

Perhaps the greatest challenge to Western beefproducers relates to the need for supplementalfeed. Seasonal deficiencies of nutrients(protein/energy) are usually extreme in arid andhigh elevation rangelands. Consequently,producers dependent on rangeland forageresources must develop strategies to maximizethe use of the forage resources and minimizesupplemental inputs while maintainingacceptable levels of beef cattle production.Likewise, high-elevation and high latitude beefcattle operations are likely to have significantperiods of snow accumulation, whichnecessitate feeding of harvested forages. In thePacific Northwest and Intermountain West,many producers feed 1,500 to 3,000 kg of hayto their mature cows during the winter feedingperiod. This represents costs of $75 to $150per cow per year and may be greater than50 percent of the input costs per cow per year.Obviously, our ability to compete with otherregions of North America may depend on howeffectively we can reduce winter-feed costs, yetstill maintain acceptable levels of beef cattleproduction.

The success of producers in the western UnitedStates may depend on their ability to findeconomical alternatives to winter-feeding ofhay, such as stockpiled forages and cropresidues. However, like dormant range forages,stockpiled forage and crop residues are low-

1990 ContI x 19903 arara

T---1991 Control 1991 3kgafalfa -

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quality roughages that require nutritional inputsfor optimal use. What follows is a generaldiscussion of potential management strategiesthat may offer economic advantages to Westernrange livestock producers. Many scenarios orstrategies may not be appropriate for yourenvironment or production goals. Instead, mostof the following information should beconsidered potential management alternativesthat may offer economic advantages bydecreasing input costs per cow.

Management to Reduce Nutritional Inputsand Costs

One of the most fundamental objectives ofeconomically sustainable livestock productionis to not provide nutritional inputs such asharvested feeds and (or) supplements unless itis necessary. Therefore, the first goal of amanager should be to match the biologicalcycle and nutritional demands of the cowherdwith the forage resources available.

When is the best time to calve? One of themost fundamental management decisions thathas profound effects on beef cattle nutritionalrequirements is calving date. Calving date setsthe biological cycle, which, in turn, determinesthe nutritional cycle of the cowherd and theassociated relationship to ranch resources. TheWestern beef cattle industry is dominated byspring-calving cattle. In addition, time ofcalving generally has been related to the "55days to grass" philosophy. This traditionalmanagement strategy has gained popularity fora variety of reasons. First, gestation length inbeef cattle is approximately 284 days.Therefore, if your cowherd calvesapproximately 55 days before the onset ofgreen forage, the cows will be exposed togreen, highly nutritious forage forapproximately 25 days before they mustconceive to stay on a 365-day calving interval.In a sense, the 25 days of high quality forage isa natural "flushing" mechanism that normallyprompts a cow to begin cycling, provided shewas in adequate body condition initially.Obviously, if your goal is to match the cows'

8

nutritional requirements with available foragequality, as a producer you might coincidecalving with the onset of green forage (Mclnnisand Vavra, 1997). However, the "55 days tograss" philosophy has another advantage: thecalf. A typical beef calf does not develop afully functioning rumen until approximately 90

to 120 days of age. This normally coincideswith the time a cow has passed its peaklactation period (day 70 to 90); and, as a result,calf performance will depend largely on thequality of available forage. Thus, a calf bornMarch 1 effectively utilizes the high qualityforage available in June. In contrast, a calfborn May 1 does not utilize forage resourceseffectively until August, when forage quality isnormally low in the Intermountain region.Because of the vast difference in calf nutritionfrom day 90 to weaning, the earlier born calfwill have weaning weight advantages thatgreatly outweigh the 60-day difference in age.If higher weaning weights are a measure ofeconomic importance (you market calves in thefall), then the "55 days to grass" philosophymay be the best approach.

Are weaning weights really important? Thebeef cattle industry in the United States hasseen dramatic changes in productionefficiencies over the last 30 years. Inparticular, weaning weights have increasedfrom approximately 400 pounds in 1967 togreater than 600 pounds in 1997. The increasein weaning weights is related to increased useof continental breeds, greater selection forgrowth traits, and general improvements inmanagement efficiency. Heavier weaningweights could increase the potential for profit ifthe producer's goal is to market calves in thespring. This scenario would only be true if theincreased income of heavier weaning weightsoutweighs the added cost of attaining thatincrease in weight.

However, the increase in weaning weights is animprovement in production efficiency that hassome indirect problems. First, the targetslaughter weight of market cattle has notchanged dramatically during this period. As aresult, the opportunities to put on post-weaning

weight have become limited with the heavierweaning weight cattle. For example, if aspring-calving cow/calf producer weans hiscattle in late October at 600 pounds, he/shemay choose to sell in the fall market or retaincalves over the winter feeding period.However, because of the bigger calves, his/heroptions are reduced. With only marginal gainsof ito 1.5 pounds per head per day, thisproducer will come out of the winter feedingperiod (120 to 150 days) with 700 to 800 poundyearlings. The opportunities to place theseanimals on spring grass have now become veryrestricted. To fit market standards, yearlingsneed to be placed in the feedlot (avg. 90 days)with an expected gain of 300 to 350 pounds inorder to meet a target end weight of 1,200 to1,300 pounds. Therefore, heavy-weaning,spring-born calves have limited opportunitiesas stocker cattle on grass markets.

Another change in the beef cattle industry inrecent years is the trend toward retainedownership and (or) branded markets. Thesechanges indirectly have led producers toreevaluate weaning weight goals because ofopportunities to capture weight gains onyearlings and the need to provide cattle atfinished weights on a yearly time frame. Forproducers who wish to retain ownership ofcattle after weaning, weaning weight takes onless significance. In fact, these producers arethe ones who should consider calving datesstrongly. If a producer wishes to decrease costsper cow, moving the calving date tosynchronize cow nutrient demands withrange/pasture forage quality may effectivelyreduce costs associated with supplementingcows during nutrient deficiencies. Weaningweight advantages are reduced, but theproducer has more opportunities to capturegains in the stocker, backgrounding, andfinishing phases.

Preparing the Cow-Herd for the WinterPeriod

Because the winter period represents a time ofhigh feed costs for beef cow-calf production,

9

management strategies should emphasizedecreasing the inputs. Getting your cowherd ingood fleshy condition going into the winterperiod should be a year-round managementgoal. Obviously, this involves monitoring yourrange and (or) pasture forage conditions withparticular attention to the quantity and qualityof late summer and early fall forage (Figure 1).Forage resources in the Pacific Northwest areinfluenced strongly by the Mediterraneanclimate and, as a result, are dominated by coolseason forages. The majority of precipitationcomes in the winter months, while summers arerelatively dry. As a result, forage quality andquantity may be limited and, at the very least,highly variable during late summer and fall.

A manager should monitor cow body conditionand calf performance in late summer. Whencows start losing body condition and (or) calfperformance begins to decline, the producershould consider nutritional managementstrategies to optimize cow condition going intothe winter period. A cow in good condition (5or better) going into the winter period is easierto feed and can lose some body conditionwithout adversely effecting subsequent calvingand rebreeding potential.

Early weaning as a management tool.

Traditionally, beef producers in the Great Basinregion have weaned calves at approximately 7months of age, which is usually late October orNovember for spring-calving herds. However,gains of both calves and cows are often poor bylate August, particularly during years of poorforage quality/quantity. Early removal ofcalves allows the producer to provide themhigher quality sources of feed and potentiallygreater gains at a similar cost to later weaning.The cows can be left on the range and, due tothe removal of the nutrient demands oflactation, do well on range forage during thefall; without a suckling calf, the cows willcome into winter in better condition. Improvedbody condition, in turn, translates into a cowthat is easier to maintain during the winterperiod and has a higher chance of breeding

back and maintaining a 365-thy calvinginterval.

Figure 3 presents some early weaning datafrom the Eastern Oregon Agricultural ResearchCenter herd (Turner and DelCurto, 1991).Early-weaned calves were removed from theirdams on September 12 and put on meadowaftermath and regrowth supplemented with 2pounds of barley and 1 pound of cottonseedmeal. Late-weaned calves remained on rangewith their dams until October 12 and then weremanaged with the early-weaned calves.Beginning on November 12, all calves wereprovided meadow hay, 2 pounds of barley, and1 pound of cottonseed meal daily throughoutthe winter. Early-weaned calves gained moreweight than late-weaned calves by 20 poundsfrom September 12 to October 12 despite goingthrough the stress of weaning and adjusting tonew feed. During the next period, October 12to November 12, the early-weaned calves out-gained late-weaned calves by an additional 31pounds and were now 51 pounds heavier. Late-weaned calves compensated somewhat over theremainder of the winter, but they were still 24pounds lighter on April 12.

A number of factors must be considered whendeciding if early weaning is appropriate. First,forage quality must be limiting to the point thatcalf gain will be reduced and cows are likely tolose body condition from late August to theOctober or November weaning date. If foragequality and (or) quantity are not limiting, thereis really no advantage to early weaning. Thereal advantage of early weaning is to improvethe weight and body condition of the cowsfrom late summer to the beginning of the.winter feeding period. In addition, theproducer must provide adequateforage/nutrition to the early-weaned calf. Forproducers with limited nutritional optionsduring the late summer and fall period,however, early weaning may provide analternative that allows greater efficiency in themanagement of mature cows' body condition.In turn, improved body condition of cattlegoing into the winter period facilitates reduced

10

supplemental feed requirements during thewinter period.

w 510e 490

470gh 450

t, 430

410

b 390

370

.4 Early weaned

I,

', eanin

Late weaned

anifl

August September October November

Month

Figure 3. Influence of weaning date on calf weights (Turner andDelCurto, 1991).

Alternative Nutritional ManagementStrategies

Rake-bunch hay. The Eastern OregonAgricultural Research Center conductedapproximately 10 years of research evaluatingrake-bunch hay as an alternative to traditionalwinter management. With this system, hay iscut, then raked into small piles (80 to 120pounds) with a bunch rake, and left in the field.The forage then is strip-grazed, using NewZealand type electric fences, throughout thewinter. A general summary of 10 years of datademonstrated that cows wintered on rake-bunchhay came out of the winter period in bettercondition than traditionally fed cows and didnot require supplements or additional hay.Likewise, conception rates, calving interval,weaning weights, and attrition rates were equalbetween traditionally fed and treatment groups.In addition, the costs of winter feeding rake-bunch hay has been $30 to $40 less per headthan the traditional feeding of harvested haydue, in part, to reduced harvest and feedingcosts. For additional information relative torake-bunch hay feeding, please refer to Turner(1987) and Turner and DelCurto (1991).

Winter grazing. Another alternative totraditional winter-feeding is winter grazing of"stockpiled" forage. To use this alternative

effectively in the Intermountain region, theproducer must defer grazing of irrigated pastureor native range to the fall or winter months.The range forage base will be dormant and, as aresult, is likely to need some level ofsupplementation depending on quality ofselected diets, body condition status of maturecows, and stage of gestation. Brandyberry etal. 1994 offers more thorough discussions ofwinter grazing are available.

Similar to rake-bunch hay, winter grazing maydecrease winter feed cost by $20 to $30 percow during mild to average years (Bates et al.,1990). To winter graze pastures or nativerangelands effectively, the land area must havenumerous attributes. First, the producer musthave access to the animals to accommodatesupplementation programs. In addition, watermust be available throughout the fall or wintergrazing period, although cows can utilize snoweffectively. However, the grazing area must berelatively free of snow accumulation duringmost years.

Indirect benefits of winter grazing relate to theincreased management opportunities oftraditional hay meadows for spring and earlysummer grazing. In addition, fall and wintergrazing is an alternative use of nativerangelands that may provide some significantadvantages. First, deferment of grazing to thefall and winter months minimizes potentialdamage to native plants that are sensitive toearly season defoliation, such as bluebunchwheatgrass (Agropyron spicatum Pursh;Mueggler, 1975; McLean and Wikeem, 1985);Idaho fescue (Festuca idahoensis Elmer;Mueggler, 1975; Jaindl et al., 1994); andThurber needlegrass (Stipa thurberiana Piper;Ganskopp, 1998). Second, the grazing ofnonlactating-gestating cows is distributed betterover the grazing area, demonstrating greaterdistance traveled from water, better use ofslopes, and more uniform use of the grazed area(Hedrick Ct al., 1968).

Grass seed residues. Another alternative totraditional winter management is the use ofgrass seed residues produced as a by-product of

11

Oregon's Grass Seed Industry. Currently,Oregon's Grass Seed Industry produces over 1million tons of crop residues. While only50 percent of these residues appear to be aviable livestock feed resource due to qualityand (or) anti-quality factors, there are a numberof reasons producers should consider thesefeeds as winter alternatives. First, many of thegrass species are perennial forages (Kentuckybluegrass, tall fescue, perennial ryegrass,bentgrass, etc.) and, as a result, aresubstantially better than annual cereal grainstraws. Second, burning, which traditionallywas used as a tool to sanitize fields and removeresidues, has been eliminated as the primarytool for grass seed producers. As a result, thereis a critical need to find an effective use forthese residues. Third, the Japanese exportmarket has become "soft" in recent years,making delivery of grass seed residues to theeastern portions of Oregon more economicallyviable.

In most cases, grass seed residues should not beconsidered a complete feed for winteringmature beef cows. Instead, the nutritive qualityof grass seed straws should be tested andsupplements formulated to meet nutritionalrequirements while maximizing the use of thelow-quality roughage. A more thorough reviewof grass seed residues and associatedsupplementation are available fromChamberlain and DelCurto (1991) and Turneret al. (1995). Currently, grass seed straw isbeing delivered to Eastern Oregon forapproximately $40 to $50 per ton. Theeconomic practicality of this feed resourceshould not only be compared with the costsassociated with meadow hay production, butalso with other potential benefits. First, feedinggrass straw frees up meadows traditionally usedto produce hay for grazing and (or) other uses.Second, grass seed residues represent a cleanfeed with limited weeds, with the exception ofthe seeds from the residue itself. Onintroduced/improved pastures, germination ofperennial seeds from perennial ryegrass, tallfescue and (or) bluegrass may be beneficial towinter-feeding sites. Third, feeding residues onwinter-feed grounds or traditional hay

meadows represents an increase in nutrientsadded to the site. Decreased fertilizer costs andimproved organic matter of the soil may resultfrom long-term feeding of grass seed residues.

Strategic supplementation. Managementpractices such as water development, salting,fencing, fertilization, and herding have beensuccessful in improving forage and pastureutilization by cattle (Cook, 1966; Kauffmanand Krueger, 1984; Bailey and Rittenhouse,1989). However, implementation has beenminimal over extensive locations andenvironments, primarily due to impracticalityand (or) costs involved. In contrast, strategicsupplementation has potential as a reasonableeconomic alternative to the aforementionedpractices.

Recent work has demonstrated that strategicplacement of supplement can lure cattleeffectively to ungrazed or under-utilized areas,thereby improving animal disbursement andpasture utilization, even in moderate anddifficult terrain (Bailey and Welling, 1999).These workers used dehydrated molassessupplement blocks as a management tool toalter cattle location and pasture utilization.They reported that supplementation increasedgrass utilization (within 200 m of supplementlocation) compared with non-supplementedareas by approximately 24 and 12 percent formoderate and difficult terrain, respectively.

Intensive management of native flood meadow.Most native flood meadows are privatelyowned, They often produce up to 10 timesmore forage compared with sagebrush-bunchgrass range (Angell, 1997) due toincreased water availability in the spring andearly summer from annual runoff of highelevation snow pack. In general, 1 ha of nativeflood meadow frees 10 ha or more of typicalsagebrush-bunchgrass range (Angell, 1997).

Traditional management of native floodmeadows in the Intermountain West (1,618,800ha; Gomm, 1979) involves haying in thesummer and grazing aftermath and regrowth inthe fall. However, control of water is minimal

12

and results in uncontrolled flooding (durationand amount). This normally prevents hayinguntil the forage has become mature. As aresult, hay quality is low, with CPconcentration often less than 7 percent and totaldigestible nutrients (TDN) less than 50 percent.In addition, cattle are brought to the meadowsfrom summer range in order to wean spring-born calves, winter the cowherd, and calve. Asa result, beef cattle routinely spend half of theyear on native flood meadows grazing residualforage or being fed hay harvested from themeadows. Consequently, many traditional beefcattle producers work within a managementsystem that has developed around the annualproduction cycle of native hay meadows.

These highly productive meadows provideseveral alternatives to traditional hay-onlymanagement. Cattle can gain in excess of 2pounds per day while grazing these meadows inthe spring and summer, with nosupplementation (Figure 4; Angell, 1997). Thisprovides the benefit of added pounds of gain aswell as deferring native range for late-seasonuse. In addition, these cattle are in bettercondition going into the winter and require lessfeed to maintain acceptable performance. Asecond option is using meadow regrowth,harvest aftermath, or stockpiled forage, inconjunction with an early-weaning program, asa forage resource for calves. A third option isearly-season grazing along with haying or late-season grazing.

Irrigated pasture. Irrigated pasture can be anexcellent buffer when range forage is limited inquantity and (or) quality. With controlledirrigation and proper management, thesepastures can offer high quality forage that canbe grazed yearlong, harvested multiple timesfor hay, or used in combinations of late and (or)early season grazing in addition to hayproduction. Research has shown that growingcattle can gain well on irrigated pasture, andcows and spring-born calves can be held onpasture in early spring to allow deferment ofnative range for late-season use and (or)development of plant species sensitive to early-season defoliation (Gomm, 1979). In addition,

irrigated pasture can be used as a supplementalforage source in drought situations. Irrigatedpasture can provide all of the managementalternatives described previously for nativeflood meadow, while improving the ability tomanage forage production, quality, andavailability.

2.00

1.75 -

C)

: 1.25

I.< 0.75 -

0.50 -

0.25

0.00 -f I

May June July

L Meacbw

Sabrush-bunchgrss

Figure 4. Expected daily gains of yearling cattle grazing either native flood meadowor sagebrush-bunchgrass range from May through August at the EasternOregon Agriculture Research Center (adapted from Angell, 1997).

Rumen fermentation modifiers. Rumenfermentation modifiers alter microbialfermentation in the rumen. Their purpose is toincrease the quantity of energy obtained fromfeed consumed by cattle. Products currentlyapproved for use in beef cattle consuming aforage diet include Rumensin® (monensin),Bovatec® (lasalocid), and GAINPRO(bambermycin). Each of these productscommonly is used to improve the feedefficiency and (or) weight gain of cattle onpasture. Gain of steers and heifers on pasturehas been improved by approximately 0.15 to0.20 pounds per head daily when one of theseproducts is included in a supplement. Inaddition, research at the Eastern OregonAgricultural Research Center has shown thatRumensin can improve winter beef cowperformance and (or) reduce winter feed needs(Turner et al., 1977; Turner et al., 1980). Cowsfed a diet of meadow hay plus 200 mg of

r

13

monensin had daily gains 0.2 pounds higherthan cows fed meadow hay alone. In studieswhere cow body weights were kept equalbetween control cows receiving meadow hayand cows receiving meadow hay plusmonensin, hay savings of up to 13 percent wererealized. These rumen fermentation modifiers

represent another managementtool for improving cow conditionor reducing feed requirementswhile maintaining cow conditionthrough the winter feedingperiod. Each of the productsmentioned has various labelclaims and are available indifferent forms of feed.However, the cattle producerwho uses these products has theresponsibility of using themproperly. This includes (1) using

Ai it for its intended purpose, (2)following the feeding guidelinesand any warning statement on thelabel, and (3) storing the feedproperly.

Alternative Management -- A "Systems"Approach

Beef producers in the Intermountain West arein urgent need of management practices thatprovide sustainable alternatives to traditionalmanagement and are dynamic enough toprovide options if government regulationsdecrease or eliminate public grazing allotments.When developing these strategies, animalscientists and beef cattle producers mustcontend with the public's preconceived notionthat any livestock grazing is bad for theenvironment and (or) wildlife. In reality, theeffect of livestock grazing on an ecosystemdepends on a number of variables, includinggrazing or browsing intensity, the evolutionaryhistory of the ecosystem, and the opportunityfor regrowth (Hobbs, 1996). Therefore, thecontinued use of public and private lands bylivestock producers will depend on the abilityof animal and range scientists, Extensionspecialists, and producers to formulate

management systems that help overcome thestigma that livestock grazing is not asustainable use. This point is illustrated in asurvey by Coppock and Birkenfeld (1999). In apoll of 340 livestock producers in Utah rangingfrom large operators to part time ranchers or"hobbyists," they reported that the greatestperceived threats to the respondent's livelihoodwere reduced access to public and private landsand lack of applied information and technologyfor production and management. Thisdemonstrates the need for alternative methodsand technologies that can provide managementoptions for Intennountain beef producers. Inaddition, these technologies must be practicaland presented in an understandable format thatencourages implementation by cattle producers.

The typical beef cattle operation in theIntermountain West utilizes three broadcategories of land. These are sagebrush-bunchgrass communities, coniferous forests,and native flood meadows. Traditionalmanagement entails using sagebrush-bunchgrass range for spring and summergrazing and coniferous forests when sagebrush-bunchgrass range is mature and dry. Cattle aremoved to native flood meadows in the fall towean calves, winter the cowherd, and calve.Cattle are able to consume a limited quantity ofmeadow regrowth and harvest aftermath, andthen they are fed hay harvested from themeadows earlier in the summer. Two possiblealternative management scenarios using a"whole system" approach are listed below.

One possible management alternative would beto graze native flood meadows in the springand early summer followed by early weaning.The early-weaned calves would be placed onirrigated pasture and the cows moved to maturenative range and strategically supplementedthrough late winter. Calves would be sold ormoved to a feedlot when the irrigated pasturewas no longer able to sustain grazing(dependent on calf prices and available feedresources). Cows would be brought back to thenative flood meadows approximately 1 to 2months before calving and fed hay or rake-bunch until they are moved again to mature

14

native range in late summer. A portion ofnative flood meadow would be deferred fromgrazing in the spring and used for harvestinghay and rake-bunch. In addition, the irrigatedpasture would be harvested at least once priorto use by early-weaned calves. Care and propermanagement would be undertaken whengrazing late-season native range to ensure thatriparian areas are protected and not over-utilized. Harvested hay would be used asemergency forage for cows and (or) sold as asource of additional revenue.

Another potential "systems" approach would beto maintain all animals on native flood meadowyearlong. The meadows would be grazed in thespring and early summer followed by earlyweaning as described above. However, early-weaned calves would be placed on rake-bunchand supplemented, while the cows would beheld on native flood meadow that had beeneither mechanically harvested or grazed. Thecows would be allowed to consume any hay (orrake-bunch not used by the calves) harvestedduring the summer and then provided grassseed straw and supplemented to meet expectedproduction goals. Cows would be placed onnew forage as it became available in the spring.Straw would be purchased and delivered to theranch. Calf and meadow management wouldbe as described above.

Rapid changes in technology, marketingstrategies, and environmental concerns andregulation are challenging severely themanagerial abilities of many producers andthreatening their livelihood. The primarypurpose of this discussion is to prepare cattleproducers and managers for the changes thatare occurring in the beef industry and toprovide them with the ability to understand andrespond appropriately. We briefly haveoutlined two potential management scenarios;however, there are numerous others that can beused by Western beef cattle producers. Inaddition, no one scenario or strategy isappropriate for all producers. Each producermust evaluate his or her own enterprise anddecide which alternative(s) is most suitable.Using alternative management practices in a

"whole system" approach requires increasedfuture planning and adaptability in relation toanimal, forage, and land use. However, it willprovide economic sustainability and, thereby,help improve the future of beef production inthe West.

Summary

The ability of Western beef cattle producers tocompete effectively with other regions of NorthAmerica may depend on management strategiesthat emphasize profit margins rather thanweaning weights. The above information only"scratches the surface" of potential alternativemanagement strategies that may offer economicadvantages. Keep in mind, however, thatWestern beef cattle producers and resources aredynamic, and incorporation of any of thesestrategies must fit your production philosophy,production goals, and holistic ranchmanagement plan.

Many of the management strategies describedin this paper, as well as future opportunities forbeef production in the Pacific andIntermountain West, necessarily involve theuse of supplementation to utilize low-qualityfeed resources. Producers must evaluate whichsupplements are most economically viable intheir region, as well as which strategy best fitstheir needs, nutritional calendar, andmanagement style.

Literature Cited

Angel!, R. 1997. Mixing and matching:Grazing wet meadows and desert range.The sagebrush steppe: sustainableworking environments. Agric. Exp. Sta.Spec. Rep. 979. Oregon StateUniversity. pp. 14-21.

Bailey, D.W. and L.R. Rittenhouse. 1989.Management of cattle distribution.Rangelands. 11:159-161.

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Bailey, D.W. and R. Welling. 1999.Modification of cattle grazingdistribution with dehydrated molassessupplement. J. Range Manage. 52:575-582.

Bates, J.D., H.A. Turner, and F.W. Obermiller.1990. An assessment of cow winter-feeding regimes using a net energybased biophysical-economic simulationmodel. Proc. West. Sec., Amer. Soc.Anim. Sci. 41:137-140.

Brandyberry, S.D., T. DelCurto and R.A.Angell. 1994. Physical form andfrequency of alfalfa supplementation forbeef cattle winter grazing northernGreat Basin rangelands. Agric. Exp.Sta. Special Rep. 935. Oregon StateUniversity.

Chamberlain, D. and T. De!Curto. 1991. Useof grass seed residues as a winter-feedresource for beef cattle. Eastern OregonAgric. Res. Center Circ. of Info. No. 2.

Cook, C. 1966. Factors affecting utilization ofmountain slopes by cattle. J. RangeManage. 19:200-204.

Coppock, D.L., andA.H. Birkenfeld. 1999.Use of livestock and range managementpractices in Utah. J. Range Manage.52:7- 18.

DelCurto, T., R.A. Angell, R.K. Barton, J.A.Rose and S.C. Bennett. 1991. Alfalfasupplementation of beef cattle grazingwinter sagebrush-steppe range forage.Agric. Exp. Sta. Special Rep. 880.Oregon State University.

Ganskopp, D. 1998. Thurber needlegrass:Seasonal defoliation effects on foragequantity and quality. J. Range Manage.5 1:276-281.

Gomm, F.B. 1979. Irrigated pastures for rangelivestock. Agr. Exp. Sta. Tech. Bull.635. Oregon State University. 15 pp.

Hedrick, D.W., J.A. Young, J.A.B. McArthur,and R.F. Keniston. 1968. Effects offorest and grazing practices on mixedconiferous forests of northeasternOregon. Agr. Exp. Sta. Tech. Bull. 103.Oregon State University. 24 pp.

Hobbs, N.T. 1996. Modification ofecosystems by ungulates. J. Wildi.Manage. 60:695-713.

Jaindl, R.G., P. Doescher, R.F. Miller, and L.E.Eddleman. 1994. Persistence of Idahofescue on degraded rangelands:Adaptation to defoliation or tolerance.J. Range Manage. 47:54-59.

Kauffman, J.B., and W.C. Krueger. 1984.Livestock impacts on riparianecosystems and streamside managementimplications. A review. J. RangeManage. 37:430-438.

McLean, A. and S. Wikeem. 1985. Influenceof season and intensity of defoliation onbluebunch wheatgrass survival andvigor in British Columbia. J. RangeManage. 38:21-26.

Mclnnis, M.L. and M. Vavra. 1997. Diningout: Principles of range cattle nutrition.Oregon State University Agric. Exp.Sta. Spec. Rep. 979:7.

Mueggler, W.F. 1975. Rate and pattern ofvigor recovery in Idaho fescue andbluebunch wheatgrass. J. RangeManage. 28:198-204.

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NRC. 1984. Nutrient Requirements of BeefCattle (6th Ed.). National AcademyPress, Washington, DC.

Turner, B., F. Conklin, T. Cross, T. DelCurtoand D. Carroll. 1995. FeedingOregon's grass straw to livestock:Economic and nutritionalconsiderations. Agric. Exp. Sta. SpecialRep. 952. Oregon State University.

Turner, H.A. 1987. Utilizing rake-bunch hayfor wintering mature cows. Research inBeef Cattle Management. Agric. Exp.Sta. Spec. Rep. 801. Oregon StateUniversity. pp. 1-7.

Turner, H.A., and T. DelCurto. 1991.Nutritional and managerialconsiderations for range beef cattleproduction. In: Veterinary Clinics ofNorth America. John Maas (ed.). W.B. Saunders, Co. pp. 95-126.

Turner, H.A., R.J. Raleigh, D.C. Young. 1977.Effect of monensin on feed efficiencyfor maintaining gestating mature cowswintered on meadow hay. J. Anim. Sci44:338.

Turner, H.A., R.J. Raleigh, and D.C. Young.1980. Effect of various levels ofmonensin on efficiency and productionof beef cows. J. Anim. Sci. 50:385.

Chapter 2. Protein/Energy and Physical FormConsiderations

ENERGY/PROTEIN SUPPLEMENTATION CONSIDERATIONS FORGRAZING RUMINANTS

Jan P. BowmanDepartment of Animal & Range

Montana State University, Bozeman, MT 59717

David W. SansonRosepine Research Station

Louisiana State University, Rosepine, LA 70659

Introduction

Dormant range forage is usually high in fiberand may be deficient in both protein andenergy, especially for cows during lategestation and lactation (Krysl et aL, 1987b;Krysl and Hess, 1993). Limited forage quantityor quality may necessitate supplemental feed tomaintain reproductive efficiency or to achievedesired levels of production. Unfortunately,when cattle consuming low-quality forages aregiven traditional concentrate supplements thatcontain high amounts of non-structuralcarbohydrates (NSC) such as cereal grains,forage intake and digestibility often aredepressed (Chase and Hibberd, 1987; Cordes etal., 1988; Sanson and Clanton, 1989; Sanson etal., 1990). However, supplementation withfibrous by-product feedstuffs that contain highlevels of structural carbohydrates, such assoybean hulls and wheat middlings (Chan et al.,1991; Horn et al., 1995), or with higher qualityforages, such as alfalfa (Bowman and Asplund,1988; DelCurto et al., 1990a; DelCurto et al.,1990b; Atwell et al., 1991), has been shown toincrease intake and utilization of low-qualityforages. This review examines the effects ofenergy supplements containing starch or fiberon forage intake and utilization by grazingruminants.

Substitution for Forage vs. EnhancingForage Quality

The purpose of supplementation of ruminantsconsuming forages is to make up for limited

19

forage quantity, where supplement substitutesfor forage; or to make up for nutrientdeficiencies, where supplement enhances foragequality. Ensminger et al. (1990) definedsupplementation as adding feedstuffs to the dietto improve the value of the base feed. By thisnarrow definition, many of the feedstuffs thatare fed with forages are not true supplements,because they do not improve the utilization ofthe forage. A broader definition of supplementswould be feedstuffs added to the base forage toprovide nutrients required to support the desiredlevel of production. This definition ofsupplementation often applies when the desiredlevel of production is significantly above thelevel provided by the base forage. Although thedifference between these two definitions mayappear trivial, it becomes important whensupplements provide a more economical sourceof energy than forages. It is also importantwhen substitution for forages is desirable, aswhen forage availability is limiting or foragesupplies need to be stretched.

In the early part of this century, Armsby andFries (1918) reported that readily fermentablecarbohydrates decreased crude fiber digestion;and Morrison (1940) summarized literature inhis text that indicated molasses or sugardecreased forage digestibility. Other earlysupplementation work by Fontenot et al. (1955)and Campbell et al. (1969) indicated thatsupplements high in NSC interfered with fiberdigestibility. In contrast, Johnson et al. (1962)reported that feeding soybean hulls with poor-quality timothy hay increased organic matter(OM), cellulose, and crude fiber digestibility

compared to values predicted from digestibilityobtained when either feedstuff was fed alone.Beginning with these early supplementationstudies, research indicated that not all energysupplements were equal in their effects onforage utilization.

Carbohydrate Composition of EnergySupplements

Although protein supplements provide energyand may stimulate additional energy intake,generally the term "energy supplement" refersto either cereal grains or by-products of thegrain milling industry. Energy supplements canbe classified into those high in NSC (starchesand sugars) or those high in structuralcarbohydrates (cellulose and hemicellulose).Examples of energy supplements containinghigh levels of NSC are corn, barley, andsorghum grains, and molasses-based liquids orblocks. Examples of energy supplementscontaining high levels of structuralcarbohydrates are soybean hulls, wheatmiddlings, beet pulp, and alfalfa hay. It isessential to understand the carbohydratecomposition of energy supplements fed withforages, because the type of carbohydrate has amajor effect on forage utilization.

Supplementation of forage diets withconcentrates containing NSC often decreasesfiber digestion and forage intake (Tamminga,1993). Starch has been shown to have anegative effect on fiber digestion (Mould et al.,1984; Firkins et al., 1991). This depression infiber digestion may result from the effects oflow ruminal pH from increasing volatile fattyacid production on the growth of fibrolyticbacteria (Hiltner and Dehority, 1983;Tamminga and Van Vuuren, 1988), from anincrease in lag time for fiber digestion due topreferential use of NSC by fibrolytic bacteria(Mertens and Loften, 1980; Hoover, 1986), orfrom competition for nutrients betweenfibrolytic and amylolytic microorganisms(Mackie et al., 1978; Hoover, 1986). Whenfiber digestion is depressed, passage rate may

20

be decreased as well, reducing forage intake(Robinson et al., 1987; Uden, 1988).

By-products of concentrate feeds generallycontain more fiber and less starch than theparent feedstuffs. This results in a lower NSCto structural carbohydrate ratio. In addition, by-product fiber or structural carbohydrate ishighly digestible (Highfill et al., 1987; Hsu etal., 1987; Anderson Ct aL, 1988b; Nakamuraand Owens, 1989) compared with fiber in mostforages. As an example, soybean hulls are lowin ferulic and para-coumaric acids, non-corelignin phenolics that form covalentcrosslinkages between lignin andhemicelluloses and thereby reduce digestibilityof the structural carbohydrate fraction (Garlebet al., 1988).

Supplementation of forage diets with by-product feeds usually results in less negativeeffects on fiber digestion than supplementationwith the original grains (Cordes et al., 1988;Garleb et al., 1988). High levels of structuralcarbohydrates compared to NSC may increasenumbers or activity of cellulolytic bacteria(Silva and Orskov, 1985). By-productconcentrates with a high fiber content tend tostabilize rumen fermentation by maintaining amore constant pH, and prevent the negativeassociative effects of concentrates on foragedigestion (Tamminga, 1993). In fact, positiveassociative effects have resulted fromsupplementation with soybean hulls to all-forage diets (Johnson et al., 1962; Hintz et al.,1964; Sudweeks, 1977).

Associative Effects of Feeds

Associative effects of feeds usually are ignoredwhen balancing diets for ruminants, and it isassumed that each feed will contribute a givenamount of nutrients without interfering with theutilization of the other feeds. This approachdoes not account for the effects that thesupplemental feed may have on fermentation ofthe basal forage. Associative effects can benegative or positive.

A positive associative effect resulting fromsupplementation is seen when supplementalprotein is provided to animals consumingmature, low-protein forages. Many studieshave reported increases in low-quality forageintake and (or) digestibility when supplementalprotein was fed (McCollum and Galyean, 1985;Krysl et al., 1987a; Stokes et al., 1988; Sansonet al., 1990). Steers fed mature, low-proteinforage had increased ruminal ammoniathroughout a 24-h period when a rumen-degradable protein supplement was fed (Sansonet al., 1990). These steers responded tosupplemental protein with an increase in dietand forage dry matter intake (DM1). A22 percent increase in DM1 by cattle (Elliott,1 967a) and an 11 percent increase in DM1 bysheep (Elliott, 196Th) were reported whenpeanut meal was fed as a supplement. Otherstudies have shown increases in intake ofmature, low-protein forages by both sheep(Smith and Warren, 1986; Krysl et al., 1987a;Matejovsky and Sanson, 1995) and cattle(McCollum and Galyean, 1985; Smith andWarren, 1986) when rumen-degradable proteinwas fed. Dry matter digestibility of low-qualityforages also has been increased with proteinsupplementation (Church and Santos, 1981;DelCurto et al., 1990a; Sanson et al., 1990;Gaebe et al., 1994; Matejovsky and Sanson,1995). The above cited increases in forageintake and digestibility resulted in greater intakeof digestible nutrients than would be expectedfrom the nutrient content of the forage and thesupplement individually.

A negative associative effect occurs when thesupplement suppresses intake or digestibility ofthe forage so that the intake of digestiblenutrients is less than would be expected fromthe forage and supplement separately. Negativeassociative effects have been reported whencattle and sheep consuming mature forageswere supplemented with corn (Chase andHibberd, 1987; Sanson and Clanton, 1989;Sanson et al., 1990).

Moore et al. (1995) estimated associativeeffects between forages and supplements in 113mixed diets for which digestibility was reported

21

and observed metabolizable energy (ME;Mcal/kg OM) could be estimated. Theexpected ME was estimated using forage andsupplement intakes and ME concentrations. Ifthe observed ME of the mixed diet was greaterthan expected, a positive associative effectoccurred; and if observed ME was less thanexpected, a negative associative effect occurred.Both positive and negative associative effectswere seen when supplement OM intake wasless than 0.8 percent of body weight (BW), butonly negative associative effects were seenwhen supplement intake was greater than0.8 percent BW. Positive associative effectsdue to feeding supplements were seen primarilywhen forages were "unbalanced" (had adeficiency of protein relative to energy) or hada digestible OM (DOM) to CP ratio of greaterthan 7.

Attempts have been made to estimate forageDM digestibility when supplements are fed byassigning a constant digestibility value (usuallythe total digestible nutrients [TDN] value) tothe supplement, and then correcting the fecaloutput for the undigested supplement.. Thisapproach assumes that all of the negativeassociative effect that occurs from feeding asupplement is on the forage, and disregards thepossibility that the digestibility of both forageand supplement may be affected. Decreases inestimated hay DM digestibility of low-qualityforages have been seen with sheep (Sanson,1993; Matejovsky and Sanson, 1995) and cattle(Sanson and Clanton, 1989; Sanson et al., 1990)supplemented with increasing levels of corn.Chase and Hibberd (1987) reported a cubicdecrease in estimated hay DM digestibilitywhen steers consuming a low-quality hay weresupplemented with increasing levels of corn.These researchers concluded that a smallamount of corn supplement may have little orno effect on hay digestion, whereas higherlevels have a negative associative effect.

Level of Supplementation

Limited amounts of NSC may stimulate fiberdigestion by increasing microbial activity andattachment to fibrous digesta (Demeyer, 1981;Hiltner and Dehority, 1983); however,increasing amounts of NSC usually depressforage digestion and intake.

Chase and Hibberd (1987) reported that forageand total diet DM1 by cows fed mature, low-protein native grass hay decreased linearly aslevel of supplemental corn increased from 0 to0.78 percent BW. These supplements werebalanced for similar N intake from thesupplements, but not for similar Ndegradability. A cubic response was seen inforage neutral detergent fiber (NDF)digestibility to level of corn supplementation.Little effect on forage NDF digestibility wasseen at the first level of corn supplementation;however, a large decrease in digestibilityoccurred between the first and second level ofcorn, and then only a small decrease betweenthe second and third level of corn. Dietdigestible DM1 also responded in a cubicfashion, with intake by cows receiving thehighest level of supplementationbeing4 percent below that of cows receiving nosupplemental corn. Sanson and Clanton (1989)reported linear decreases in intake anddigestibility when steers consuming a low-quality meadow hay were supplemented withincreasing levels of corn (0, 2.5, 5, or 7.5 g/kgBW). Sanson et al. (1990) reported quadraticresponses in intake and digestibility by steersconsuming a low-protein meadow hay andunsupplemented or supplemented with protein,or protein plus 2.5 or 5 g/kg BW corn.

Vanzant et al. (1990) supplemented steersconsuming bluestem forage (6.1 percent CP)with increasing levels of grain sorghum (0, 1.5,3.1, or 6.2 g/kg BW). Forage intake anddigestible NDF intakes were not affected byincreasing level of supplement, whereas totaldiet DM1 was increased linearly by increasinglevel of supplementation. In contrast,Pordomingo et al. (1991) reported a lineardecrease in forage OM intake by steers grazing

22

blue grama summer rangeland andsupplemented with 0, 2, 4, or 6 g/kg BW ofcorn, with no effect on total OM intake ordigestible OM intake. When steers were fed amedium-quality bromegrass hay (9.9 percentCP; 56.2 percent dry matter digestion [DMD])and supplemented with 6 g/kg BW corn orbarley (Carey Ct al., 1993), diet intake was notaffected by supplementation, although forageintake by steers receiving supplements waslower than steers receiving only a proteinsupplement. Paisley et al. (1994) fed steersnative meadow hay (9 percent CP) and 0, 2.5,or 5 g/kg BW of either corn or barley. Forageintake was depressed quadratically by bothsupplements, whereas diet DM1 and digestibleDM1 were not affected. Sanson (1993) reportedlambs consuming low-quality hay andsupplemented with increasing levels of cornexhibited a decrease in forage intake when thelevel of corn reached 0.75 percent BW. Studieswith steers fed low-quality forage andsupplemented with increasing levels of corndemonstrated a decrease in forage intake whenthe level of corn reached 0.5 percent BW(Chase and Hibberd, 1987; Sanson and Clanton,1989; Sanson et al., 1990). These data indicatethat the response in forage intake to level ofcorn supplementation differs between cattle andsheep, with sheep able to consume higher levelsof supplemental corn before forage intake isnegatively affected.

In the above studies with low-protein, matureforages, supplements containing low levels ofNSC tended to affect forage utilizationpositively, whereas supplements containinghigh levels of NSC had small to large negativeaffects, depending on the amount of NSC fed.It appeared that supplements with high levels ofNSC, such as feed grains, have minimalnegative effects on forage utilization when fedat or less than 0.25 percent BW. At levelsabove 0.25 percent BW, negative effects weremuch larger.

We used data from 116 comparisons in theliterature that estimated forage DM1 with andwithout supplementation to evaluate the effectsof level and composition of supplement on

change in forage intake. Supplement DM1 as%BW, supplement %CP, forage %CP, forageDM1 as %BW without supplementation, forageDM1 as %BW with supplementation,composition of the supplements, and the changein forage DM1 as %BW due to supplementationwere estimated from the individual researchstudies. Data from the Cornell net carbohydrateand protein system (Sniffen et al., 1992) wereused to estimate supplement NSC intake as%BW, supplement starch intake as %BW,supplement %NSC, supplement %carbohydrate, supplement carbohydrate intakeas %BW, supplement sugar intake as %BW,and supplement CP intake as %BW.Correlations were made between the change inforage DM1 (%BW) and all of the forage andsupplement characteristics. Results of thecorrelation analysis are presented in Table 1.The two characteristics that had the greatestindividual relationship with the change inforage DM1 were forage %CP and supplementstarch intake as %BW. Using stepwiseregression analysis, forage %CP andsupplement starch intake as %BW explained65 percent of the variation in the change inforage DM1 (P = 0.000 1) and resulted in theprediction equation: Y = 0.95 - 0.11 (forage%CP) - 0.62 (supplement starch intake, %BW).This equation predicts that increasing forage CPcontent and increasing supplemental starchintake would reduce any positive effectsupplementation had on the change in forageDM1. Figure 1 represents this predictionequation, plotting the change in forage DM1versus forage CP content, when defined levelsof supplemental starch are fed ranging from0.15 to 0.75 percent BW. For a 1,200 lb cow,0.1 percent BW starch intake represents 1.8 lbsupplemental corn, and 0.5 percent BW starchintake represents 9.2 lb supplemental corn.Figure 1 indicates that 0.1 percent BW starchcan be fed with forages containing up to8 percent CP without a negative effect onforage intake. However, 0.1 percent BW starchhas a negative effect on forage intake when fedwith forages containing greater than 8 percent

23

Table 1. Correlations between changes in forage DM1with supplementation, forage, and supplementcharacteristics, as calculated for 116corn arisons in the literature.

CP. A level of 0.5 percent BW supplemental starch canbe fed with forages containing6 percent CP or less without negative effects on forageintake.

Substitution Rate

Substitution rate is defined as the change inforage intake in kg DM per kg supplement DMfed. A positive substitution rate indicates thatforage intake was reduced by supplement intake"substituting" for forage. A negativesubstitution rate indicates that forage intake wasincreased by supplementation.

Goetsch et al. (1991) reviewed 18 studies withsteers fed bermudagrass and supplemented withcorn at levels from 0 to 1 percent of BW andreported that for each kg of corn, hay DM1decreased by 0.46 kg (substitution rate of 0.46).These hays varied in CP from 8 to 12 percent.In contrast, lambs consuming a medium-qualitynative hay (10 percent CP) and supplementedwith corn had a substitution rate of -0.17,whereas lambs consuming a high-quality hay(14 percent CP) exhibited a substitution rate of -0.02 (Matejovsky and Sanson, 1995). Widevariations in the substitution of supplement forforage have been reported by others. Moore etal. (1995) calculated the substitution rate for135 comparisons between forage intake aloneand when supplement was fed, and found littlerelationship between substitution rate andforage characteristics or level of supplementintake.

Item Change in forage DM1, %BWForage CP, % -0.66Supplernent characteristicsIntake, %BW -0.47CP,% 0.33NSC, % -0.27Carbohydrate, %t -0.39NSC intake, %BW -0.56Starch intake, %BW -0.66Carbohydrate intake, %BW -0.53Sugar intake, %BW -0.41

Jones et al. (1988) reported intakes of a warm-season forage (bermudagrass) by steerssupplemented with 0.48 percent BW of cornwere higher than a cool-season forage(orchardgrass), although calculated substitutionrates were similar (0.42 and 0.48 forbermudagrass and orchardgrass, respectively).Pordomingo et al. (1991) observed a lineardecrease in forage intake with steers grazingsummer blue grama rangeland andsupplemented with corn. Calculatedsubstitution rates were -0.95, 1.25, and 1.3 forsteers fed 0.2, 0.4, and 0.6 percent BW of corn,respectively. This forage had a mean CP of10.5 percent and in vetro dry matter digestion(IVDMD) of 62 percent. Carey et al. (1993)reported a substitution rate of 0.56 for steers feda medium-quality forage and supplementedwith corn, barley, or beet pilp; whereas, Paisleyet al. (1994) observed a substitution rate of 1 forcorn and 0.72 for barley with steers fed amedium-quality forage. Chase and Hibberd(1987) reported a substitution rate of 0.56 forsteers fed low-quality forage. Dairy cowsgrazing perennial ryegrass-white cloverpastures (17 to 22.8 percent CP) andsupplemented with 4 or 8 kg of barley, hadsubstitution rates of 0.64 (Opatpatanakit Ct al.,1993). The Australian Standard Committee onAgriculture (1990) reported a substitution rateof 1 for high digestibility supplements fed tocows grazing high-quality forage, and asubstitution rate of 0.6 for low digestibilitysupplements. Aliden (1981) indicated thatforage availability affects substitution rate, withsubstitution rate increasing linearly with forageavailability below 1,500 kg DM/ha.

Broster and Thomas (1981) indicated thatsubstitution rate can be influenced by foragecharacteristics, level and type of concentrate,and physiological state of the animal. Manyresearchers found substitution rate increasedwith increasing level of supplement (Phipps etal., 1988; Faverdin et al., 1991); however,others reported no effect on substitution rate oflevel of supplementation (Gordon, 1984;Opatpatanakit et al., 1993). Supplementscontaining high levels of NSC have been shownto have higher substitution rates than

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supplements containing lower levels ofNSC(Meijs, 1986; Faverdin et al., 1991).

Jarrige et al. (1986) reported that substitutionrates vary with forage quality and fill value.These authors presented data that suggest thatas fill value increased (forage qualitydecreased), the substitution rate decreased, orbecame more negative. The concept appearsvalid in general; however, when fill values andsubstitution rates were estimated with sheep,the substitution rates were from 0.2 to 0.4(Sanson et al., unpublished data), compared toobserved substitution rates of 0.8 to 1 withmedium- to high-quality forages presented byJarrige et al. (1986). This points out problemswith assigning one substitution rate for allconcentrates and all animals.

We made calculations of substitution rate for116 observations in the literature whereestimates of change in forage DM1 withsupplementation were given. These data arepresented in Figure 2, and a strong relationship(R2=0.51;P=0.0001;Y-1.77+0.24X)was found between substitution rate and foragepercent CP. Substitution rate was zero whenforage CP was equal to 7.4 percent, averaged -0.83 for forages below 7.4 percent CP, averaged0.5 for forages between 7.4 and 12 percent CP,and averaged 2.0 for forages above 12 percentCP. This means that each unit of supplementresulted in a 0.78-unit decrease in forage DM1when forage CP was between 7.4 and12 percent, and resulted in a 2-unit decrease inforage DM1 when forage CP was above12 percent. A 0.83-unit increase in forage DM1resulted when forage was below 7.4 percent CP.Using stepwise regression, substitution rate wasbest predicted (R2 = 0.60; P 0.000 1) by DM1of the forage without supplementation (DMIF),forage CP%, (FCP), supplement CP% (SCP),and supplement starch intake as %BW(STIBW), resulting in the following predictionequation: Y = -1.69 + 0.34(DMIF) + O.18(FCP)- 0.02(SCP) + 0.32(STIBW). The substitutionrate increased (became more positive, orsupplement had a larger depressing effect onforage DM1) as DM1 of forage withoutsupplementation, forage CP%, and supplement

starch intake (%BW) increased. Substitutionrate decreased (became more negative, orsupplement had a less depressing effect onforage DM1) as supplement CP percentincreased. As demonstrated in the abovecalculation of substitution rate, and suggestedby Jarrige et al. (1986), the substitution rate of asupplement varies with the characteristics of theforage and the supplement.

Non-Structural Carbohydrate Supplements

Differences may exist in source and amount ofNSC, as barley has been shown to have agreater negative effect on fiber digestioncompared with corn (DePeters and Taylor,1985; McCarthy et al., 1989; Herrera-Saldanaand Huber, 1989). Others have reported nodifferences between supplemental grain sourceswhen fed at similar DM levels (Vanzant et al.,1990). Galloway et al. (1993) reported nodifference in digestible OM intake by steers fedbermudagrass hay and supplemented with1 percent BW of ground corn, whole corn,ground grain sorghum, or ground wheat.However, gain was greater for grazing steerssupplemented with ground corn, whole corn, orground sorghum grain, than for thosesupplemented with barley or wheat.Fredrickson et al. (1993) reported nodifferences in prairie hay intake when steerswere supplemented with 0.25 percent BWstarch from barley, corn, grain sorghum, orwheat.

The effect of NSC supplementation on (NDF)digestibility has varied. Chase and Hibberd(1987) reported a decrease in NDF digestion aslevel of corn fed to steers consuming low-quality hay increased. Neutral detergent fiberdigestion was decreased by cornsupplementation in sheep (Sanson, 1993) andcattle (Sanson Ct al., 1990) consuming low-quality forage. Sanson and Clanton (1989)reported a decrease in disappearance of NDFfrom nylon bags when steers consuming low-quality forage were supplemented with corn.Carey et al. (1993) reported a decrease in NDFdigestion by steers receiving a medium-quality

25

forage and either corn or barley supplement,whereas Paisley et al. (1994) reported no effectof supplemental corn or barley on NDFdigestion by steers consuming a medium-quality forage. Krysl et al. (1989) reported noeffect on in situ NDF disappearance whensteers grazing medium-quality rangeland weresupplemented with steam-flaked sorghum grain.Vanzant et al. (1990) reported no effect ofsupplemental grain sorghum on NDF digestionby steers consuming early-growing season,bluestem forage; whereas, Jones et al. (1988)reported a decrease in NDF digestion of steersconsuming either orchardgrass or bermudagrassand supplemented with 0.5 percent BW of corn.Galloway et al. (1991) observed no differencesin NDF digestion when Holstein steers were fed0.5 percent BW corn and bermudagrass, yetNDF digestion decreased when ryegrass-wheathay and 0.5 percent BW corn was fed. Withbermudagrass, NDF digestion averaged10.5 percent lower than ryegrass-wheat NDFdigestion. These data indicate a large variationin the effect of cereal grain supplementation ondigestion of the NDF fraction by sheep andcattle.

By-product Supplements

Some by-products of the milling industry offerfeeds that are low in NSC and contain structuralcarbohydrates that have high digestibility.Supplementation with fibrous by-productfeedstuffs, such as soybean hulls and wheatmiddlings, has been shown to increase intakeand utilization of low-quality forages by cattle(Chan etal., 1991; Hornet al., 1995; ørskov,1991). Wheat middlings supplements increasedforage intake and fiber digestibility when fed tobeef cattle consuming dormant range forage(Sunvold et al., 1991). Martin and Hibberd(1990) reported a quadratic decrease in hay OMintake, a quadratic increase in total diet OMintake, and a linear increase in digestible OMintake and NDF digestibility when cowsconsuming low-quality grass hay weresupplemented with increasing levels of soybeanhulls. It should be noted that when evaluatingthe effects of supplements high in degradable

fiber on diet NDF digestibility, the digestibilityvalue includes the digestibility of thesupplement as well as the forage. In this case,actual forage NDF digestibility may havedecreased, since it would be expected that thedigestibility of the NDF fraction of soybeanhulls would be higher than the forage. Sanson(1993) reported diet DM digestibility decreasedlinearly when lambs consuming mature crestedwheatgrass hay were supplemented withincreasing levels of corn, whereassupplementation with increasing levels of beetpulp did not affect diet DM digestibility.Supplementation with increasing levels of corncaused a linear decrease in NDF digestibility,while NDF digestibility increased linearly withincreasing levels of beet pulp supplementation.

Anderson et al. (1 988a) reported steers andheifers grazing smooth brome pastures andheifers grazing corn stalks had similar gainswhen supplemented with soybean hulls or anequal amount of supplemental DM from cornand gained more than unsupplemented animals.Marston et al. (1992) supplemented gestatingcows grazing dormant native prairie with 0.64kg of protein from supplements containingdifferent combinations of soybean hulls andsoybean meal. Cows receiving a supplementcontaining high levels of soybean hullsconsumed less forage but gained more weightthan cows receiving a supplement low insoybean hulls.

Forage NDF intake by steers increased withincreasing soybean hull supplementation, butdecreased when corn was supplemented(Anderson et al., 1988b). Average daily gainand feed conversion were similar in growingcalves when they were fed forage dietssupplemented with soybean hulls or corn(Anderson et al., 1 988b). Stocker cattle grazingwheat pasture had improved gains when fed asoybean hull/wheat middling supplementcompared with a corn supplement (Horn et al.,1995).

Ovenell et al. (1989) and Cox et al. (1989)reported experiments where fall- and spring-calving cows grazing dormant native prairie

26

received supplements containing 0.54 kg CPand 0, 0.36, 1, or 2.2 kg wheat middlings.Spring-calving cows had increased weight gainwith increasing level of wheat middlings in thesupplement. In contrast, level of wheatmiddlings in the supplement did not affectweight change of fall-calving cows (lactating);all lost weight during the supplementationperiod. Any additional energy supplied by thesupplement may have increased milkproduction at the expense of cow weight in thefall-calving cows.

Kunide et al. (1995) compared supplements ofcorn, wheat middlings, and soybean hulls fed at0.5 or 1 percent BW to growing steersconsuming high-quality bermudagrass hay.Gain, forage intake and NDF digestibility weresimilar for all three supplements when fed at0.5 percent BW. However, when supplementswere fed at approximately 1 percent BW, cattlefed corn had lower gains, forage intake anddigestibility than those fed soybean hulls.Cattle fed wheat middlings at 1 percent BW hadgains intermediate to those fed corn or soybeanhulls.

Cows grazing winter range wereunsupplemented or supplemented with soybeanhulls/soybean meal, wheat middlings, orbarley/soybean meal fed to supply equalamounts of DM and CP, but increasing levels ofNSC (Surber et al., 1996). Intake anddigestibility of forage and total diet DM, OM,and NDF decreased linearly with increasinglevel of NSC. The lowest NSC supplement,soybean hulls/soybean meal, increased total dietintake of CP. Cow BW change respondedquadratically to increasing level of NSC, withthe most weight being lost by unsupplementedcows, and those receiving the highest level ofNSC, the barley/soybean meal supplement.Carboxymethylcellulase activity of particle-associated microbes attached to forage extrusaruminally incubated in nylon bags decreasedlinearly with increasing level of NSCsupplementation (Figure 3). Increasing levelsof NSC reduced cellulolytic activity of ruminalmicrobes, resulting in decreased foragedigestibility and intake.

High-quality Forage Supplements

High-quality forages also have application assupplements for mature low-quality forages.Judkins et al. (1987) reported that heifersgrazing dormant rangeland responded similarlyto supplementation with alfalfa hay when fed atan equal level of CP as they did tosupplementation with cottonseed meal. High-quality grass forage also can be used as asupplement. Villalobos et al. (1992) reportedcows grazing dormant native range andsupplemented with 0.31 kg of protein fromeither high-quality meadow hay or soybeanmeal gained more weight than cows receivingno supplement.

Bowman and Asplund (1988) reported a9 percent increase in DM1 and a 60 percentincrease in ADG when lambs consuming low-quality Caucasian bluestem hay weresupplemented with alfalfa hay. When beefcows grazing dormant range forage weresupplemented with soybean meal/sorghumgrain, alfalfa hay, or dehydrated alfalfa pellets,forage intake was increased over cows notgiven supplement (DelCurto et al., 1990b).Cows fed alfalfa hay or dehydrated alfalfapellets had a greater digestible DM1 thanunsupplemented cows or those supplementedwith soybean meal/milo Forage OM intakeand digestibility were increased when steersconsuming low-quality range forage were fedsupplemental alfalfa at 0.5 percent BW(Lintzenich et al., 1995).

Castrillo et al. (1995) supplemented sheepconsuming barley straw with increasing levelsof meadow grass hay, beet pulp, or barley.Straw intake decreased linearly with increasinglevel of all three supplements, but no effect ofsupplement type was seen.

Vanzant and Cochran (1994) fed beef cowsgrazing low-quality forage increasing levels ofsupplemental alfalfa hay (0.48, 0.72, or0.96 percent BW) during the winter, and foundquadratic responses in digestible DM1 andestimated ME intake. Cows fed the highestlevel of alfalfa supplement weaned the heaviest

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calves, had the shortest interval to conception,and lost the least amount of weight and bodycondition.

Forage Quality

In general, forage quality and nutritive valuedecrease with physiological maturity or growthstage due to increases in the proportion ofcellulose, hemicellulose, and lignin, anddecreases in CP and NSC content (Nelson andMoser, 1994). The digestibility of structuralcarbohydrate also decreases as forages mature(Gordon et al., 1983; Nelson, 1988; Shaver etal., 1988). When native meadow forages wereharvested at two different maturities, thedigestibility of structural carbohydrates was45 percent for the late-cut or mature foragecompared to 60 percent for the early-cut forage(Sanson et al., unpublished).

The decrease in forage digestion seen with NSCsupplementation becomes more severe asforage quality declines (Doyle, 1987; Beever etal., 1988). However, the depression of forageDM1 by NSC supplementation is greater withhigh-quality forages than with low-qualityforages (Jarrige et al., 1986; Minson, 1990).

In a review of the effects of chemical andphysical composition of forage on intake,Minson (1982) reported that intake of foragescontaining greater than 8 percent CP was notincreased by supplemental protein. Forage ordiet DM1 was not increased by a rumen-degradable protein supplement when lambsconsumed a medium- or high-quality forage(Matejovsky and Sanson, 1995).

Moore et al. (1995) reported a relationshipbetween the change in forage DM1 whensupplements were fed and the ratio of DOM toCP in the forage. When DOM:CP was less than7 (a balance between energy and protein), thechange in forage DM1 with supplementationwas always negative. When DOM:CP wasgreater than 12 (very unbalanced for proteinrelative to energy), the change in forage DM1was always positive, with all types and levels of

supplements increasing forage intake. WhenDOM:CP was between 7 and 12 (deficient inprotein relative to energy) the changes in forageDM1 were both positive and negative, withincreases in forage intake occurring with lowintakes of supplement, and decreases in forageintake occurring with high intakes ofsupplement.

Forage quality alters the effects thatsupplements have on forage utilization. Lambsconsuming low-quality forage responded to aprotein supplement with increased forage DM1,but increasing levels of corn supplementdecreased forage DM1 (Matejovsky and Sanson,1995). Total diet DM1 was decreased whencorn intake was above 0.5 percent BW. Incontrast, total diet DM1 by lambs fed medium-or high-quality forage was not affected by levelof corn supplementation, and forage DM1decreased linearly, implying a 1:1 substitutionof the corn for the forage. Diet digestibilityincreased linearly with increasing supplementlevel for lambs fed all three forage types.

In a study to evaluate the interaction of foragequality and level of supplementation, lambswere fed low- (5.2 percent CP, 44 percentDMD), medium- (10.2 percent CP, 58 percentDMD) or high-quality (14.2 percent CP,58 percent DMD) hays and either nosupplement or a protein supplement with 0, 2.5,5, or 7.5 g/kg BW of corn (Sanson et al.,unpublished data). Hay DM and NDF intakedecreased quadratically with increasing level ofcorn supplementation. Little effect was seen onforage DM1 until 7.5 g/kg BW of corn wassupplied, at which time both hay DM and NDFintake were decreased by 20 percent. Total dietDM1 increased with increasing level of cornsupplementation, until 7.5 g/kg BW of corn wasreached, when it was reduced by 7 percent.Digestible diet DM1 responded in a similarfashion. In contrast, total diet DM1 and totaldiet digestible DM1 by lambs consumingmedium- and high-quality forages were notaffected by level of supplemental corn, butforage DM1 decreased linearly with increasingcorn supplementation.

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Lake et al. (1974a; 1974b) reported that steersgrazing irrigated pasture and supplemented withcorn had higher gains than unsupplementedanimals. Heifers fed medium-quality (9 percentCP, 56 percent DMD) native meadow hay andsupplemented with 0.7 or 1.4 kg of corn orbarley gained more weight thanunsupplemented heifers (Sanson et al., 1993).As the level of supplement increased, heifergains increased linearly, with no differencebetween corn and barley fed in similar amounts.In contrast, cows consuming native meadowhay (7 percent CP, 51 percent IVDMD) andsupplemented with 0, 0.9, or 1.8 kg of corn hadsimilar performance, although there was a trendfor increase in gains as level of cornsupplementation increased (Sanson andClanton, 1989). These data indicate thatresponses in forage digestion and intake, andanimal gain to supplementation are different formedium-quality forages than low-qualityforages (Vanzant et al., 1990; Sanson andClanton, 1989).

Supplement Energy/Protein Interactions

Classification of supplements as either energyor protein is somewhat confusing, because bothtypes of feeds contain energy and protein. Infact, natural protein supplements usuallycontain similar energy levels as energysupplements. For example, nutrientcomposition tables (NRC, 1984) list the TDNcontent of soybean meal to be 84 to 87 percent,whereas barley and corn contain 84 and90 percent TDN, respectively. However, thecarbohydrate composition of protein and energysupplements may differ substantially. The totalcarbohydrate contents of barley and corn (82.3and 84.0 percent, respectively) areapproximately twice that of soybean meal (37.4to 41.3 percent), and the NSC contents are 64.3and 75.6 percent in barley and corn,respectively, compared to 29.8 to 32.2 percentfor soybean meal (Sniffen et al., 1992).

The levels of both energy and protein insupplements are important, and often theseinteract. With mature forages, there may not be

adequate nitrogen for microbial fermentation of.fiber, and additional protein from either a"protein" or an "energy" supplement may resultin improved forage utilization. Researchersoften try to remove the interaction of proteinand energy by attempting to keep the level ofone constant while varying the other. Theconcept is valid, but difficult to accomplishbecause of differences in protein degradabilityand carbohydrate content. Creatingisonitrogenous or isocaloric supplements doesnot mean that N or energy from differentsupplements will be available at the same rate.It becomes more complex when developingisocaloric supplements, because protein andenergy feeds both supply energy, yet the effectthat energy from amino acids has on microbialfermentation in the rumen may be different thanthe effect that NSC or structural carbohydrateshave on fermentation. When barley andsoybean meal are fed at the same level of DM,equal levels of energy would be provided;however, soybean meal provides much lessstarch than barley. Effects of supplementscontaining combinations of oil meals and cerealgrains on forage utilization have been variable(Williams Ct al., 1953; Fontenot et al., 1955;Elliott, 1967a, 196Th; Rittenhouse et al., 1970),and performance of animals supplemented withvarious levels of protein and energy has notbeen consistent (Norman, 1963; Bellows andThomas, 1976; Davis et al., 1977; Hennessy etal. 1981; Sanson et al., 1990). The variableresults may be due in part to different levels ofNSC in supplements that are formulated to beisocaloric.

Another approach that has been used is to feedthe supplement in increasing amounts. Withthis approach, an attempt is made to control thelevel of either protein or energy and allow theother to increase. However, this results indifferent amounts of DM being fed, which alsomay affect the utilization of the basal forage.Because of the interaction between protein andenergy in supplements, and its effect on forageutilization, it is important to understand theimpact that the design of the supplementaltreatments can have on the outcome of theexperiment.

29

Pruitt et al. (1993) supplemented cows grazingnative winter range with two levels of proteinand energy. Cows received 0.32 kg CP and3.92 Mcal ME, 0.32 kg CP and 10.64 Mcal ME,0.64 kg CP and 7.78 Mcal ME, or 0.64 kg CPand 10.91 Mcal ME. Increasing supplementalenergy at the low level of CP did not increasecow weight gains. However, increasingsupplemental energy at the higher level of CPincreased weight gain by 9.5 kg.

Cattle grazing dormant native winter rangewere fed supplements containing 0.13 kg CPand 1.18 kg TDN, 0.28 kg CP and 1.18 kgTDN, or 0.28 kg CP and 0.72 kg TDN duringthe last third of gestation (Sanson et al., 1990).Cows receiving 0.28 kg CP and 0.72 kg TDNgained 4 kg during this period, cows receiving0.28 kg CP and 1.18 kg TDN lost 18kg, andcows receiving 0.13 kg CP and 1.18 kg TDNlost 55 kg. An interaction betweensupplemental protein and energy was seen inthis study, with cows receiving low CP andhigh TDN losing the most weight, cowsreceiving high CP and low TDN gainingweight, and cows receiving high CP and highTDN losing an intermediate amount of weight.Differences in the degradability of the proteinsources may explain some of the interactions.

Summary

Despite the negative effects on forage digestionand intake that can result, energysupplementation of forage diets can increaseanimal performance due to an increase indigestible OM intake, a shift in rumenfermentation pattern to a greater proportion ofpropionate, and an increase in the flow ofundigested feed and microbial protein to theintestine (Galyean and Goetsch, 1993).

Data in this paper indicate that the effect anenergy supplement has on the utilization offorage is dependent on the composition of thesupplement, the level at which it is fed, and thequality of the forage. Supplements high in NSCmay have a negative effect on utilization ofmature, low-quality forage; the amount of

negative effect depends on forage quality,amount of supplement fed, and the grazingconditions. In contrast, supplements low inNSC have a positive associative effect on low-quality forages and may increase forage intakeand digestibility, along with the energy value ofthe forage. Associative effects of energysupplements (both high and low NSC) onmedium- and high-quality forages appear to bemore negative compared with their effects onlow-quality forages, and often result in adepression of forage intake.

This paper does not suggest that feed grains orother high-NSC supplements should never befed with low-quality forages. In situationswhere forage is in short supply, it may be moreeconomical to discount the energy value of theforage and to use grain to provide the additionalrequired energy. Using traditional methods tocalculate energy intake, and not correcting forassociative effects between forages andsupplements by adjusting energy value andintake of the forage, may result in over- orunder-estimation of energy intake.

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Villalobos, G., D.C. Adams, T.J. Klopfenstein,and LB. Lamb. 1992. Evaluation ofhigh quality hay as a winter supplementfor gestating beef cows in the sandhillsof Nebraska. Proc. West. Sec. Am. Soc.Anim. Sci. 43:367.

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.0

o7

O25 '-

0.00

-os0

Loo

38

Furgs CP:*

Figure 1. Predicted change in DM1 with increasing forage CP and levels of supplemental starch rangingfrom 0.1 to 0.5% BW.

FUrB9e CP,

Figure 2. Relationship between substitution rate and forage CP. Data based on 116observations in literature (R2 = 0.51, P < 0.01).

10 14

IA P4 O Th 4? 4R 4

Tim. øf ncubti*fl

Figure 3. Influence of increasing amounts of supplement non-structuralcarbohydrates (NSC) and time of incubation oncarboxymethylcellulose activity (Surber, et al., 1996).

39

Introduction.

What Supplement is Best?

To this juncture, this publication has addressedthe concept of supplementation, protein and(or) energy considerations, and mineral andvitamin supplementation of low-qualityroughages. This chapter will focus on proteinsupplementation building on previous chaptersand wilibegin to address the simple question of"what supplement is best?" Unfortunately, likemost simple questions, the answers are notstraightforward. In fact, evaluating varioussupplements is an ongoing process for ranchersand university faculty who focus onsupplementation strategies. There arenumerous types or "physical forms" ofsupplemental protein available. In addition, theBeef NRC (1996) has promoted a more detailedevaluation of protein requirements and feedcharacteristics to achieve optimal production.This improvement in protein characterizationhas, in turn, inadvertently promoted increasedinterest in finding the ideal supplement. Theinfluence of supplemental degradable (DIP)versus undegradable intake protein (UTP) onutilization of low-quality roughages is currentlybeing evaluated. What fits a given productionscenario will depend on a number of factors,including cost of the protein, ease andpracticality of feeding the supplement, as wellas productive stage and nutritional status of theanimal.

PHYSICAL FORM OF CRUDE PROTEIN FORSUPPLEMENTATION OF LOW-QUALITY ROUGHAGES.

Tim DelCurtoEastern Oregon Agricultural Research Center, Union Station

Oregon State University, Union, OR 97883

Ken OlsonDepartment of Animal, Dairy, and Veterinary Sciences

Utah State University, Logan, UT 84322-48 15.

40

Physical Form of Supplemental Protein.

There is limited information availableconcerning the efficacy of various types offeeds that might be used as sources ofsupplemental protein. The most commonsupplemental protein feed sources are derivedfrom oilseed byproducts such as soybean mealand cottonseed meal (Table 1). These sourcesof supplemental protein offer severaladvantages, including high concentrations ofcrude protein (i.e., soybean and cottonseedmeal consistently have at least 50 and45 percent CP, respectively) and energydensities similar to cereal grains. Thus, weusually consider these supplements as proteinsources, they also provide significant energycontributions. However, these feed sources aresometimes expensive. As a result, identifringless expensive alternative feed sources thatprovide supplemental protein would bebeneficial to ruminant livestock producers.

Other potential oilseed supplements includecanola meal, sunflower meal, rapeseed meal,and crambe meal. However, little research hasbeen conducted to evaluate their value assupplements to low quality forages for beefcattle. Seoane et al. (1992) supplemented steersreceiving a medium-quality grass hay(15.8 percent CP) with canola meal and foundthat ADG was improved by 60 percent and hayintake was improved by 8 percent. Total dietdry matter digestibility was unaffected, butfiber digestion was decreased by canola meal.Coombe et al. (1987) evaluated rapeseed orsunflower meals as supplements for growingsheep grazing low-quality grass pastures. Sheep

receiving no supplement or a urea supplementlost weight, whereas sheep receiving sunflowermeal gained weight. Intake of rapeseed mealwas low and variable, and resultant sheepperformance was also variable and intermediateto performance of control and sunflower-mealsupplemented sheep. Crambe seed is anotheroilseed that provides a high-protein meal afteroil extraction. Caton et al. (1994) comparedcrambe meal to soybean meal, and found thatOM and fiber digestion were similar, but Ndigestion was greater for crambe mealindicating that it may have higher DIP thansoybean meal.

Other potential supplements include wholesoybeans (Albro et al., 1993), and wheatmiddlings (Ovenell et al., 1991; Sunvold et al.,1991). In a study evaluating whole soybeans,extruded soybeans and soybean mealsupplements with low-quality meadow hay(6.5 percent CP), feed efficiency and gain ofgrowing steers were similar (Aibro et al.,1993). Likewise, wheat middlings have beenshown to improve low-quality-forageutilization but not to the same extent asisonitrogenous mixtures of soybean meal andsorghum grain (Sunvold et al., 1991), orsoybean meal and corn grain (Ovenell et al.,1991).

In the Pacific Northwest and IntermountainWest, alfalfa hay or cubes are often thesupplement of choice because of competitivepricing and easy accessibility to thesupplements. Studies comparing alfalfa andalfalfa products to oilseed-based supplementshave yielded variable results. Work fromeastern Montana (Cochran et al., 1986) andNew Mexico (Judkins et al., 1987) haveindicated that alfalfa pellets or cubes are aseffective as cottonseed cake when fed on anequal protein basis (Table 3). DelCurto andcoworkers (1990c) found that sun-cured alfalfapellets promoted higher forage intake andbetter maintenance of mature cow weight andbody condition compared to long-stem alfalfahay or soybean meal/sorghum grainsupplements. Increasing levels of supplementalalfalfa often cause a quadratic effect on intake

41

of low-quality forages (DelCurto et al., 1991;Vanzant and Cochran, 1994). Thus, totalrations should be balanced, but exceeding theCP requirements with increased supplementalalfalfa will result in substitution for potentialintake of low-quality forage. In general, theseresults suggest that alfalfa provides the samebenefits as other protein supplements when fedon an equal crude protein basis (Table 1).Alfalfa hay may have an added advantagebecause it is easily transported and handled byranchers, whereas oilseed supplements mayrequire additional equipment such as feedbunks and storage bins. Furthermore, alfalfahay has been shown to be comparable to alfalfapellets whether fed daily or on an alternate daybasis (Brandyberry et al., 1994).

While alfalfa is a very versatile proteinsupplement with easy application to many beefproduction scenarios, producers should becareful to make sure the energy requirementsare met and body condition reserves areadequate during winter feeding periods.Alfalfa can effectively meet CP requirements inrations with low-quality roughages; however,alfalfa does not have the caloric density of theoilseed meals or other byproduct feeds (Table1). In fact, alfalfa is similar to moderate tohigh quality grass hay in terms of energydensity. Thus, if cows are energy deficient andmarginal in body condition (fat reserves),supplements with higher energy density may bemore appropriate.

Another potential supplement for low-qualityforages is high-quality grass hay. Horney et al(1996) suggested that high-quality fescue hay(11.9 percent CP) supplementation of grassstraw (4.1 percent CP) yielded beef cattleperformance that was similar to or better thanthat of cows receiving alfalfa hay supplements(19 percent CP). Likewise, Villalobos et al.(1997) evaluated cow performance and steerdigestion responses to supplementation with a15 percent CP grass compared to a soybeanmeal and wheat grain mixture while consumingdormant Nebraska Sandhills range forage. Bothsupplements improved cow performance by asimilar amount over control cattle not receiving

supplements. Forage intake was unaffected, butboth supplements slightly depressed foragedigestibility. These studies suggest that higherquality grass hays are adequate supplements forlow-quality roughages.

Use of feeds with high UIP or "bypass" proteinis generally not a preferred strategy tosupplement low-quality roughages. Theoptimal time to use low-quality roughages isduring the last half ofpregnancy. During thistime (after weaning), cows are most suited toutilize cheap, low-quality roughage resourcesbecause they are not lactating and thus, are atthe lowest nutrient requirements of their annualproduction cycle. Also during this time, aminoacid requirements of the cow are adequatelymet by microbial cell protein reaching thelower gut. Thus, feeds with high levels of UIPsuch as feather meal, corn gluten meal, bloodmeal, and other "bypass" supplements can beused (Alawa et al., 1986; Fleck et al., 1988),but they do not offer an advantage over lessexpensive feeds with high levels of DIP (Table1). In fact, the Beef NRC (1996) equationsgenerally underscore that DIP is the criticalprotein fraction to supplement with low-qualityroughages. The relative successes of thenumerous supplements described aboveillustrate the need to provide supplementalprotein to beef cattle consuming low-quality,nitrogen-deficient diets. However, the generalsuccess of all supplements suggests that site ofprotein degradation (ruminal versus intestinal)is not a major consideration with the mature,non-lactating beef cow.

Optimal Protein Concentration

Numerous researchers have evaluated differingprotein concentrations as well as protein toenergy ratios with variable results in terms ofproviding consistent recommendations.DelCurto et al. (1990a,b) suggested that a26 percent CP soybean meal-sorghum grainsupplement was an optimal concentration forlow-quality tallgrass prairie forage whencompared with 13 and 39 percent CPsupplements. In these studies, all supplements

42

provided the same amount of energy, but weresomewhat confounded by source of energywith high starch content in the low proteinsupplements. Likewise, in a study evaluatingwheat middlings in 15, 20, and 25 percent CPsupplements, Sunvold et al. (1991) suggestedthat 20 percent was best for enhancement offorage intake whereas reduced benefits werereported at the 25 percent CP level. Bothresearchers indicated negative effects of lowprotein concentrations, including reducedintake and digestibility, which was presumablydue to the high starch content of the low proteinsupplements.

Optimal protein concentration of foragesupplements is less easily defined. Homey etal. (1996) found that high-quality meadow hay(11.9 percent CP) was comparable to alfalfahay (19.0 percent CP) when used as asupplement to tall fescue straw (4.1 percentCP). In fact, cows supplemented with meadowhay gained more weight and tended to lose lessbody condition than alfalfa hay-supplementedcows; presumably due to the greater quantity ofmeadow hay fed to provide similar proteinlevels. Likewise, Weder et al. (1998)conducted a series of experiments evaluatingthe influence of alfalfa hay quality on intake,forage use, and subsequent performance bybeef cattle consuming low-quality roughages.Alfalfa hays ranging in quality from 15 to21 percent CP did not influence intake anddigestibility of the low-quality basal diets nordramatically alter beef cattle weight and bodycondition status when fed to provide equalamounts of protein. Therefore, in an alfalfahay market that places a premium on CPconcentration, beef cattle producers shouldlook at feeder quality alfalfa as a viablesupplement to low-quality roughages.

Use of NPN Supplements

Nonprotein nitrogen (NPN) supplements arecommonly used in both hand-fed and self-fedsupplements. Compared to natural proteinsupplements, NPN sources are usuallysubstantially cheaper. Therefore, the use of

NPN ingredients yields a substantial economicadvantage. However, NPN has not been aseffective as natural protein sources whensupplemented to cattle consuming low-qualityroughages. Summarizing six experimentsevaluating the efficacy of urea and feed-gradebiuret in supplements fed to cattle on winterrange, Clanton (1978) reported decreasedperformance with supplements containinggreater than 3 percent urea or 6 percent biuretas compared to cattle receiving all naturalprotein supplements. Likewise, Rush andTotusek (1976) found that cows maintained onwinter range forage lost less weight when anatural protein supplement was fed comparedto isonitrogenous supplements containing ureaand biuret. Numerous other researchers havealso observed depressions in expected beef cowperformance when NPN is substituted for aportion of a natural protein in a supplement(Raleigh and Turner, 1968; Williams et al.,1969; Oltjen et al., 1974). Köster et al. (1997)substituted graded levels of urea for sodiumcaseinate so all supplement treatments werebased entirely on DIP and were isonitrogenous,but differed in ratio of NPN to true protein.Intake of dormant tallgrass prairie forage(2.4 percent CP) was unaffected by treatment,but ruminal and total tract digestibility of OMand NDF, as well as digestible OM intake, alldeclined quadratically, with the rate of declineincreasing as urea content increased. It shouldbe noted that in all the above performancestudies, special attention was devoted toassuring proper sulfur to nitrogen ratios in theNPN supplements. Likewise, while the NPNsupplements did not yield equal responses tonatural protein supplements, positive responsesto the improved N status were observed.

Many potential explanations exist regardingwhy NPN is limited in potcntial as a source ofN for ruminants consuming low-qualityroughages. One of the major problemsassociated with efficient utilization of urea, themost common NPN source, is the rapid releaseof ammonia. Bloomfield et al. (1960) indicatedthat urea hydrolysis occurred four times fasterthan uptake of the liberated ammonia, which inturn, increases the passive transport gradient

43

and pH, thus making conditions optimal forabsorption of ammonia into the blood(Bloomfield et al., 1963). As a result, much ofthe ammonia released from urea is absorbedbefore the ruminal bacteria can efficientlyutilize it. Additionally, Chalupa (1968)suggested that assimilation of ammonia byruminal bacteria might also be limited byavailability of carbon skeletons, such asbranch-chain VFA, and other nutrients. Sulfuris a common nutrient suggested to impact theutilization of ruminal nitrogen due to theirinterrelated role in microbial cell proteinsynthesis. The advantage of natural proteinsources, in this scenario, is that degradableproteins that are broken down and deaminatedprovide carbon skeletons and other essentialnutrients for microbial cell protein assimilation.These results indicate that NPN might be amore viable supplement if the availability ofammonia was more closely synchronized withfermentative processes and essential nutrientsfor bacterial growth.

Summary and Implications

Numerous supplements are available that willprovide protein to beef cattle consuming low-quality roughages. The "ideal supplement" isone that best fits the target animals nutritionalneeds, is easiest to handle and present to thetarget animals, and is most economical topurchase and feed. Obviously, manysupplements may be appropriate in specificsituations. While oilseed supplements are themost common supplements utilized with low-quality forages, numerous other supplementssuch as alfalfa, wheat middlings and high-quality meadow hays can be used effectively.Protein supplementation is critical to theoptimal use of low-quality roughages , yetenergy content or density may be importantdepending on body condition status andsubsequent reproductive success of the cowherd.

In general, natural protein appears to be themost beneficial supplement for high-fiber, low-quality roughages in ruminant diets.

Nonprotein nitrogen does not appear to be asbeneficial as natural protein supplementation.However, the differences in response can beminimized and NPN can offer economicadvantages over natural protein. Futhermore,feeding of slowly degraded or bypass protein,

Table 1. Chemical composition of feed ingredients with potential for use assupplemental protein for low-quality forages.'

as well as potentially "rate limiting" aminoacids appear to show inconsistent responsesand do not appear to show any substantialimprovements over traditional supplementalprotein sources used with mature, nonlactatingbeef cows consuming low-quality roughages.

1

Adapted for the National Research Council Nutrient Requirements of Beef Cattle (1996).

44

Protein source CP, % DIP, % UIP, % TDN, %ME,Meal/kg

Brewers grain 26.0 40.9 59.1 70.0 2.53Canola meal 40.9 67.9 32.1 69.0 2.49Coconut meal 21.5 61.6 38.4 64.0 2.31Corn gluten meal 46.8 38.1 61.9 84.0 3.04Cottonseed meal, mech 44.0 57.0 43.0 78.0 2.82Cottonseed meal, sol-41 % CP 46.1 57.0 43.0 75.0 2.71Cottonseed meal, sol-43 % CP 48.9 57.0 43.0 75.0 2.71Distillers grain 29.7 45.1 54.9 90.0 3.25Soybean meal-44 52.9 80.0 20.0 84.0 3.04Soybean meal-49 49.9 65.0 35.0 87.0 3.15Soybean whole 40.3 65.0 35.0 94.0 3.40Sunflower meal 25.9 38.3 61.7 65.0 2.35Urea 291.0 100.0 0.0 0.0 0.00Alfalfa hay, vegetative 21.7 86.0 14.0 64.0 2.31Alfalfa hay, early bloom 19.9 84.0 16.0 62.0 2.24Alfalfa hay, mid bloom 17.0 82.0 18.0 60.0 2.17Alfalfa hay, full bloom 13.0 77.0 23.0 56.0 2.02Wheat middlings 18.4 77.2 22.8 83.0 3.00Tall fescue hay 9.1 67.0 33.0 56.0 2.02Meadow hay 13.4 77.0 23.0 60.0 2.17

Table 2. A Summary Of Investigations Comparing Supplementation Strategies With Low Quality Roughages. Effect On Beef Cattle Weight Change, Body Condition Change And Reproductive Efficiency.

Sunirnary is not all inclusive, but lists studies with differing forage bases, treatment structures and productive classes of livestock.bDefmitiOn of abbreviations BW = body weight, BC = body condition (1-9 scale), CP = crude Protein, ADG = average daily gains

SupplementaryinformationQuantities of supplementprovided were adjusted to insureequal portions of CP

Supplements were isocaloricmixtures of soybean meal andsorghum grains. Tendency forincreased birth weights and calfADG with dams who receivedhigh concentrations ofsupplemental protein

Quantity of supplementsprovided were adjusted to insureisonitrogenous treatments. Noreproductive differences wereobserved.

Quantity of supplementsprovided were adjusted to insureisonitrogenous treatments.

Heifers receiving cottonseedcake were heavier at breedingand had greater conception rates.

Calf ADG and birth weight tendto increase with increasing levelsof supplementation. Calvinginterval declined with increasinglevel of dam's nutrition. Allcows were individually fedsupplements during 112 dfeeding period.

Calf ADG and birth weight wereincreased with 3.0 and 4.5 kgsupple. Treatments. All cowswere individually fedsupplements during 70 d feedingperiod.

Reference Forage or substrateSupplementTreatments

Class of livestock BWChange, kg

BCChange

Cochranetal., 1986 Dormant mixed grass prairie 1) Control, no supple. 517 kg pregnant cows -0.11 -0.5forage 3.0-6.5 % CP Feeding 2) Alfalfa cubes, 16.5 % CP (151 hd) 24 0.5period: 3) Cottonseed meal/barley cake, 21.6 14 0

-84 d, year 1-98 d, year 2

DelCurto et al., Dormant tallprairie forage 1) 13%CPsupple.fed@0.5%BW 454 kg pregnant cows -11 -0.71990b Feeding period: 2) 26% CP supple. fed @0.5 % BW (99 hd) 12 -0.4

-Mid November to early 3) 39% CP supple. fed @0.5% BW 17 -0.2February (84 d)

DelCurto Ct al.,l990c

Dormant tallprairie forageFeeding period:

4) 25 % CP SBMlsorghum supple. @0.48 % BW5) 17%CPalfalfahayfed@0.7%BW

488 kg pregnant cows(84 hd)

-32

-0.4-0.5

-Mid November to early 6)17 % CP dehydrated alfalfa pellets fed @0.7 % BW 19 -0.3February (84 d)

Judkins et al.,1987

Dormant Blue Grama range-11.5 % CP feeding:

1) Control, no supple.2) Cottonseed meal (47 %) fed alternate days @ 1.7 kg/hd

241 kg heifers -325

-Mid February to late April 3) Alfalfa hay (17.5 % CP) fed alternate days @ 3.6 kg/hd 24(104d)

Wallace, 1987 Dormant Blue Grama range 1) Cottonseed cake (41 % CP): 3.2 kg 2 x weekly 227 kg heifers 34-9.6 % CP. Feeding Period: 2) Corn grain cube (9.4 % CP): 2.91 kg 2 x weekly -2-Mid December to mid May 3) Corn grain cube (9.4 % CP): 83 kg daily 10

(150 d)

DelCurto et al., Dormant sagebrush-steppe 1) Control, no supple. 463 kg pregnant cows -30 -1.21991 rangelands: 2) 1.5 kg alfalfa/hd/d (5.3 BC) 9 -1.2

-Year 1 3) 3.0 kg alfalfa/hdld 30 -0.1

-6.8 to 5.4% CP 4) 4.5 kg alfalfa/hd/d 44 0.248hd- 112 d feeding period

-Year 2 1) Control, no supple. 471 kg pregnant cows -62 -2.1.-4.2 to 4.8 % CP 2)1.5 kg alfalfa/hd/d (5.3 BC -15 -0.8-72 hd 3) 3.0 kg alfalfa/hd/d 5 -0.2-70 d feeding period. 4) 4.5 kg alfalfa/hdld 11 0.2

Table 3. A Summary Of Investigations Comparing Supplementation Strategies With Low Quality Roughages: Effect On Intake And Digestion

(0.37 % BW)

Supplements wereisonitrogenous withincreasing level of corn as CFconcentration decreased.

Supplements were isocaloricmixtures of 40 % wheatmiddlings and mixtures ofsoybean meal and sorghumgrain.2x2 factorial contrasting highandlowlevelsofcrudeprotein (treatments 1 & 2 vs 3&4(withhighandlowlevelsof supplemental energy(treatments 1 &3vs2&4).

Earlyratesofinvitrodigestion were improved withsupplementation. Digestakinetics was increased withsupplementation.

Reference Forage or substrateSupplementTreatments

Class of livestock

Dry matterintake. % BW

Total

Forage digestion

Forage DM NDF

A. Protein levels and protein/energy ratios:Church and Santos,1981

3.8 % CF wheat straw 1) 0 g/kg BW.75 protein2) 1 gikg BW.75 protein

270 kg heifers 1.321.56

1.321.64

47.155.8

-

-

3) 2 g/kg BW.75 protein 1.72 1.84 49.0 -

4) 3 g/kg BW.75 protein 1.79 1.94 48.6 -

5) 4 g/kg BW.75 protein 1.74 1.91 51.9 -

DelCurto et al.,1990a

Dormant tallgrass prairie hay(2.9 % CR)

1) Control, no supple.2) 13 % CF supple.

242 kg steers 0.870.85

0.871.27

35.544.8

37.929.9

3) 26%CF supple. 1.36 1.76 48.4 39.94) 39%CP supple. 1.21 1.62 48.8 38.6

Sanson et al.,1990

Sanhills meadow hay(4.3 % CP)

I) Control, no supple.2) 48.5 % CF supple.

550 kg steers 1.82.1

1.82.3

49.556.7

50.052.7

3) 24.5% CF supple. 2.0 2.4 59.2 51.14) l6.0%CPsupple. 1.6 2.2 60.0 49.5

Sunvold et al.,1991

Dormant tallgrass prairie hay(2.0%CP)

1) Control, no supple.2)15 % CF supple.

422 kg steers 1.031.12

1.031.49

34.749.3

46.251.2

3) 20 % CF supple. 1.62 1.99 48.8 53.24) 25 % CF supple. 1.70 1.07 49.8 55.5

DelCurto et aL,1990a

Dormant tallgrass prairie hay(2.6 % CP)

1) 22% CF supple. fed @0.3% BW2) 11%CP supple. fed@0.6%BW

332 kg steers 1.210.82

1.511.42

39.146.1

49.244.3

3) 44 % CF supple. fed @ 0.3 % BW 1.07 1.37 45.9 50.94) 22 % CF supple. fed @ 0.6% BW 1.51 1.75 47.5 48.0

1) 22 % CF supple. fed @0.3% BW 401 kgsteers 1.30 1.60 -2)11 %CFsupple.fed@0.6%BW 1.17 1.773) 44% CF supple. fed @0.3 % BW 1.71 2.014) 22 % CF supple. fed @ 0.6 % BW 1.49 1.09 -

McCollom and 6.1 % CF prairie hay 1) Control, no supple. 2l4kgsteers 1.69 1.69 49.9Galyean, 1985 2) Cottonseed meal, 0.8 kg/d 2.15 2.52 53.5

Supplementaryinformation

Increasing levels of proteinwere achieved bysupplementing increasingquantities of soybean meal.

Isocaloric supplement fed at.4%BW

Table 3. A Summary Of Investigations Comparing Supplementation Strategies With Low Quality Roughages: Effect On Intake And Digestion.' (Continued)

Sunmiary is not all inclusive, but lists studies with differeing forage bases, treatment structures and productive classes of livestock.b Defmition of abbreviations: BW = body weight, CF = crude protein, DM dry matter, NDF neutral detergent fiber.

Quantities of supplementedfeed were adjusted to beisonitrogeous.

Treatments 2 & 3 provideequal energy levels.

Initialrateofdigestionwasimproved but evened out inlater in situ periods

Quantities of supplementedfeed were adjusted to beisonitrogeous

Differences between years Iand 2 were attributed toseverity of weather andlimited availability of foragein year 2.

Reference Forage or substrateSupplementTreatments Class of livestock

Dry matterintake. % BW

Total

Forage digestion

Forage DM NDF

B. Physical Form of Supplemental ProteinDelCurto et al.,1990c

Dormant tallgrass prairie hay(2.6 % C?)

1) Control, no supple.2) Soybean meal/sorghum grain fed at

259 kg steers 0.491.07

0.491.55

42.746.3

57.348.5

0.48 % BW. 1.05 1.75 49.6 52.63)17% CP alfalfa hay fed at 0.7% BW 1.21 1.88 44.2 4584)17.4 % CP dehydrated alfalfa pellets

fed at 0.68 % BW

Judkins et al.,1987

Blue grama range (11.5%) 1) Control, no supple.2) 23 % CP alfalfa pellets

230 kg steers 1.080.77

1.081.41

3) 47.7 % CP cottonseed cake 0.96 1.29

Sunvold et al.,1991

Dormant tallgrass prairie hay(2.4 % CP)

1) Control, no supple.2) Soybean meal/sorghum grain fed at

374 kg steers 0.871.07

0.871.39

43.949.4

54.351.2

0.32% BW 0.99 1.38 50.6 54.13) Wheat middlings fed at 0.39% BW 1.15 1.92 50.4 49.84) Wheat middlings fed at 0.77 % BW.

C. Supplementation Under Grazing Conditions:

Catonetal., Blue grama rangelands 8.1 % 1) Control, no supple. Hereford x Angus 0.93 0.93 46.7 3.01988 CP (OM basis) 2) Cottonseed meal, 0.83 kg/d 454 kg steers 1.16 1.34 49.6 %/h

(0.18 %BW) 3.4%/h

Judkins et al.,1987

Blue grama range (11.5%) 1) Control, no supple.2) 23 % CF alfalfa pellets

230 kg steers 1.080.77

1.081.41

-

3) 47.7 % CF cottonseed cake 0.96 1.29 -(Forage)

Kartchner, 1981 Winter range forage: 1) Control, no supple. 458 kg dry pregnant 1.89 1.89 54.9 54.9Blue grama range 6.0 % CP - 2) 1.5 kg cottonseed meal fed on Herford cows 1.78 1.94 53.2 52.9Year 1 alternate days 1.71 1.86 54.2 51.7

3)1.4kg barley fed alternate daysBlue gama range 1) Control, no supple. 497 kg dry pregnant 1.37 1.37 40.6 40.68.1 %CP-Year2 2)1.5, 1.5 and 2 kg SBM fed Monday,

Wednesday and Friday, respectivelyHerford cows 1.61

1.271.751.40

46.438.8

48.634.3

3)1.3, l.3and2kgbarley

Supplementaryinformation

Supplemental treatmentsprovided equal quantities ofME and crude protein.

Literature Cited

Alawa, J.P., G. Fishwick, J.J. Parkins, R.G.Hemingway, and T.C. Aitchison. 1986.Influence of energy source and dietaryprotein degradability on the voluntaryintake and digestibility of barley strawby pregnant beef cows. Anim. Prod.43 :201-209.

Aibro, J.D., D.W. Weber and T. DelCurto.1993. Comparison of whole rawsoybeans, extruded soybeans or soybeanmeal/barley on digestive characteristicsand performance of weaned beef steersconsuming mature grass hay. J. Anim.Sci. 71:26.

Bloomfield, R.A., G.G. Gamer, and M.E.Muhrer. 1960. Kinetics of ureametabolism in sheep. J. Anim Sci.19: 1,248.

Bloomfield, R.A., E.O. Kearley, D.O. Creach,and M.E. Mubrer. 1963. Ruminal pHand absorption of ammonia and VFA.J. Anim. Aci. 23:833.

Brandyberry, S.D., T. DelCurto and R.A.Angell. 1994. Physical form andfrequency of alfalfa supplementation forbeef cattle winter grazing northernGreat Basin rangelands. Oregon Agric.Exp. Sta. Special Rep. 935.

Caton, J.S., V.1. Burke, V.L. Anderson, L.A.Burgwald, P.L. Norton, and K.C. Olson.1994 Influence of crambe meal as aprotein source on intake, site ofdigestion, ruminal fermentation, andmicrobial efficiency in beef steers fedgrass hay. J. Anim. Sci. 72:3,238-3,245.

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Caton, J.S., A.S. Freeman and M.L. Galyean.1988. Influence of proteinsupplementation on forage intake, insitu forage disappearance, ruminalfermentation and digesta passage ratesin steers grazing dormant blue gramarangeland. J. Anim. Sci. 66:2,262-2,271.

CHALUPA, W. 1968. Problems in feedingurea to ruminants. J. Anim. Sci.27:207.

Chase, C.C. and C.A. Hibberd. 1987.Utilization of low-quality native grasshay by beef cows fed increasingquantities of corn grain. J. Anim. Sci.65:557.

Church, D.C. and A. Santos. 1981. Effect ofgraded levels of soybean meal and of anonprotein nitrogen-molassessupplement on consumption anddigestibility of wheat straw. J. Anim.Sci. 53:1,609.

Clanton, D.C. 1978. Non-protein nitrogen inrange supplements. J. Anim. Sci.47:765.

Clanton, D.C. 1982. Crude protein in rangesupplements. In: F. N. Owens (Ed.)Protein Requirements for Cattle.Symposium. pp. 228-234. OklahomaState Univ. MP-109, Stillwater.

Clanton, D.C. and D.R. Zimmerman. 1970.Symposium on pasture methods formaximum production in beef cattle:Protein and energy requirements forfemale beef cattle. J. Anim. Sci.30:122.

Cochran, R.D., D.C. Adams, P.O. Currie, andB.W. Knapp. 1986. Cubed alfalfa hayor cottonseed meal-barley assupplements for beef caows grazingfall-qinter range. J. Range Manage.39:361.

Coombe, J.B., A. Axelsen, and H. Dove. 1987.Rape and sunflower seed meals assupplements for sheep grazing cerealstubbles. Aust. J. Exp. Agric. 27:5 13-523.

DelCurto, T., R.A. Angell, R.K. Barton, J.A.Rose andS.C.Bennett. 1991. Alfalfasupplementation of beef cattle grazingwinter sagebrush-steppe range forage.Oregon Agric. Exp. Sta. Special Rep.880.

DelCurto, T., R.C. Cochran, D.L. Harmon,A.A. Beharka, K.A. Jacques, 0. Towneand E.S. Vanzant. 1990b.Supplementation of dormant, taligrass-prairie forage: I. Influence of varyingsupplemental protein and (or) energylevels on forage utilizationcharacteristics of beef steers inconfinement. J. Anim. Sci. 68:5 15.

DelCurto, T., R.C. Cochran, L.R. Corah, A.A.Beharka, E.S. Vanzant and D.E.Vanzant. 1990a. Supplementation ofdormant, taligrass-prairie forage. II.Performance and forage utilizationcharacteristics in grazing beef cattlereceiving supplements of differentprotein concentrations. J. Anim. Sci.68:532.

DelCurto, T., R.C. Cochran, T.G. Nagaraja,L.R. Corah, A.A. Beharka and E.S.Vanzant. 1 990c. Comparison ofsoybean meal/sorghum grain, alfalfahay and dehydrated alfalfa pellets assupplemental protein sources for beefcattle consuming dormant, tallgrassprairie forage. J. Anim. Sci. 68:2,901.

Fleck, A.T., K.S. Lusby, F.N. Owens, and F.T.McCollum. 1988. Effects of corn glutenfeed on forage intake, digestibility andruminal parameters of cattle fed nativegrass hay. J. Anim. Sci. 66:750-757.

49

Homey, M.R., T. DelCurto, M.M. Stamm, R.K.Barton and S.D. Brandybeny. 1996.Early-vegetative meadow hay versusalfalfa hay as a supplement for cattleconsuming low-quality roughages. J.Anim. Sci. 74:1,959.

Judkins, M.B., J.D. Wallace, M.L. Galyean,L.J. Krysl, and E.E. Parker. 1987.Passage rates, rumen fermentation, andweight change in protein supplementedgrazing cattle. J. Range Manage.40: 100.

Köster, H.H., R.C. Cochran, E.C. Titgemeyer,B. S. Vanzant, T. G. Nagaraja, K. K.Kreikemeier, and G. St. Jean. 1997.Effect of increasing proportion ofsupplemental nitrogen from urea onintake and utilization of low-quality,tallgrass-prairie forage by beef steers. J.Anim. Sci. 75:1,393-1,399.

McCollum, F.T. and M.L. Galyean. 1985.Influence of cottonseed mealsupplementation on voluntary intake,rumen fermentation and rate of passageof prairie hay in beef steers. J. Anim.Sci. 60:570-577.

NRC. 1996. Nutrient Requirements of BeefCattle. National Academy Press,Washington, DC.

Oltjen, R.R., W.C. Bums and C B Ammermen.1974. Biuret versus urea andcottonseed meal for wintering andfinishing steers. J. Anim. Sci. 38:975.

Ovenell, K. H., K. S. Lusby, G. W. Horn, andR. W. McNew. 1991. Effects oflactational status on forage intake,digestibility, and particulate passagerate of beef cows supplemented withsoybean meal, wheat middlings, andcorn and soybean meal. J. Anim. Sci.69:2,617-2,623.

Raleigh, R.J. and H.A. Turner. 1968. Biuretand urea in range cattle supplements.Proc. West. Sec. Amer. Soc. Anim. Sci.19:301.

Rush, I.G. and R. Totusek. 1976.Supplemental value of feed-grade biuretand urea molasses for cows on drywinter grass. J. Anim. Sci. 42:497.

Sanson, D.W., D.C. Clanton and I.G. Rush.1990. Intake and digestion of low-quality meadow hay by steers andperformance of cows on native rangewhen fed protein supplementscontaining various levels of corn. J.Anim. Sci. 68:595.

Seoane, J.R., A.M. Christen, D.M. Veira, and J.Fontecilla. 1992, Performance ofgrowing steers fed quackgrass haysupplemented with canola meal. Can. J.Anim. Sci. 72:329-336.

Sunvold, G.D., R.C. Cochran and E.S. Vanzant.1991. Evaluation of wheat middlings asa supplement for beef cattle consumingdormant bluestem-range forage. J.Anim. Sci. 69:3,044.

Vanzant, E.S., andR.C. Cochran. 1994.Performance and forage utilization bybeef cattle receiving increasing amountsof alfalfa hay as a supplement to low-quality, taligrass-prairie forage. J.Anim. Sci. 72:1,059.

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Villalobos, G., D.C. Adams, T.J. Klopfenstein,J.T. Nichols, and J.B. Lamb. 1997.Grass hay as a supplement for grazingcattle I. Animal performance. J. RangeManage. 50:351-356.

Wallace, J.D. 1987. Supplemental feedingoptions to improve livestock efficiencyon rangelands. In: R. S. White and R.E. Short (Eds.) Achieving Efficient Useof Rangeland Resources. Fort KeoghRes. Symp. Montana Agric. Exp. Sta.,Bozeman, pp. 92-100.

Weder, C.E., T. DelCurto, T. Svejcar, J.R.Jaeger, and R.K. Bailey. 1999. Theinfluence of supplemental alfalfaquality on the intake, use, andsubsequent performance of beefconsuming low-quality roughages. J.Anim. Sci. 77:1,266-1,276.

Williams, D.L., J.V. Whiteman and A.D.Tillman. 1969. Urea utilization inprotein supplements for cattleconsuming poor quality roughages onthe range. J. Anim. Sci. 28:807.

-4

Chapter 3. Mineral/Vitamin Supplementation

MACROMINERAL NUTRITION OF GRAZING RUMINANTS: LEVELS INFORAGES GROWN IN THE WESTERN U.S., AND EFFICACY OF

SUPPLEMENTATION

Elaine E. GringsUSDA-ARS

Fort Keogh LARRL, Miles City, MT 59301

Introduction

Maintenance of production suitable to today'sagricultural industry may requiresupplementation of mineral nutrients toruminant livestock. Under natural situations,animals make use of salt licks and, at times,bone chewing and other forms of pica tosupplement their diets with minerals. Inproduction situations, minerals may be suppliedto livestock in several forms, and knowledge ofmineral levels and bioavailability in feedstuffsare important to optimize mineralsupplementation economically with animalperformance.

In 1804, Theodore de Saussure made the firstanalysis of the ash of herbage. From hisexperiments, he concluded that plants do notabsorb minerals in the same proportion inwhich they occur in the soil; different soil typeshave a profound influence upon theconcentration of minerals in the same speciesof plants; the different plant parts differ in theirmineral concentration; and the percentage ofash reaches its maximum before flowering inherbaceous plants and then declines (Beeson,1941). More recent literature has dealt with thedifferent elements separately, but these fourconclusions generally hold true.

Changes in forage maturity affect both foragemineral level and bioavailability. For anelement to be biologically useful to an animal,it must first be absorbed, and then it must bepresent at its site of action when needed. Thelatter requirement might be affected by thechemical form in which the element is found inthe body, the ability of the body to store anelement and mobilize it when needed, and the

53

amount of excretion of the element from thebody. Both absorptive efficiency and theability of an animal to store and use an elementmay vary with the animal's age, nutritionalstate, and reproductive status. A large volumeof research has been devoted to determiningbiological availability of supplementaryminerals (see Ammerman et al., 1995, for areview), however, much less is known aboutthe availability of macrominerals from foragesand factors affecting that bioavailability.

Phosphorus

Phosphorus is commonly deficient for livestockon Western rangelands. Deficiencies inphosphorus result in depressed feed intake,growth, lowered reproductive performance, andmilk yield. The NRC (1996) lists thephosphorus maintenance requirement of cattleto be 16 mg P/kg body weight. Thisrequirement increases with pregnancy, growth,and lactation. Phosphorus is necessary forproper bone development, absorption ofcarbohydrates from the intestine, and forenergy transfer within cells. A very markedsecretion of phosphorus occurs through thesaliva in ruminants (Ben-Ghedalia et al.,1975), most of which is reabsorbed whilepassing through the intestine, so it is notentirely lost from the body. This can be ofsignificance in ruminants whose natural feedsare often deficient in phosphorus.

Phosphorus in forages. Phosphorus has animportant function in plants as an energycarrier and is found in sugar phosphates,coenzymes, nucleic acids, and phospholipids.Phosphorus decreases in concentration as plants

mature (McMillen et al., 1943; Rauzi et al.,1969). Declining phosphorus concentrationsare related primarily to decreases in the amountof live tissue as plants age. Phosphorus contentof dead tissue remains relatively constant andlow, whereas live tissue phosphorus is high inyoung tissue and decreases as the growingseason progresses (Greene et al., 1987; Gringset al., 1996). Live:dead ratios of availableforage may be a good indicator of phosphoruslevels in the diet. Livestock do select a diethigher in phosphorus than the average of whatis available, and this does need to be consideredin evaluating phosphorus needs. In addition tolowered concentrations in the forage,phosphorus absorption and retention have beenreported to decrease with increasing plantmaturity (Perdomo et al., 1977; Powell et al.,1978; Rosero et al., 1980; Vona et al., 1984).

Phosphorus supplementation. Phosphorus isstored in the bone, and this can be utilized inperiods of limited phosphorus intake. Theutilization of stored phosphorus can result invariations in response to supplementation.Factors influencing both dietary and storedphosphorus utilization include the calcium tophosphorus ratio, age of animal, sex, fat andenergy levels, environment, hormones, diseaseand parasites, protein and trace-element levels,chelating agents, and numerous others.

Range cows studied over a 5-year period inNew Mexico did not respond to phosphorussupplementation except in a drought year(Judkins et al., 1985). During the drought,phosphorus supplemented cows had a shorterpostpartum interval than did non-supplementedcows. Rib phosphorus levels declined duringlactation, but these levels recovered during thedry period, even when no phosphorus wassupplemented. Karn (1992) conducted a studyin North Dakota in which cows were given freeaccess to a phosphorus-containing salt mix.Cows consumed between 3 and 19 percent oftheir phosphorus requirement through thissupplementation method, and there were nodifferences in performance betweensupplemented and nonsupplemented cows. Thelack of response may have been related to the

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low phosphorus intake levels of thesupplemented cows. In a later study, Karn(1995) evaluated phosphorus supplementationfor heifers. There was no response in liveweight gain during the first year, whenHereford and Hereford x Angus cross heiferswere used; but in the second year, weight gainwas increased in Hereford x Simmental heifersfed phosphorus supplements compared tocontrols. Breed differences in mineralmetabolism have been observed for both cattleand sheep and may have affected response tophosphorus supplementation. These heiferswere used in subsequent studies, in whichphosphorus supplementation improved calfweaning weight in 3 out of 5 years, giving anaverage improvement in calf gain of 7.9 kgwith phosphorus supplementation (Kam, 1997).

Calcium

Calcium is the most abundant mineral in thebody and is required by animals for boneformation, proper neuromuscular irritability,and milk production. The calcium requirementfor maintenance of beef cattle is 15.4 mg/kgbody weight (NRC, 1996). Additional calciumis required for growth, pregnancy, and milkproduction. Calcium requirements listed byNRC do account for efficiency of calciumabsorption, which is considered to be 50percent of dietary intake.

Calcium in forages. Calcium is found in boththe vacuoles and cell walls of plants. In thevacuoles, it often precipitates as crystals of cal-cium oxalate. In the cell wall, calcium is foundin the middle lamella, where it forms insolublesalts with pectic acids.

Reports on calcium levels in relation to plantmaturity have been variable. In southernWyoming, calcium declined with maturity inblue grama but not in western wheatgrass(Rauzi et al., 1969). Halvorson and White(1981) found calcium tended to increaseslightly with age in vegetative and floral tillersof western wheatgrass and floral tillers of greenneedlegrass. Campbell (1973) reported that

calcium levels in plants grown on irrigatedpastures in northeastern Colorado did not varysignificantly from May to September. Thecalcium content of grass species grown insouthern Idaho was very erratic throughout theyear except for cheatgrass, which showed asteady decline (Murray et al., 1978). Thecalcium content of stems of timothy andbromegrass was observed to decrease withmaturity while the calcium levels in the leavesand heads of these species were observed toincrease (Pritchard et al., 1964). Calciumabsorption and retention has been reported todecrease with increasing plant maturity(Perdomo et al., 1977; Powell et al., 1978;Rosero et al., 1980; Vona et al., 1984). NeitherGreene et al. (1987) nor Grings et al. (1996)found calcium to vary consistently withlive:dead tissue class. Forbs were consistentlyhigher in calcium than grasses in both Texas(Greene et aL, 1987; Meyer and Brown, 1985)and Montana (Grings et al., 1996).

Calcium supplementation. Due to the variationof calcium in forages, levels of calcium in thediets of cattle grazing Western rangelands mayvary in an inconsistent pattern, falling bothabove and below animal requirements (Grings,1979). Cattle can compensate for short periodsof low calcium intake through use of bodystores. However, bone mobilization to obtaincalcium for physiological functions can havedetrimental effects on phosphorus status.

Calcium often is provided to grazing livestockas a by-product of meeting other nutrient needs.Legumes, fed as protein supplements, are highin calcium Phosphorus supplements often usemono- (16.4 percent calcium) or di-calcium(22 percent calcium) phosphate. The concernin supplying calcium is often the maintenanceof an appropriate ration of calcium tophosphorus to ensure adequate phosphorusabsorption.

Calcium:Phosphorus Ratio. Literatureconcerning the importance of a calcium tophosphorus (Ca:P) ratio is varied with regard toruminant nutrition. Simple-stomached animalshave an optimal Ca:P ratio of between 1:1 and

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2:1; but in ruminants, a ratio of 7:1 has beenfound to be satisfactory provided that thephosphorus in the diet is adequate and theimbalance is not long-term. Littlejohn andLewis (1960) reported that a Ca:P ratio of 7.5:1had no adverse effect on conception rate ofdairy heifers, but growth rate was decreased bythis high ratio. Ratios above 7:1 were reportedby Wise et al. (1963) to result in decreasedperformance and efficiency of food conversionto body weight gains in Hereford calves. Theseauthors also reported that a Ca:P ratio of 4.8:1was most favorable in terms of efficiency offeed conversion. Feeding a low phosphorusforage can result in negative calcium balances,even in animals fed "adequate" calcium levels(Grings and Males, 1987).

Potassium

In animals, potassium plays an important rolein the development of nerve impulses and inthe contraction of muscle. Potassiumrequirements for cattle are between 0.6 and0.7 percent of the diet.

Potassium in forages. Potassium does not forma stable structural part of any molecule withinplant cells, but it does act as a cofactor to manyenzymes. Grassland vegetation may bedeficient in potassium in winter months (Karnand Clanton, 1977). Thomas and Hipp (1968)observed that on sandy soils, heavy rains orrapid plant growth could deplete the availablepotassium in the soil in a matter of days.

The potassium content of the stems, leaves, andheads of several grasses decreases with in-creasing maturity (Pritchard et al., 1964; Rauziet al., 1969; Halvorson and White, 1981).Potassium concentrations of range grasses havebeen shown to be influenced greatly by live todead tissue ratios (Greene et al., 1987; Gringset al., 1996). Potassium in dead tissue wasalways low, whereas live tissue potassiumconcentrations were very high at the beginningof the growing period and declined over time.Decreases in potassium absorption andretention were found with increasing plant

maturity in cool-season forages (Powell et al.,1978). Potassium absorption decreased or didnot change, and potassium retention was notaffected by stage of plant maturity in freshtropical forages fed to sheep (Perdomo et al.,1977).

Potassium supplementation. Karn and Clanton(1977) reported that supplementation ofpotassium during the winter months preventeda depression in weight gains of weaned steercalves grazing sandhills range in Nebraska.Due to the high availability of potassium fromfeedstuffs, it can be supplemented easily whenneeded. Potassium concentrations insupplemental feeds such as hays and oilseedmeals are high and can make a significantcontribution to potassium intake if fed duringperiods when forage potassium is low.

Magnesium

Magnesium is necessary to activate manyenzyme systems as well as being necessary foroxidative phosphorylation. The magnesiumrequirement for lactating beef cows has beendetermined to be approximately 0.20 percent ofthe diet dry matter (NRC, 1996). For growinganimals, the requirement is 0.10 percent. Adeficiency of magnesium can lead to grasstetany, a deficiency disease that results inconsiderable death losses of animals grazing inthe world's temperate regions. Grass tetany ismore likely to affect older animals, because theability of the animal to mobilize bonemagnesium decreases markedly with age. Theavailability of magnesium to the animal is veryimportant to the incidence of tetany and maydepend upon the levels of potassium, nitrogen,and higher fatty acids in the diet (Jung 1977;Fontenot et al., 1960).

Magnesium in forages. Magnesium is anessential part of the chlorophyll molecule ofplants. It is also necessary to activate manyenzyme systems and is necessary for oxidativephosphorylation. It is found in highconcentrations in live tissue due to itsassociation with chlorophyll. Magnesium

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levels in the stems of several grasses werereported to decline with maturity, whereaslevels in the leaves and heads of the grassesremained relatively constant (Pritchard et al.,1964). Blue grama showed a decrease inmagnesium content with increasing maturity,but this did not occur in western wheatgrass(Rauzi et al., 1969). Halvorson and White(1981) found magnesium levels in the tillers ofwestern wheatgrass and in the vegetative tillersof green needlegrass increased with maturity,while the magnesium content of greenneedlegrass floral tillers decreased.

Grasses grown on irrigated pastures innortheast Colorado showed an increase inmagnesium content with advancing season,starting at a low of 0.21 percent in May andreaching a maximum of 0.30 percent inSeptember (Campbell, 1973). Of seven grassspecies grown on cheatgrass range in southernIdaho, only cheatgrass showed a decline inmagnesium levels with advancing season. Themagnesium concentrations in other specieswere extremely erratic (Murray Ct al., 1978).Grings et al. (1996) found an effect of live todead ratios on magnesium content of severalrange grasses growing in eastern Montana, withlive tissue concentrations being greater thandead tissue in both warm- and cool-seasongrasses. This relationship did not hold true forsedges or forbs. A similar relationship formagnesium concentrations in live and deadtissue was observed by Greene et al. (1987) forforage species in the Rolling Plains of Texas.

Magnesium bioavailability from forages hasbeen shown fairly consistently to increase withincreasing plant maturity. This had beenobserved in a variety of forage types, includingfreshly chopped tropical grasses (Perdomo etal., 1977), warm-season grass hays (Vona et al.,1984), and cool-season forages (Powell et al.,1978; Rosero et al., 1980).

The K:(Ca+Mg) ratio of forage reportedly iscorrelated to the incidence of grass tetany(Kemp and t'Hart, 1957). When this ratio wasgreater than 2.2:1, the occurrence of grasstetany was increased. Butler (1963) also found

the K:(Ca+Mg) ratio to be positively correlatedwith the incidence of tetany, although hereported ratios as low as 1.25:1 to be associatedwith occurrence of the disorder. Stuart et al.(1973) reported that the K:(Ca+Mg) ratio wassignificantly increased after a temperature rise.This increase in the ratio was due to an increasein potassium levels, while calcium andmagnesium levels decreased or remainedconstant. High dietary potassium depressesmagnesium absorption from the rumen (Greeneet al., 1983a).

Tetany-prone forages also are often high incrude protein, and it is thought that perhapsnitrogen interferes with magnesiummetabolism. Several studies have reportedincreased urinary excretion and decreasedplasma magnesium levels but no effect onabsorption in ruminants fed high nitrogen diets(Head and Rook, 1955; Moore et al., 1972).The decreased magnesium bioavailabilityassociated with grass tetany is a multi-facetedevent.

Magnesium supplementation. Supplementalmagnesium often is provided to lactating beefcows in temperate areas for the prevention ofgrass tetany. Availability of magnesium frominorganic sources does vary. Magnesium oxideis a common source of magnesium, but thebioavailability of the magnesium from thissource can vary with particle size, source, andtemperature of processing. Magnesium sulfateis a highly bioavailable source of magnesium,but it contains only about 20 percentmagnesium, so that consumption ofsupplements containing this source must berelatively high to ensure adequate magnesiumintakes. Reid et al. (1976) added magnesiumsulfate to drinking water and obtained intakesof 14 g Mg/d for wintering beef cows. Reportsof magnesium bioavailability in dolomiticlimestone range from 28 to 71 percent of that ofmagnesium oxide for cattle (Gerken andFontenot, 1967; Moore et al., 1971). Magnesitehas been found to be poorly utilized by steers(Ammerman et al., 1972; van Ravenswaay Ctal., 1989). Other sources, such as acetate,citrate, basic carbonate, chloride, and

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hydroxide forms have been found to be readilyavailable to cattle (Henry and Benz, 1995).

Since supplementation of readily fermentablecarbohydrates has been shown to improvemagnesium absorption from forage sources,providing an energy source along with amagnesium supplement may aid in theprevention of grass tetany by improvingmagnesium utilization. Additions of starch andglucose to the diet have increased magnesiumabsorption (Madsen et al., 1976) or plasmamagnesium levels (Wilson Ct al., 1969).

Magnesium fertilization has been successful atincreasing forage magnesium concentrations.In areas were fertilization is feasible, this couldbe a useful method of increasing dietarymagnesium, since several of the inorganicsources of supplementary magnesium may besomewhat unpalatable, making it difficult tomaintain adequate intakes for prevention ofgrass tetany. Forage breeders have beensuccessful at developing cultivars of cool-season grasses that have increasedconcentrations of magnesium. Mosely andBaker (1991) found a decreased incidence ofgrass tetany in lactating ewes grazing a cultivarof Italian ryegrass bred for high magnesiumconcentrations compared to a control cultivar.Utilization of cool-season forages bred for highmagnesium content holds great potential as ameans of magnesium "supplementation."

Sodium and Chlorine

Sodium and chlorine are both important tolivestock for the maintenance of osmoticpressure within cells and for regulation of acid-base balance. Sodium also plays a role inmaintenance of membrane potential and nerveimpulse transmission. Beef cattle require 0.06to 0.08 percent sodium in the diet. Lactationincreases this need to 0.10 percent. There is nodefined chlorine requirement for beef cattle,and deficiencies are not expected to occur.

Sodium and chloride levels in forages. Sodiumis not known to be essential for plant growth,

but chlorine is involved in oxygen productionin chloroplasts. Forage concentrations ofsodium can vary greatly. Butler and Jones(1973) reported pasture sodium content torange from 0.002 to 2.12 percent, with a moretypical range to be 0.05 to 1.0 percent. Minson(1990) surveyed the literature and, of 671 citedvalues for sodium in forages, found the meansto be 0.22 percent with over 50 percent of thesamples containing more than 0.15 percentsodium.

The effect of forage maturity on sodiumconcentrations has been variable. Morris(1980) reported variations in California annualgrassland ranges depending upon season.Decreasing sodium concentrations withincreasing plant maturity in some grasses havebeen observed by several researchers, whereasothers have reported no effect (Minson, 1990).Murray et al. (1978) did not observe any effectsof date of sampling on sodium concentrationsin grasses from southern Idaho rangelands, andGrings et al. (1996) found no differences insodium concentrations between live and deadtissues of several grasses in eastern Montana.Grings et al. (1996) found differences insodium content of several grasses to vary dueto the soil type on which plants were grown.Sodium content of annual bromes varied overtime, but no predictable patterns wereobserved. All forage sodium concentrationswere well below animal requirements.

Normal concentrations of chlorine in pasturehave been reported to range from 0.1 to 2.0percent of the diet dry matter. Chlorinedeficiencies are not expected to be observedunder practical conditions, and chlorine valuesof forages are reported very rarely.

Sodium and chloride supplementation. Sodiumis supplemented easily and routinely tolivestock to overcome deficiencies that mayexist. Of significance to animal nutrition in thewestern U.S. may be the sodium content ofwater, as high-saline waters often are found inarid and semi-arid areas of the world. Theaverage sodium concentration of surface watersin the U.S. is 55 mg/l, but values can range as

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high as 7,500 mg/l (NAS, 1974). Based on theaverage surface water value, beef cattle mayconsume 30 percent of their sodiumrequirement from water, and this would behigher with more saline waters. Cattle cantolerate a total soluble salt content in water ofup to 7,000 mg/liter and possibly higher,depending on the conditions.

Because livestock do exhibit a specific appetitefor salt, it often is used as a means to encouragethem to consume other supplementarynutrients, such as trace minerals. Variations inenvironmental supplies of sodium need to beconsidered in devising these strategies. If cattleare consuming high levels of saline waters, or ifthere is a prevalence of high sodium foragesbeing consumed (i.e., Atripex spp.), cattle maynot consume supplemental salt in quantitiesthat allow for desired consumption of othernutrients.

Sulfur

Sulfur is a component of several amino acidsand B-vitamins. Sulfur is required by rumenmicroorganisms for growth, and deficiencies insulfur often are reflected in decreased ruminaldigestibility, which then affects the animal'sability to utilize its feed. Rumen micro-organisms can synthesize necessary sulfur-containing amino acids, so that sulfur may besupplemented to ruminants in inorganic forms.Much of the sulfur added to ruminant dietsundergoes conversion in the rumen. It may beconverted to sulfide and then to amino acids byruminal microorganisms. Some sulfide andsulfur amino acids may be absorbed across therumen wall (Henry and Ammerman, 1995).Sulfate sulfur and sulfur amino acids areabsorbed in the intestine. Regulation of sulfurlevels in the body is intimately related toprotein metabolism.

Sulfur levels in forages. Sulfur content offorages can be expected to vary with proteincontent, because it is a component of sulfur-containing amino acids. Murray et al. (1978)found sulfur levels to decrease rapidly over the

growing season for grasses growing onrangelands in southern Idaho, with all speciesbeing below levels suggested for beef cattle(0.15 percent) by June. Henry and Ammerman(1995) reported that values for apparentabsorption of sulfur from plant materials havebeen in the 50 to 70 percent range.

Sulfur supplementation. Supplementation ofsulfur can improve ruminal fermentation whenanimals are consuming low sulfur diets. Thiscan be important when diets high in non-protein nitrogen are fed, and there is a need forsulfur for production of sulfur amino acids.Sulfur can be supplied in both inorganic andorganic forms. Elemental sulfur may be lessavailable than other forms (Fron et al., 1990).The ability of elemental sulfur to stimulateruminal fermentation compared with othersulfur sources appears to depend upon thesubstrate being fermented and appears adequateto stimulate ruminal fermentation with naturalfeedstuffs (Spears et al., 1978).

Other nutrients in the diet need to beconsidered when evaluating appropriatesupplementation levels. Boila and Golfman(1991) foimd increased methionine flows to theintestine in steers fed increased sulfur whendietary molybdenum was low, but whenmolybdenum was increased, supplementalsulfur had no influence on methionine flows.This may be related to formation ofthiomolybdates in the rumen. Thesethiomolybdate compounds prevent utilizationof sulfur by rumen microorganisms formethionine synthesis and also play a significantrole in copper metabolism.

Sulfur fertilization of pastures is practiced insome areas. Fertilization may increase thesulfur content of the forage and improvedigestibility, but at least a portion of this isrelated to increased yield and general foragequality. Greene et al. (1958) applied sulfurfertilizer to annual grasslands in the Sierrafoothills of California and observed an increasein legumes in both the standing crop and diet ofyearling steers as well as increases in thenutritive content of the species available.

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Fertilizing oat-wheat pasture with ammoniumsulfate in Texas did not improve weight gain ofheifers over fertilization with urea (Hardt et al.,1991).

Toxicities of sulfur are of concern in Westernrangeland due to associated impacts on coppermetabolism. Waters containing high levels ofsulfates exist in a number of areas, and this hasan impact on metabolism of other nutrients.Surface water sulfur concentrations in the U.S.range from 0 to 3,383 mg/L (NAS, 1974).

Macronutrient Supplementation forWestern Rangelands

Supplementary macrominerals do appear to beneeded for cattle grazing Western rangelands.Sodium and phosphorus are the macromineralsmost consistently deficient in Westernrangeland forages. Due to lack of storagewithin the body, and limited levels of sodium insome supplementary feeds, sodiumsupplementation may be needed throughout theyear. The need for magnesium is greatest inthe early spring, when the potential for grasstetany exists. There is limited information onthe economic value of potassiumsupplementation for mature grasses, but thisnutrient often is provided in necessary levelsthrough the process of providing other limitingnutrients such as protein. Sulfursupplementation should be considered whenlivestock are being provided a non-proteinnitrogen source.

Before deciding on a mineral supplement of aspecific concentration or a supplementationmethod, all environmental mineral sourcesshould be evaluated. This may involve theanalysis of water along with the analysis of allfeedstuffs. Water may contain highconcentrations of specific elements that mayact as a mineral source, can interfere withabsorption of other minerals, or can affectconsumption of supplements.

In evaluating mineral supplementation needs, itis also critical to account for minerals provided

by supplementary feed sources. Many proteinsupplements, provided during periods oflimited nutrient availability from range forages,may provide all of some minerals requiredduring this period. For example, the feeding of4 pounds of a good quality alfalfa hay to agestating beef cow during winter months wouldalso meet the requirements for all of themacrominerals with the exception of sodiumand, perhaps, sulfur. Oilseed meals, used asprotein supplements for grazing livestock, arealso good sources of macrominerals.

Supplementation Methods

Mineral supplementation can be accomplishedthrough a variety of methods, but consumptionof minerals can vary from none to well aboverequirements, and this varies with thesupplementation method used. Mineralizedsalt, either in loose form or in hard blocks, is avery common means of providing minerals onrangelands. However, consumption of mineralsin this form can be erratic, and it is difficult toensure adequate intakes. Minerals may bemixed with other feeds that improvepalatability and consumption, such as liquidsupplements or supplemental cakes, blocks, orpellets. This is most practical when nutrientssuch as protein or energy are limiting animalperformance, and the major nutrients are beingsupplemented. Addition of soluble minerals todrinking water may assure a more consistentintake of supplementary nutrients; but, this isunfeasible in areas where surface water is thewater source. Fertilization may alter the yield,digestibility, and mineral composition offorages and may be used as a means tosupplement livestock. However, this may notbe practical or economical on extensiverangelands, where water is limiting to plantgrowth or topography limits application.

Attempts have been made to provide limitingnutrients individually, with the assumption thatanimals will consume those nutrients that arelacking in the diet and will avoid those notneeded. Although consumption of individualminerals does vary, animals do not consume

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them at a level to meet nutrient demands(Burghardi et al., 1982; Muller et al., 1977;Pampetal., 1977).

Decisions about timing of supplementation canbe difficult due to variations in macromineralprofiles in time and space. The economic costof supplementation must be determined over atime scale of several years, due to variations inmineral profiles among years and the animal'sability to store some nutrients. Other factors tobe considered in developing supplementationprograms include caution in over-supplementing nutrients, due to excretion ofexcess nutrients into the environment, with thepotential for subsequent movement of nutrientsin the landscape to concentration points such aswaterways. Improper balancing of minerals ina supplement can impact the supplementationprogram negatively by limiting effectiveness ofminerals prevented from absorption orprevented from their physiological actions byother minerals.

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NRC. 1996. Nutrient requirements of beefcattle. Seventh Revised Ed. NationalAcademy of Sciences-NationalResearch Council. Washington, DC

Pamp, D.E., D.E. Goodrich, and J.C. Meiske.1977. Free choice minerals for lambsfed calcium or sulfur-deficient rations.J. Anim. Sci. 45:1,458-1,466.

Perdomo, J.T., R.L. Shirley, and C.F. Chicco.1977. Availability of nutrient mineralsin four tropical forages fed freshlychopped to sheep. J. Anim. Sci.45:1,114-1,119.

Powell, K., R.L. Reid and J.A. Balasko. 1978.Performance of lambs on perennialryegrass, smooth bromegrass,orchardgrass, and tall fescue pastures.II. Mineral utilization, in vitrodigestibility and chemical compositionof herbage. J. Anim. Sci. 46:1,503-1,514.

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Pritchard, G.1., W.J. Pigden, and L.P. Folkins.1964. Distribution of potassium,calcium, magnesium, and sodium ingrasses at progressive stages ofmaturity. Can. J. Plant Sci. 44:318-324.

Rauzi, F., L.I. Painter, and A.K. Dobrenz.1969. Mineral and protein contents ofblue grama and western wheatgrass. J.Range Manage. 22:47-49.

Reid, R.L., G.A. Jung, and C.F. Gross. 1976.Grass tetany as a metabolic problem- inthe eastern United States. In: HillLands, Proc. of an Intern. Symp. J.Luchok, J.D. Cawthon and M.J.Bresling (eds.). West Virginia Books,Morgantown. pp. 640-648.

Rosero, O.R., R.E. Tucker, G.E. Mitchell, andG.T. Schelling. 1980. Mineralutilization in sheep fed spring forages ofdifferent species, maturity, and nitrogenfertility. J. Anim. Sci. 50:128.

Spears, J.W., D.G. Ely, and L.P. Bush. 1978.Influence of supplemental sulfur on invitro and in vivo microbial fermentationof Kentucky 31 tall fescue. J. Anim.Sci. 47:552-560.

Stuart, D.M., H.F. Mayland, and D.L. Grunes.1973. Seasonal changes in trans-aconitate and mineral composition ofcrested wheatgrass in relation to grasstetany. J. Range Manage. 26:113-1 16.

Thomas, G.W. andB.W. Hipp. 1968. Soilfactors affecting potassium availability.In: The role of potassium in agriculture.V.J. Kilmer, S.E. Younts, and N.C.Brady (eds.) Amer. Soc. Agron., CropSci. Soc. Amer., Soil Sci. Soc. Amer.,Madison, WI pp. 269-291

van Ravenswaay, R.O., P.R. Henry, C.B.Ammerman, and R.C. Littell. 1989.Comparison of methods to determinerelative bioavailability of magnesium inmagnesium oxides for ruminants. J.Dairy Sci. 72:2968

Vona, L.C., G.A. Jung, R.L. Reid and W.C.Sharp. 1984. Nutritive value ofwarm-season grass hays for beef cattleand sheep; digestibility, intake, andmineral utilization. J. Anim. Sci.59:1,582.

Wilson, G.F., C.S.W. Reid, L.F. Molloy, A.J.Metson, and G.W. Butler. 1969.Influence of starch and peanut oil

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supplements on plasma magnesium,calcium and phosphorus levels ingrazing dairy cows. New Zealand J.Agr. Res. 12:467.

Wise, M. B., A. L. Ordoveza and E. R. Barrick.1963. Influence of variations in dietarycalcium:phosphorus ratio onperformance and blood constituents ofcalves. J. Nutr. 79:79-84.

Introduction

Inadequate energy and (or) protein supply hasbeen recognized as factors limiting beef cattleproduction when range forages undergodormancy. However, some investigators haveobserved suboptimal animal performance withadequate supply of these macronutrients.Under these conditions, insufficient supply ofthe micronutrients may be involved becauseruminants, like nonruminants, must receive allthe essential nutrients in optimum quantities inorder to maintain good health, to grow, and toreproduce at their maximum potential. Forexample, deficiencies in the fat-solublevitamins, primarily A and E, are apt to beapparent when cattle have consumed dormantor low-quality stored forages for extendedperiods of time. A large body of researchconcerning vitamin nutrition of ruminants hasbeen conducted over the last 60 years. Theintent of this chapter is to focus on literaturedealing with vitamins, which may impactproduction of ruminants consuming forages.

Vitamin A

California researchers (Guilbert and Hart,1934; 1935) were among the first to investigatethe vitamin A status of range cattle. Theyconcluded that under normal conditions, rangecattle could accumulate adequate reserves ofvitamin A during the green season to meet theirrequirements during the dry season, when manyforage plants are quiescent. However, theyrecommended supplementing cattle with goodquality alfalfa hay during the dry season as aprophylactic measure against vitamin Adeficiency and to prevent poor reproductiveperformance. This early research alsodemonstrated that 67 to 93 percent of the bodyvitamin A stores are found in the liver.

VITAMIN NUTRITION OF CATTLE CONSUMING FORAGES

Bret W. HessDepartment of Animal Science,

University of Wyoming, Laramie, WY 82071

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Guilbert and Hart sparked an epoch to be filledwith many reports on forage vitamincomposition, vitamin digestion andmetabolism, and vitamin supplementation ofruminants consuming forages.

Vitamin A levels in plant material. Thebiologically active form of vitamin A (all-trans-retinol) is present in plants as precursorsknown as carotenoids. The most active of thesecarotenoid precursors is J3-carotene, which, asearly as the 194 Os, was demonstrated to be themajor carotenoid of plant origin. Kemmerer etal. (1942) showed that 61 to 94 percent of thecarotene of dried forages and 94 to 98 percentof fresh grasses was 13-carotene. This samelaboratory (Kemmerer et al., 1944) found the 13-carotene content of dried grasses to be 72.7percent and the total 13-carotene equivalent of77.1 percent of the total carotene.

The amount of 13-carotene in forages variesaccording to plant species, maturity, harvesting,processing, and storage conditions. Hamiltonet al. (1956) collected samples of Indianricegrass (Oryzopsis hymenoides), squirreltailgrass (Sitanion hystrix), and several browseplants (Artemisia spp.; A triplex spp.;Chrysothamnus spp.; Eurotia lanata;Gutierrezia sarothrae; Leptodactylon pungens;Sarcobatus tridentata; Tetradymia inermis) inNovember (beginning of dormancy) and April(before regrowth) at a site located on the RedDesert of Wyoming. Browse plants hadrelatively high levels of carotene, even in April(avg 45.5 ppm). The two samples of grasseswere lowest in carotene content (avg 14.9 ppm)at both collection dates. The carotene contentof the grasses and some plants having dryleaves or stems, such as broom snakeweed(Gutierrezia sarothrae) decreased markedly(30 to 50 percent) between November and

April. It was noted that the presence of a smallnumber of green basal blades on the curedgrasses presumably increased (approximately45 percent) the carotene content of the samplescollected in November. There was not anappreciable change in the carotene content ofmost of the other browse plants studied.Furthermore, the carotene content of the leavesand twigs differed for most browse plants.Sagebrush (Artemisia spp.), shadscale, andsaltbush (Atriplex spp.), and winter fat (Eurotialanata) had greater carotene content in theleaves, buds, and tips; whereas, big rabbitbrush(Chrysothamnus pumilus), broom snakeweed(Gutierrezia sarothrae), granite gila(Leptodaclylon pungens), and greasewood(Sarcobatus vermiculatus) had higher carotenecontent in the stems. Therefore, consumptionof plant species and (or) specific plant parts, aswell as mature forage, could impact greatlyvitamin A status of grazing livestock.

Seasonal and regional conditions can influencedietary 13-carotene and subsequent vitamin Astatus of cattle. Forage samples taken fromnine beef cattle ranches located in four soilorder regions of Florida averaged 17.6 ppmcarotene in the wet season (September toOctober) and 1.2 ppm carotene in the dryseason (February to March) (Kiatoko et al.,1982). Liver vitamin A stores of the cattledoubled during the wet season, reflectingseasonal differences in forage caroteneconcentrations. Forage carotene content rangedfrom 6.0 to 16.3 ppm depending on the region.Likewise, liver vitamin A concentrations werelowest in cattle residing in the region withlowest forage carotene content. At a study sitelocated in the foothills of the Sierras, nearMarysville, California, Ighiesias and Morris(1982) found a positive correlation (r = 0.70)between cow plasma carotene and rainfall.These range cows had decreased liver vitaminA concentrations as the year progressed, whichis an indication of vitamin A mobilizationbefore the annual growing season.

Harvested forages are easily obtainable sourcesof feed that often are used to sustain livestockduring periods of low standing crop

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availability. Holding such hays in reserve forperiods up to several years may deplete thecarotene content. Schubert et al. (1956)analyzed 61 samples of stored native meadowhay harvested in the Northern Great Basin. Theforage composition of the hay from nativeflood meadows was 50 percent sedges (Carexspp.), 40 percent rushes (Juncus spp.), and10 percent grass and forb mixtures. Resultsfrom samples collected from the Squaw ButteStation indicated that the initial year's declinein carotene content of stacked hay is60 percent. Of the remaining amounts, anaverage additional 75 percent deterioration wasnoted for the second year of storage. Thecarotene content for the newly cured hayranged from 35 to 44 ppm, which iscomparable to alfalfa hay (NRC, 1984). Inanother paper by the Oregon State researchers(Wheeler and Sawyer, 1956), carotene contentof the same native hays ranged from 1.3 to 2.4ppm at the time of harvest. The hay in thesecond study was bleached by leaving it in theswath for 3 to 6 weeks or until the green colorhad disappeared. Carotene content ofdehydrated alfalfa dropped to 67, 50, 47, 43,and 37 percent of initial storage values at 3, 5,7, 9, and 11 months, respectively (Blosser etal., 1950). In Blosser's study, wilted and sun-cured alfalfa had 75 and 36 percent,respectively, of the carotene content of thedehydrated material at the time these materialswere stored. Carotene levels of dehydratedalfalfa were much lower after 5 months ofstorage during the warmer months of summercompared to the cooler months of autumn(Blosser et al., 1950). These studiescollectively demonstrate the importance ofproper harvesting, processing, and storing offorages in order to retain high levels ofcarotene.

Functions and utilization of vitamin A. Muchof the interest in vitamin A's function in cattlehas centered around its role in vision,reproduction, and immunity. Dietary 13-carotene can elevate peripartal concentrationsof blood 13-carotene, enhance host defensemechanisms by potentiating lymphocyte andphagocyte function, and decrease the incidence

of certain reproduction disorders (Michal et al.,1994). 3-carotène (Krinsky, 1989; Michal etal., 1994) and vitamin A (Miller et al., 1993)have been shown to be effective antioxidantsand potent quenchers of free radical species.Additionally, vitamin A and (or) n-carotenealso seem to be important factors in reducingthe incidence of retained placentas (Chew et al.,1977) and metritis (Michal et al., 1994).Because of vitamin A's effectiveness inmaintaining epithelial integrity in addition to itsaforementioned functions, supplementation ofrange livestock may be advisable, particularlywhen range forage has gone dormant.

Deprivation of optimal carotene intake forextended periods of time may impair theanimal's ability to utilize vitamin A.Inappreciable increases in liver vitamin Astores were noted when cattle were realimentedto normal carotene intake or given repeatedinjections of vitamin A following suboptimalcarotene intake (Byers et al., 1955). Erwin etal. (1957) noted a marked increase in livervitamin A stores when 15 mg of carotene/45 kgof body weight (BW) was dosed intraruminallyevery other day for 10 days only if steers werenot previously depleted of vitamin A. Grifo etál. (1960) corroborated earlier work andsuggested that the duration of deficientcarotene intake needs to be considered as avariable in evaluation of the vitamin A status ofcattle subsequently fed carotene.

Diminished ability of cattle to utilizesupplemental vitamin A often has beenattributed to ruminal degradation. A number ofpapers reviewed by Ullrey (1972) indicated thatappreciable amounts (40 to 70 percent) ofcarotene or vitamin A are degraded in therumen. However, more recent evidence wouldindicate that ruminal degradation of vitamin Ais not exceedingly high for cattle consumingdiets high in forage. Disappearance of vitaminA during a 24-hour in vitro ruminalfermentation system was 16 and 19 percentwhen donor steers were fed hay and straw,respectively (Rode et al., 1990). Weiss et al.(1995) demonstrated that 80 percent of addedretinol was recovered after a 24-hour

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incubation period in fluid collected fromruminally cannulated cows consuming an 80percent forage diet (20 percent corn silage and60 percent grass hay). An alternativeexplanation for decreased storage of vitamin Ain the liver following depletion of body storescould be related to reduced carrying capacity ofthe blood and (or) metabolism of vitamin Aelsewhere in the body.

Wing (1969) reported that the apparentdigestibility of carotene, in various forages fedto dairy cattle, averaged about 78 percent.Variables which influenced carotenedigestibility included month of forage harvest,harvesting method, and plant species. Carotenedigestibility was generally higher in forages ofbetter quality. Therefore, the possibility ofavitaminosis A in cattle grazing dormant rangeor lower quality forages is augmented by areduction in digestibility of carotene.

Vitamin A supplementation. Erwin Ct al. (1955)demonstrated that steers consuming a diet ofpredominantly wheat straw had reduced liverstores of vitamin A compared to thoseconsuming a diet consisting primarily of alfalfameal. Feeding 16,000 IU additional vitamin Adaily to cows before calving followed by40,000 lU/day at the beginning of the calvingseason increased conception rates 11 percentand decreased calf morbidity approximately 50percent (Meacham et al., 1970). Wheeler andSawyer (1956) reported that night blindnessdeveloped in 28-day-old calves from cows notsupplemented with vitamin A and fed nativemeadow hay low in carotene (<5 ppm) for 1year. Steers consuming supplemental vitaminA (5,000 lU/day) in a finely-ground saltmixture stored twice as much vitamin A in theirlivers over the winter months compared to non-supplemented steers (Page et al., 1958).Likewise, feeding 20,000 Hi of vitamin A dailyfor 120 day to steer calves consuming nativemeadow hay increased plasma concentrationsand liver stores of vitamin A (Wallace et al.,1964).

Baker et al. (1954) found that supplementalcarotene during lactation was essential for

normal vitamin A nutrition of calves, regardlessof liver vitamin A stores at parturition. Plasmavitamin A in calves is low at birth, increasesduring the first week, and stabilizes thereafter(Meacham et al., 1970). Furthermore,concentrations of 13-carotene and vitamin A inthe blood of cows decreased during theperipartal period (Johnston and Chew, 1984;Goff and Stabel, 1990). These collectivefindings are associated with vitamin A andcarotene being components of colostrum andmilk (Meacham et al., 1970; Johnston andChew, 1984; Weiss et al., 1994).

Wheeler et al. (1957) reported that calvesnursing cows on restricted carotene intakes (< 5ppm) had plasma vitamin A levels of 2 to 14.tg/dL. In calves nursing cows grazing springpasture, they found levels of 10 to 30 j.tg/dL. Itis not known how much pasture intakecontributed to vitamin A status of the calves inthe study of Wheeler et al. (1957).Nonetheless, a single injection of vitamin A(6,000,000 IU) in peripartal cows has increasedcalf survival to weaning (Meacham et al.,1970).

Supplemental vitamin A may not always beneeded when cattle are grazing rangelandsduring suspected dormancy. Plasma vitamin Alevels of neonatal calves were not affected(29.1 vs. 29.9 pg/dL) by supplementing damswith vitamin A (Meacham et al., 1970). Inanother trial, Meacham et al. (1970) reportedthat calves injected with 300,000 IU of vitaminA at birth did not show increased plasmavitamin A concentrations nor increased growthperformance compared to calves not receivinginjectable vitamin A. Similarly, feedingvitamin A (16,000 lU/day during late gestationand 40,000 lU/day during early lactation) didnot prove to be beneficial in a follow-up trial ofMeacham et al. (1970).

After 5 years of data collection, Washburn etal. (1952) concluded that Eastern Coloradorange maintained its carotene content for8 months of the year. Cattle grazing sagebrush-bunchgrass range from May to Septemberfollowed by meadow aftermath until

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December, followed by hay low in carotene (<2.5 ppm) from December to early May, did notshow signs of vitamin A deficiency (Wheelerand Sawyer, 1956). Cows grazing southernNew Mexico rangeland consumed plantsadequate in carotene to maintain blood 13-

carotene and vitamin A levels aboverequirements (Watkins and Knox, 1953). Thedominant grass species, black grama, alongwith browse plants were suspected to haveprovided a wintertime source of carotene.Despite the apparent mobilization of livervitamin A in the study of Ighlesias and Morris(1982), liver biopsy data indicated that cowswere not deficient in vitamin A at any point intime. On a practical basis, however, no morethan 2 to 4 months of protection can beexpected from stored vitamin A (NRC, 1996).Therefore, supplemental vitamin A, feed gradeor ingestible, is recommended to preventpotential problems with productive efficiencyof cattle when feed sources are most apt to below in carotene.

Vitamin E

Vitamin E status likely will follow the sametrend as that of vitamin A when cattle areconsuming dormant rangeland or harvestedforages. Kiatoko et al. (1982) showed thatseasonal nutrient differences in forages werereflected in plasma levels of vitamin E. Plasmavalues were 42 percent higher in vitamin Econcentration during Florida's wet seasoncompared to the dry season. Furthermore,forage carotene content was positivelycorrelated (r = 0.56) with plasma vitamin Econcentration. This is not surprising, becauseboth of these fat-soluble vitamins decrease inconcentration as forages undergo dormancy andcan function similarly in the animal's body.

Vitamin E levels in forages. Vitamin E is ageneric term used for tocopherol compounds.The biological reference for vitamin B activityis a-tocopherol. In a review of 455 publishedarticles, Dicks (1965) reported that the majorityof tocopherol in forage matter is a-tocopherol.Therefore, vitamin E and a-tocopherol will be

used interchangeably throughout the remainderof this section.

The level of a-tocopherol in forage cropsgenerally decreases as plants mature. In theirreview of the literature, Kivimae and Carpena(1973) found that concentrations of a-tocopherol in alfalfa and timothy (Phleum spp.)declined 20 to 65 percent depending onwhether the crop was harvested in the late-vegetative or full-flowering stage ofdevelopment. Brown (1953) reportedextraordinarily large differences ina-tocopherol concentrations of vegetativeversus fully mature grasses. Concentrations ofvegetative grass samples ranged from 22.1 to30.3 ppm, collectively. Upon maturity, a-tocopherol levels dropped 79, 89, 87, and90 percent for meadow fescue (Festucapratensis), orchardgrass (Dactylis glomerata),timothy (Phleum pratense), and perennialryegrass (Lolium perenne), respectively.Leaves also were shown to contain three to fourtimes more a-tocopherol than the stems(Brown, 1953; Dicks, 1965). As little as 33 to37 percent loss in vitamin E can be expectedfrom green-up to maturity for certain forages,e.g., sudangrass (Sorghum bicolor) andwheatgrass (Agropyron spp.) (Dicks, 1965).However, long term curing may decrease a-tocopherol levels even further.

The concentration of vitamin B is much higherin fresh grass than in harvested and processedforages. Canadian researchers (Hidiroglou etal., 1994) noted that a-tocopherolconcentrations of first-cutting alfalfa/timothydeclined from 70 ppm to 35 and 15 ppm fromthe time of harvest for silage and hay,respectively. Average-quality [8.7 percentcrude protein (CP); 54 percent total digestiblenutrients (TDN)] grass hay had 12 ppmvitamin E in a study conducted at theUniversity of Florida (Hidiroglou et al., 1988).Alpha-tocopherol content averaged 9.1 JIJ/kg(as fed) in poor-quality (nutrient analyses notgiven), overly mature bermudagrass (Cynodondactylon) hay (Njeru et al., 1995). The studiesreviewed by Kivimae and Carpena (1973)

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indicated that high moisture content andprolonged exposure to heat resulted insignificant losses of a-tocopherol. Losses wereheightened as storage duration increased.Researchers at Colorado State University(Nockels et al., 1996) reported that year-oldbrome and crested wheatgrass hay contained8.1 IU of a-tocopherol/kg of DM.Supplementing vitamin B to cattle consuminglow-quality range or harvested forages as aprecautionary measure may be warranted dueto the low levels of a-tocopherol in theseforages.

Functions and utilization of vitamin E.Vitamin B is known primarily for its action asan antioxidative component of cell membranesthat prevents peroxidative damage to the cellmembrane and membranes of subcelluiarorganelles by free radicals (Burton and Ingold,1989). The antioxidative role becomes veryimportant during the immune response, whenneutrophils produce large quantities ofsuperoxide and hydrogen peroxide frommolecular oxygen to destroy foreign organisms(Ross, 1977). Peroxidative inactivation ofsteroidogenic enzymes also can impairreproduction (Miller et al., 1993). Tissuecontent of a-tocopherol is important inprotecting cattle from nutritional musculardystrophy or white muscle disease (McDowell,1989) and promoting increased productivity byenhancing immune (Reddy et al., 1986;Nockels, 1988) and reproductive (Shigemoto etal., 1980; Harrison et al., 1984) functions.

Vitamin B, like vitamin A, is not metabolizedor oxidized extensively in the gastrointestinaltract of cattle consuming forages. Alderson etal. (1971) found that disappearance of vitaminE was only 8 percent in samples collected fromabomasally cannulated steers fed an alfalfahay:corn grain diet (80:20). Using radiolabeleda-tocopherol, Astrup et al. (1974) reported nosignificant degradation after a 24-hour in vitroincubation with ruminal contents from a fastedsheep fed an alfalfa chaff:oats (1:1) diet. Datafrom studies conducted in the 1 990s suggestthat ruminal metabolism of vitamin B isnegligible for all forage (McDiarmid et al.,

1994), 50 percent forage (Weiss Ct al., 1995),and high concentrate (Leedle et al., 1993) diets.

Roquet et al. (1992) demonstrated that steershad much lower concentrations of vitamin E inthe plasma when supplementala-tocopherol was dosed directly into theduodenum compared to an intraruminal dose.They suggested that lower uptake of esterifiedvitamin E given directly in the duodenum was aresult of insufficient time for emulsificationpreceding absorption. This seems to be areasonable explanation, because cows fedsupplemental fat, which would enhanceemulsification capacity, have increased plasmaconcentrations of a-tocopherol (Weiss et al.,1994). Beef cattle would not be expected toconsume quantities of fat sufficient to bolsterlevels of plasma a-tocopherol. However, thebioavailability of acetylated a-tocopherol canbe increased when combined with D-a-tocopherol polyethylene glycol succinate(Hidiroglou et al., 1992).

It has been suggested that < 1.0 to 1.5 .tg ofa-tocopherol/mL in serum can be cOnsidereddeficient for ruminants (McMurray and Rice,1982). Adams (1982) set the minimal plasmaa-tocopherol level required for cattle at 3.0 to4.0 j.Lg/mL, between 2.0 to 3.0 pg/mL asmarginal, and < 2.0 j.ig/mL as deficient. Thereis inconsistency, however, concerning theadequacy of relying solely on serum or plasmaa-tocopherol concentrations as an index ofvitamin E status. The liver is the major storageorgan for a-tocopherol and helps maintainplasma a-tocopherol levels under short terminadequate intake of vitamin E (Hidiroglou etal., 1988).

According to Charmley et al. (1992),circulating levels of vitamin E in differentclasses of cattle seem to be influenced by bloodlipids, making serum a-tocopherol anunreliable index of vitamin E status. Weiss etad. (1994) concluded that when concentrationsof plasma lipids are different because of diet,concentrations of a-tocopherol in the plasmashould be expressed on a lipid basis. These

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researchers suggested that elevation of theamount of a-tocopherol in plasma relative toblood lipid is necessary to increaseconcentrations of a-tocopherol in neutrophils.Others (Pudelkiewicz and Mary, 1969)suggested that when dietary vitamin Econcentrations are kept constant long enoughfor stabilization of plasma and liver a-tocopherol, a blood sample might provide asatisfactory index of the vitamin E state of theanimal. Recent data on yearling beef heifersindicated that both serum and liver a-tocopherol levels respond to incrementalsupplementation and withdrawal of vitamin E(Njeru et al., 1995). Therefore, it would appearas if serum ec-tocopherol concentrations can beused to indicate vitamin E status of cattle fedforages as the primary dietary ingredient.

Vitamin E supplementation. Cattle consumingpredominantly low-quality range or harvestedforages are not likely to maintain blood a-tocopherol at the previously suggested levels.Mean plasma vitamin E concentrationdecreased from 3.3 to 2.3 J.Lg/rnL between thewet season to the dry season in the study ofKiatoko et al. (1982). Serum a-tocopherolvalues were 1.3 pxg/mL for Holstein cows fedorchardgrass hay and 1.8 kg/day of grainduring the last trimester of pregnancy (Lynch,1983). Plasma concentration of a-tocopherolwas 1.4 pg/mL for beef cows consuming 2 kgof average-quality grass hay (12 ppm vitaminB) and a barley-soybean meal mixture adlibitum (Hidiroglou et al., 1988). Beef heifersfed bermudagrass hay (9.1 lU/kg of vitamin B)and 1.8 kg of a corn-based supplement for 28days had plasma a-tocopherol levels of1.8 ig/mL (Njeru et al., 1995). Beef cows fedalfalfa/timothy hay (15 ppm) at ad libitumintake beginning 5 months before calvingthrough 30 days into lactation had plasmaa-tocopherol levels of 2.6 j.tg/mL; plasmaa-tocopherol concentrations were 3.4 j.ig/mLfor cattle fed silage (30 ppm) harvested at thesame time and from the same field (Hidiroglouet al., 1994). Results of these studies can beinterpreted to suggest that cattle consumingforages with a-tocopherol concentrations

below 15 ppm are suspect for marginal vitaminB deficiency. To compound the marginaldietary deficiency many Western beef cattlemay experience, vitamin E concentration in theblood decreases during the peripartal period(Goff and Stabel, 1990; Weiss et al., 1990b;Zobell et al., 1995). Thus, supplementalvitamin E may be required to maintain blood a-tocopherol at desirable levels.

A single injection of 3,000 IU of vitamin E i.m.21 days before expected calving increasedplasma a-tocopherol concentrations an average5.6 percent through 30 days into lactation(Hidiroglou et al., 1994). Hidiroglou andLaflamme (1993) reported that maximumplasma vitamin B concentration occurs24 hours after i.m. administration, dropping tonear initial values within 10 days after theinjection. This finding offers an explanationfor the results of Hidiroglou et al. (1994), whoobserved no effect on plasma concentrations ofoc-tocopherol 10 days after administration.Moreover, biweekly injections would benecessary to sustain blood vitamin E atdesirable levels.

Feeding supplemental vitamin E is an effectivealternative to the more labor intensiveinjectable route. Cattle receiving 1,000 IU in25 g of molasses showed a progressive increase(1.4 to 6.7 pg/mL) over a 28 daysupplementation period (Hidiroglou et al.,1988). Vitamin E reached the minimal levelrequired (Adams, 1982) between day 1 and 7.Njeru et al. (1995) noted a rapid increase inserum a-tocopherol during the first 3 days ofdaily supplementation (500, 1,500, and 3,000IU of vitamin E/animal). Serum a-tocopherolreached the minimal desirable levels by day 14for all supplemental treatments and continuedto increase at diminishing rates to 28 days ofsupplementation. Upon withdrawal of thesupplement, serum a-tocopherol levelsdeclined rapidly, reaching initial levels (1.8pg/mL) within 28 days, suggesting continuoussupplementation is required to maintain serumvitamin E at the minimal concentrationsoutlined by Adams (1982).

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Dietary supplementation with vitamin E atlevels above those recommended as nutritionalrequirements may allow for optimal immuneresponse (Tengerdy, 1990) and promote calfhealth (Zobell et al., 1995). When vitamin Ewas injected (6,000 JJJ) into peripartum dairycows, killing ability of neutrophils wascorrelated to concentrations of a-tocopherol inneutrophils (Hogan et al., 1992). Percentage ofneutrophils phagocytizing also has beenenhanced in response to 1,000 IU ofsupplemental vitamin E in the diet (Weiss etal., 1994). Reddy et al. (1986) observed higherbovine herpes virus antibody titers in calvessupplemented with 125 IU of vitamin E/daythan in control calves. Feeding vitamin E(1,400 Hi/day) in conjunction with Brucellaabortus strain 19 vaccine may have enhancedthe levels of total and 1gM natural antibody toSalmonella typhimurium of beef heifers feddirect-cut orchardgrass silage (Nemec et al.,1990). Aipha-tocopherol has been shown toenhance 1gM production significantly whenadded to cells isolated from Jersey cows andcultured in pokeweed mitogen (Stabel et al.,1992). In another study, Reddy et al. (1987)observed that 1-day-old calves receiving 2,800mg of vitamin E as dl-a-tocopherol/week for12 weeks had significantly higher serum 1gMconcentrations. However, supplyingsupplemental vitamin E to the calf directly maynot be necessary.

The incidence or severity of vitamin B-responsive disease in calves seems to be -

influenced by placental and mammary glandtransfer of a-tocopherol (Hidiroglou et al.,1972). Calves must receive dietary vitamin B,because placental transfer of a-tocopherol isvery limited (Hidiroglou, 1989; Van Saun etal., 1989); consequently, levels of vitamin B inneonatal blood are 1.0 pg/mL or less (Reddy etal., 1985; Hidiroglou et al., 1994). Maternalsupplementation with vitamin E can providepartial protection for the offspring fromnutritional muscular dystrophy (white muscledisease). Supplementing approximately1,000 Hi/day of vitamin E during the peripartalperiod significantly increased concentrations ofa-tocopherol in the colostrum (Weiss et al.,

1994) and colostral fat (Weiss et al., 1990a;1992) compared to that of dairy cows not fedsupplemental vitamin E. Feeding an additional1,000 IU of a-tocopherol to beef cattle between60 to 100 days prepartum increased vitamin Ein the colostrum from 8.8 to 12.2 tg/mL(Zobell et al., 1995). Calf plasma vitamin Econcentrations postpartum (48 hours) were37.5 percent greater when dams consumed anadditional 1,000 IU of a-tocopherol. Others(Parrish et al., 1950; Hidiroglou, 1989) haveshown that pre- and postpartum maternalvitamin E supplementation results in a rapidincrease in serum oc-tocopherol concentrationof neonates following consumption ofcolostrum. Furthermore, plasma concentrationsof vitamin B in the neonate can be maintainedabove Adams' (1982) minimal level if maternalsupplementation continues into the early stagesof lactation (Njeru et al., 1994). Therefore,vitamin E supplementation is recommended forbrood cows consuming poor-quality forage latein gestation through early lactation.

Vitamin D

Vitamin D is a pro-hormone formed byultraviolet irradiation of skin (D3) or plantmaterial (D2). A general scheme of vitamin Dmetabolism and the factors that influencevitamin D activity were presented by Littledikeand Goff(1987). Vitamin D enters the bloodfrom the gut or the skin and rapidlyaccumulates in the liver and adipose tissue. Inthe liver, vitamin D is converted to 25-hydroxyvitamin D [25-(OH)D]. Thismetabolite is the major circulating form ofvitamin D in animals under normal conditionsand serves as the precursor of the other vitaminD metabolites (Horst and Liftiedike, 1982).Once 25-(OH)D reaches the kidney, it isconverted to the most biologically active form,1,25-(OH)2D. The role of 1,25-(OH)2D is tomaintain normal blood Ca and P concentrationsby facilitating Ca and P transport across theintestinal brush border (Wasserman and Taylor,1976) and enhancing bone resorption (DeLuca,1984).

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Vitamin D levels in forages. According toHorst et al. (1981), vitamin D2 in naturalfeedstuffs supplies the majority of vitamin D inruminant animals. In 1949, Wallis et al.reported on the vitamin D2 content of 66forages from different parts of the country. Inthis report, vitamin D2 values of sun-curedroughages ranged from 26.7 to 638 lU/kg.Dehydrated forages had vitamin D2 levelsroughly 19 percent that of sun-cured forages.Blosser et al. (1950) noted that the vitamin D2value for dehydrated alfalfa was 62 percent ofsun-cured hay harvested at the same time.Despite lower concentrations of vitamin D2 incertain forages, cattle housed outside are notsuspected to be deficient in vitamin D.

Vitamin D supplementation. In all but theextreme Northern latitudes, sunlight stimulatessufficient endogenous production of vitamin D3(Littledike and Goff, 1987). Smith and Wright(1984) concluded that the synthesis of thevitamin D3 in the skin plays a dominant role invitamin D status of grazing animals. Others(Hidiroglou et al., 1985; Hidiroglou, 1987)demonstrated a significant increase in plasmaD3 and 25-OHD3 concentrations followingexposure to UV irradiation. Indeed, vitamin Dstatus is improved more effectively byincreasing exposure to the natural sunlightspectrum than by supplementing with highdietary levels of D3 (Hidiroglou and Karpinski,1989). Hidiroglou and Karpinski (1989) notedthat plasma 25-OHD3 concentrations increasedcontinuously and plateaued between day 65 to75 at about 21 ng/mL when vitamin D3 wassupplied in the diet. Exposure to UVirradiation for 10 hours/day increased 25-OHD3concentrations from 7.5 to 29.6 ng/mL, whichplateaued about 3 weeks sooner than dietaryvitamin D3 treatment. Holick (1987) surmisedthat prolonged exposure to IJY does notsignificantly increase the previtamin D3concentration above about 15 percent of theinitial provitamin concentration. Therefore,cattle under normal range conditions would notbe expected to exhibit vitamin D intoxificationunless overzealous use of injectablepreparations is common practice. Parenteraladministration of 15 million IU of vitamin D3

in a single dose caused toxicity and death inmany pregnant dairy cows (Littledike andHorst, 1982).

Injectable preparations given at moderate levelsshould not cause ill effects. Nevadaresearchers (Bradfleld and Behrens, 1968)showed an increase in fall pregnancy of11.0 and 12.9 percent for beef cattle injectedwith vitamin A, D, and E and bred under rangeand pasture conditions, respectively. VitaminD concentration in the preparation ranged from2,500 to 100,000 ITJ/rnL It is difficult toattribute these effects to vitamin D, becausevitamin A (100,000 to 250,000 IU/mL) andvitamin E (30 to 50 mg/mL) also were includedin the injectable preparations. In light of theprevious discussion, vitamins A and Bpresumably would have a greater impact onreproductive performance. Nonetheless, Milleret al. (1993) hypothesized that nutrientsrequired for antioxidant defense may beessential for production of 1 ,25-(OH)2D.Hence, a deficiency in vitamin A or E or bothcould potentiate a vitamin D deficiency.Additional research is needed to substantiatethis possibility, but supplementing all three ofthese fat-soluble vitamins may be warranted forhigh producing beef cattle.

Vitamin K

The ruminal microorganisms generallysynthesize and supply vitamin K in amountssufficient to meet the ruminant animal'srequirements. Supplemental vitamin K usuallyis justified only when cattle are suspected tohave consumed sufficient quantities of vitaminK antagonists. Consumption of natural vitaminK antagonists can be a problem in certainregions in the U.S.

Sweetclover [Melitotus officinalis (yellow-flowered) and Melilotus alba (white-flowered)]is a biennial legume commonly grown in theNorthern Plains (loveland and Townsend,1985). Sweetciover produces a distinct,vanilla-like odor due to the presence ofcoumarin in the plant. Metabolism of coumarin

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by fungi during the molding process producesthe vitamin K inhibitor, dicumarol. Becausedicumarol antagonizes vitamin K, an essentialcomponent of the blood clotting process,feeding moldy sweetciover hay to cattle maycause hemorrhage and uncontrollable bleeding.Typical early signs of sweetciover poisoninginclude hematomas in subcutaneous tissues ofthe ventral cervical area, ventral abdominalwall, and muscles of the hind limb, andhemorrhage in carpal and (or) tarsal joints(Aistad et al., 1985).

Successful treatment of dicumarolintoxification has been demonstrated withinjectable vitamin K1 (Aistad et al., 1985) andvitamin K3 (Radostits et al., 1980). However,responses to vitamin K therapy have beensomewhat dependent on differences indicumarol source and dosages. Therefore,prevention (avoiding moldy sweetciover hay) isperhaps a better alternative than treatment.

B vitamins

Microbial synthesis of the B vitamins in therumen is thought to satisf' the ruminant'srequirements. Wegner et al. (1940; 1941)reported that thiamin, niacin, riboflavin, biotin,pantothenic acid, and pyridoxine weresynthesized in heifers fed natural and semi-purified diets. Agrawala et al. (1953) were thefirst to establish that the B vitamin self-sufficiency exhibited by ruminants was due tothe synthesis of the vitamins by ruminalmicroorganisms. Despite early indications of Bvitamin self-sufficiency, many subsequentinquiries have been made regarding theadequacy of B vitamin production by theruminal microbes.

Increasing organic matter (OM) digestion in therumen via dietary manipulations has increasedB vitamin production in the rumen (Hollis etal., 1954; Kon and Porter, 1954; Sutton andElliot, 1972). As early as 1944, Lardinois et al.recognized that production of B vitamins wasnot maximized in the absence of readilyfermentable carbohydrate. Conrad and Hibbs

(1954) found that grain additions to maturegrass hay diets increased ruminal quantities ofB vitamins. Likewise, addition of starch toinoculum collected from ruminally cannulatedsteers fed alfalfa and timothy hay increased B-vitamin production in an artificial rumen (Huntet al., 1952; 1954). Work of Miller et al.(1986) corroborated the conclusions of Conradand Hibbs (1954), who stated that ruminalsynthesis of B vitamins was not affected byfeeding different ratios of grain to hay whenhigh-quality legume was fed. Thus,supplementation with B vitamins does notappear to be necessary if cattle are consuminghigh-quality forage or supplements thatimprove ruminal digestibility.

B vitamin supplementation. Cattleexperiencing stressful production situationsmay require supplemental B vitamins. Byers(1981) summarized 14 studies that indicatedniacin supplementation helped cattle adjust tothe first 21 to 38 days in the feedlot. With 50to 250 ppm niacin supplementation, growth rateand feed efficiency were improved in mosttrials, averaging 9.7 and 10.9 percent,respectively. Riddell et al. (1981) found agreater response to supplemental niacin in cowsstressed by parturition than for those in mid-lactation. It has been suggested that theimprovement in performance resulting fromsupplemental niacin is related to factorsoccurring in the rumen (Brent and Bartley,1984).

Feeding niacin to ruminally cannulated cattlehas increased bacterial protein production andincreased the molar proportion of propionate(Riddell et al., 1980). Using an in vitro system,Riddell et al. (1980) found a substantialimprovement in microbial protein synthesiswith niacin supplementation (0 to 400 ppm) ofbrome hay and brome:com (1:1) substrates;however, IVDMD was not increasedsignificantly (57 to 58.6 percent for brome hay;71.9 to 72.5 percent for the mixture). Ruminalresponses to supplemental niacin have beenequivocal. Many laboratories (Schussler et al.,1978; Bartely et aL, 1979; Riddell et al., 1980;1981; Shields et al., 1983) have reported

74

improved microbial protein synthesis, whileothers (Schaetzel and Johnson, 1981; Abdouliand Schaefer, 1 986a,b) showed thatsupplemental niacin did not increase productionof microbial protein. These discrepanciessupport the hypothesis of Byers (1981) whosuggested that there is an optimum ruminalniacin concentration, below which microbialprotein synthesis will occur, and above whichthere is no net microbial protein synthesis.

In contrast to the studies reviewed by Byers(1981), supplemental thiamine (Edwin et al.,1976) and the B vitamin complex has notimproved growth performance of weanedcalves (Cole et al., 1979; 1982) or of calvesadjusting to the feedlot (Zinn et al., 1987).Zinn et al. (1987) demonstrated that ruminalsynthesis of most B vitamins is correlatedclosely with feed or energy intake. Theyfurther suggested that responses tosupplemental B-vitamins would be expected foranimals at low intakes, which may offer apartial explanation for the slight reduction inmorbidity in their trial and trials of Cole et al.(1982).

Recent results of Dubeski et al. (1996a)indicated that B vitamin status may becompromised because of decreased synthesisand (or) increased demand. Injecting a vitaminB complex plus vitamin C into calvesrecuperating from 3 days of feed deprivationenhanced the humoral immune response(measured by IgG antibody titers) on day14 and day 28 after infection with bovineherpes virus- 1. Injections were administeredevery 2 day at twice the daily estimated amount(thiamin = 13.5 mg; riboflavin = 33.8 mg;niacin = 135.0 mg; folic acid = 60.0 mg;pantothenic acid = 216.0 mg; vitamin B6 = 108mg; vitamin B12 = 270.0 mg; sodium ascorbate= 1,000.0 mg). In a companion paper, Dubeskiet al. (1996b) demonstrated that plasmaconcentrations of certain vitamins critical to theimmune response in cattle (vitamin B6; vitaminB12; pantothenic acid; ascorbate) weredecreased by the immune challenge. However,ascorbate was the only vitamin of the water-soluble vitamins measured in the calves'

plasma that tended to decrease in concentrationfollowing consumption of prairie grass hay (4percent CP; 1 percent of BW) 20 days afterweaning. The B vitamins measured increasedslightly over the 20-day weaning period. Thisparticular aspect of the results could haveseveral meanings: (1) mobilization of thevitamins from limited body reserves (i.e.vitamin B12 from the liver); (2) the post-weaning feeding regimen was not a sufficientstressor; (3) 20 days after weaning providedample time for the ruminal microorganisms toproduce the B vitamins; or (4) synthesis by theruminal microbes supplied adequate quantitiesof the B vitamins during the 20-day period,even at restricted intake.

Supplementation of the B vitamins appears tobe beneficial only to counteract overt stress anddisease. There is no evidence to indicate thatbeef cattle require vitamin B supplementationunder normal production situations.

Conclusions

As a result of the availability of low costsources of vitamins A and B, regularsupplementation of cattle fed low-qualityforage should be considered. Supplementingother vitamins would not be recommended,except under special circumstances. Theseconditions include supplemental vitamin D forcattle raised in confinement, supplementalvitamin K for cattle consuming foragescontaining dicumarol, and perhapssupplemental B vitamins in overly stressedcattle exposed to disease. The benefit ofadvocating such programs is increasedproduction efficiency. Aside from directeffects on reproduction in the case of vitaminsA and E, producers will benefit from cattle inbetter health.

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Reddy, P.G., J.L. Morrill, R.A. Frey, M.B.Morrill, H.C. Minocha, S.J. Galitzer,and A.D. Dayton. 1985. Effects ofsupplemental vitamin E on theperformance and metabolic profile ofdairy calves. J. Dairy Sci. 68:2,259.

Riddell, D.O., E.E. Bartley, and A.D. Dayton.1980. Effect of nicotinic acid on rumenfermentation in vitro and in vivo. J.Dairy Sci. 63:1,429.

Riddell, D.O., E.E. Bartley, and A.D. Dayton.1981. Effect of nicotinic acid onmicrobial protein synthesis in vitro andon dairy cattle growth and milkproduction. J. Dairy Sci. 64:782.

Rode, L.M., T.A. McAllister, and K.J. Cheng.1990. Microbial degradation of vitaminA in rumen fluid from steers fedconcentrate, hay, or straw diets. Can. J.Anim. Sci. 70:227.

Roquet, J., C.F. Nockels, and A.M. Papas.1992. Cattle blood plasma and redblood cell a-tocopherol levels inresponse to different chemical formsand routes of administration of vitaminB. J. Anim. Sci. 70:2,542.

Ross, D. 1977. Oxidative killing ofmicroorganism by phagocytic cells.Trends Biochem. Sci. 2:61.

Schaetzel, W.P. and D.E. Johnson. 1981.Nicotinic acid and dilution rate effectson in vitro fermentation efficiency. J.Anim. Sci. 53:1,104.

Schubert, J.R., F. Hubbert, Jr., W.A. Sawyer,W.F. Brannon, and J.R. Haag. 1956.The carotene content of stored nativemeadow hay in the northern great basin.Proc. Western Sect. Am. Soc. Anim.Prod. 8:XXXV.

Schussler, S.L., G.C. Fahey, Jr., J.B. Robinson,S.S. Masters, S.C. Loerch, and J.W.Spears. 1978. The effect of nicotinicacid on in vitro cellulose digestion andprotein synthesis. mt. J. Vit. Nutr. Res.48:359.

Shields, D.R., D.M. Schaefer, and T.W. Peny.1983. Influence of niacinsupplementation and nitrogen source onrumen microbial fermentation. J. Anim.Sci. 57:1,576.

Shigemoto, B.S., R.W. Stanley, and S.E.Olbrich. 1980. The effect of seleniumand (or) vitamin E on the incidence ofretained placenta in Hawaii's dairycows. Proc. Western Sect. Am. Soc.Anim. Sci. 3 1:280.

Smith, B.S.W. and H. Wright. 1984. Relativecontributions of diet and sunshine to theoverall vitamin D status of the grazingewe. Vet.Rec. 115:537.

Stabel, J.R., T.A. Reinhardt, M.A. Stevens,M.E. Kehrli, Jr., and B.J. Nonecke.1992. Vitamin E effects on in vitroimmunoglobulin M and interleukin-1 3production and transcription in dairycattle. J. Dairy Sci. 75:2,190.

Sutton, A.L. and J.M. Elliot. 1972. Effect ofratio of roughage to concentrate andlevel of feed intake on ovine ruminalvitamin B12 production. J. Nutr.102: 1,341.

Tengerdy, R.P. 1990. The role of vitamin E inimmune response and diseaseresistance. Ann. New York Acad. Sci.587:24.

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Ullrey, D.E. 1972. Biological availability offat-soluble vitamins: Vitamin A andcarotene. J. Anim. Sci. 35:648.

Van Saun, R.J., T.H. Herdt, and H.D. Stowe.1989. Maternal and fetal seleniumconcentrations and theirinterrelationships in dairy cattle. J.Nutr. 119:1,128.

Wallace, J.D., R.J. Raleigh, and W.P. Skelton.1964. Performance of calves fedvitamin A with baled chopped meadowhay. Proc. Western Sect. Am. Soc.Anim.Sci. 15:XLIX.

Wallis, G.C., C.A. Smith, and R.H. Fishman.1949. The vitamin D content ofroughages. J. Dairy Sci. 32:715.

Washburn, L.E., W.E. Connell, and S.S.Wheeler. 1952. Vitamin A nutrition inreproduction of beef cattle. Proc.Western Sect. Am. Soc. Anim. Prod.3 :XII.

Wasserman, R.H. and A.N. Taylor. 1976.Gastrointestinal absorption of calciumand phosphorus. In: Handbook ofPhysiology, Sect. 7: Endocrinology.Vol. VIII. G.D. Aurbach (ed.).Parathyriod Gland Am. Physiol. Soc.,Washington, DC pp.137-155

Watkins, W.E. and J.H. Knox. 1953. A studyof the supplemental feeding of carotenefor range breeding cows during the pre-calving and calving period. Proc.Western Sect. Am. Soc. Anim. Prod.5 :XI.

Wegner, M.I., A.N. Booth, C.A. Elvehjem, andE.B. Hart. 1940. Rumen synthesis ofthe vitamin B complex. Proc. Soc. Exp.Biol. Med. 45:769.

Wegner, M.I., A.N. Booth, C.A. Elvehjem, andE.B. Hart. 1941. Rumen synthesis ofthe vitamin B complex on naturalrations. Proc. Soc. Exp. Biol. Med.47:90.

Weiss, W.P., D.A. Todhunter, J.S. Hogan, andK.L. Smith. 1 990a. Effect of durationof supplementation of selenium andvitamin E on periparturient dairy cows.J. Dairy Sci. 73:3,187.

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carotene in blood of peripartum cows.J. Dairy Sci. 77:1,422.

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Wheeler, R.R. and W.A. Sawyer. 1956. Theeffect of carotene intake by Herefordcows on calf growth. Proc. WesternSect. Am. Soc. Anim. Prod. 8:XXXVI.

Wheeler, R.R., P.H. Weswig, W.F. Brannon,F.E. Hubert, Jr., and W.A. Sawyer.1957. The carotene and vitamin Acontent of plasma and liver of rangeHereford cows and their calves in theNorthern Great Basin. J. Anim. Sci.16:525.

Wing, J.M. 1969. Effect of source and seasonon apparent digestibility of carotene inforage by cattle. J. Dairy Sci. 52:479.

Zinn, R.Z., KN. Owens, R.L. Stuart, J.R.Dunbar, and B.B. Norman. 1987.B-vitamin supplementation of diets forfeedlot calves. J. Anim. Sci. 65:267.

Zobell, D.R., A.L. Schaefer, P.L. LePage, L.Eddy, G. Briggs, and R. Stanley. 1995.Gestational vitamin E supplementationin beef cows: Effects on calfimmunological competence, growth andmorbidity. Proc. Western Sect. Am.Soc. Anim. Sci. 46:164.

Introduction

Providing nutrients in adequate amounts isimportant for maintaining beef cow fertility. Anutrient is considered essential, if upon removalfrom the diet, there is an interference with ananimal's ability to grow and (or) reproduce.Adequate mineral intake is required for properfunctioning of many metabolic processesincluding reproduction. In general, deficienciesof copper, cobalt, iodine, selenium, zinc,manganese, and phosphorus may occur in cattlemaintained on forage-based diets. The effectsof copper, zinc, manganese, and phosphorus onbeef cattle reproduction are the focus of thispaper.

Trace Minerals

A mineral becomes limiting or deficient whenthe amounts consumed are not adequate to meetdesired performance requirements. In addition,stage of production (pregnancy or lactation)dictates the dietary mineral requirements.Table 1 indicates how copper and zincrequirements vary for growth, pregnancy, andlactation for beef cattle.

TRACE MINERAL SUPPLEMENTATION OF THE BEEF COWAND REPRODUCTIVE PERFORMANCE

Connie K. SwensonZinpro Corp., Eden Prairie, MN 55344

Ray P. AnsoteguiDepartment of Animal & Range Sciences

Montana State University, Bozeman MT 59717

John A. PatersonDepartment of Animal & Range Sciences

Montana State University, Bozeman MT 59717

BretW.HessDepartment of Animal Science,

University of Wyoming, Laramie, WY 82071

83

Mineral deficiencies may be classified either asprimary or secondary (Graham, 1991) with aprimary mineral deficiency caused byinadequate dietary intake of one or moreessential minerals. A secondary deficiency(also referred to as a conditional deficiency) isdue to impaired absorption, distribution, orretention of minerals. A secondary deficiencycan be caused by a preexisting diseasecondition or interaction between minerals,which negatively affects metabolism. Bothprimary and secondary deficiencies can occurat the same time, and evaluating the mineralstatus of cattle can become complex.

Table 1. Copper and zinc requirements for cattle atdifferent stages of productiona.Performance Level Copper Zinc

--mg/kg DM intake--Growth 8-15 26-35Pregnancy 13-20 13-21

Lactation 8-14 8-31

aApted from Graham (1991).

Supplementing trace minerals has been shownto have an impact on reproduction. When zinc,copper, and manganese were added to asupplemental grain mix containing phosphorusand compared to either no supplement, a grain-urea mix, or a grain mix with phosphorus, the

average length of time from the beginning ofbreeding season to conception was 22 days forthe trace mineral supplement, 29 days for thegrain mix with phosphorus, 35 days for thegrain-urea mix, and 42 days fornonsupplemented cows (Doyle et al., 1988).Another study evaluated the effects of anorganic-inorganic trace mineral combinationversus inorganic trace minerals only onreproduction. Conception rates were notinfluenced statistically by type of trace mineralsupplement, but cows which received the tracemineral supplements tended to have higherconception rates, compared to a control with noadded trace elements.

The reasons that intake of bioavailable mineralsis crucial in postpartum animals include properinvolution of the uterus, display of estrus,ovulation, conception, and maintenance of anew fetus Immediately following parturition,the blood supply is shunted from thereproductive organs to mammary glands toenhance milk production. Repair of theendometrium competes with milk productionfor minerals needed for enzyme systems. Thenutritional and mineral status at the cellularlevel is vital to endometrial pathology,embryonic viability, and fertility. In a studyconducted by Manspeaker et al. (1987), copper,zinc, manganese, iron, and magnesium chelateswere added to the basal diet fed to dairyheifers. Following parturition, endometrialtissue involution and regeneration was moreeffective, fewer infections were observed, andincreased ovarian activity and decreasedembryonic mortality were measured insupplemented heifers compared to heifersreceiving no supplemental minerals.

Iodine is also essential for reproductiveperformance. Silent heat, early embryonicdeath, weak calves, retained placenta, anddecreased conception rates have been observedin iodine deficient cows (Corah and Ives,1991). Bull fertility (decreased libido andsperm quality) also can be reduced withinadequate iodine levels. Iodine is providedeasily in salt mixtures, and a deficiency is rarebecause of the common use of iodized salt.

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Copper. Copper is stored in the liver and isnecessary for a variety of enzyme systems.When a copper deficiency occurs, productivitymay be reduced due to metabolic alterations ofenzyme systems. Delayed or suppressed estrusand embryo death (between 30 to 50 days ofgestation) have been identified as commonsymptoms of copper deficiency in beef cattle(Herd, 1994). Copper deficiency in cows canresult in decreased conception, infertility,anestrus, and fetal reabsorption. Dairy cowswith higher serum copper levels hadsignificantly less days to first service, fewerservices per conception, and fewer days fromcalving to conception than cows with lowercopper serum levels. In another study, dairycows with low copper serum levels respondedto supplemental copper and magnesium withincreased percentage of cows that conceived at75, 100, 125, and 150 days after calvingcompared to control, copper supplemented, ormagnesium supplemented only (Ingraham etal., 1987).

Infertility associated with copper deficiencyalso may be caused by an excess ofmolybdenum in the diet. In a study byPhillippo et al. (1987), heifers were fedexperimental diets containing marginal copperlevels and excess molybdenum or excess iron.Heifers receiving the diet with marginal copperlevels and excess molybdenum exhibiteddelayed puberty, lower ovulation rates, andlower conception rates compared to heifersconsuming the diet containing excessive iron.Depressed libido and reduced spermatogenesis,which caused impaired fertility in bulls, hasbeen attributed to excess dietary molybdenum(Thomas and Moss, 1951).

Zinc. Zinc is involved in virtually every phaseof cell growth, and a zinc deficiency can have anegative impact on productivity. Zinc appearsto have more of an impact on male rather thanfemale fertility. Zinc serves as an activator ofenzymes necessary in steroidogenesis, whichregulates secretion of testosterone and relatedhormones. Inadequate zinc levels can causeimpaired spermatozoon maturation and adecrease in circulating testosterone (Apgar,

1985; Puls, 1990). The importance of zinc ingrowing bull calves was demonstrated whenanimals were fed a zinc deficient diet from 8 to21 weeks of age. Reduced testicular size forunsupplemented calves was measuredcompared to calves receiving zinc (PiUs et al.,1966). When zinc then was added to the diet ofthe deficient calves, testicular size equaled thatof the controls by 64 weeks of age. Theseresults suggest that effects of a deficiency canbe overcome by supplementing the deficientmineral. Similarly, Maas (1987) reportedimpaired growth, delayed puberty, anddecreased appetite in zinc deficient bull calves.A loss of appetite results in lowered mineralingestion, which further can decrease feedutilization through hindered nutrientmetabolism.

Zinc deficiency in gestating cows may result inabortion, fetal mummification, lower birthweight, or altered myometrial contractibilitywith prolonged labor. When cows with lowzinc serum levels were supplemented with zincprior to calving, there was a lower incidence ofdystocia (Duffy et al., 1977). Inadequate zinclevels also have been associated with decreasedfertility and abnormal estrus.

Manganese. Manganese is stored in the liver,kidneys, and bones. Manganese is among theleast toxic of all minerals for ruminants becausemature beef animals only absorb 10 to18 percent of dietary inorganic manganese.Manganese absorption drops rapidly with highlevels of dietary calcium, phosphorous, or ironin the diet, which can influence the dietaryrequirement greatly. Fertility was high in cattlefed low levels of dietary manganese and a goodbalance between calcium and phosphorus.However, fertility was depressed if eithercalcium or phosphorus levels became too highand no longer balanced in relation to each other(King, 1971).

Manganese deficiency in cows results in silentestrus, anestrus, infertility, abortion, immatureovaries, and dystocia (Pugh et al., 1985).Corah and Ives (1991) suggested that typicalresponses of females supplemented with

85

manganese include increased ovarian activityand conception rate. The primary mechanismby which manganese has a role in reproductionis through cholesterol synthesis. Manganese isnecessary for synthesis of cholesterol, which inturn is required for ruminant steroidogenesis.Inadequate levels of manganese disruptsteroidogenesis, resulting in decreased levels ofcirculating hormones, abnormal sperm inmales, and irregular estrous cycles in females(Brown and Casillas, 1986).

In addition to signs of reduced reproduction inmature cattle, calves born to deficient damshave general weakness, poor growth, and"knuckle over" at the fetlocks (Dyer and Rojas,1965; Wilson, 1966). Manganesesupplementation is effective in reversingreproductive problems and calf skeletalchanges that are due to a deficiency.

Phosphorus. Of the macro-minerals,phosphorus often has been considered one ofthe most important needed to maintain normalreproductive performance. Forage (the majornutrient source for producing beef cows) has ahigh level of calcium and a low level ofphosphorus, which might lead to theassumption that supplemental phosphorus isnecessary, especially when cattle are grazingmature forage during late fall and through thewinter months. Numerous studies that haveshown a positive impact on reproduction withphosphorus supplementation (Underwood,1966; McDowell, 1985) have been conductedin areas of the world with extreme phosphorusdeficiencies and low fertility in cattle. Resultsmay not be as applicable to the productionsettings in the United States.

Call et al. (1977) conducted a study for 2 yearsusing Hereford heifers fed diets containingeither 66 percent or 172 percent of the NRCrequirement for phosphorus. Reproductionparameters (age at puberty, pregnancy rate, andpercent live calves) were similar betweentreatment groups. In addition, bone sectionsand tissue phosphorus levels were not different.As might be expected, fecal and urine excretionwere much higher for the heifers receiving the

high level of phosphorus. A second studyreported by Butcher et al. (1979) utilizedHereford heifers fed basal diets containing0.14 percent or 0.36 percent phosphorus (66percent or 174 percent NRC requirement) for4 years. During late gestation of the fourthyear, half of the cows in each treatment groupwere reassigned to a very low level ofphosphorus, 0.09 percent, while the other halfof each group remained on their original diets.Supplemental phosphorus levels had nonegative effects on the remaining gestationperiod, calving, or lactation. A decrease inappetite and subsequent weight loss wereobserved in the low level phosphorus group,however. There were no differences in thepercentage of cows bred by natural serviceduring the breeding season. These datasuggested that phosphorus levels below50 percent of NRC recommendations were stilladequate for maintaining fertility.

Forage Mineral Content

Beef producers are faced with the challenge ofbalancing mineral requirements according tothe animal's level of production and mineralcontent available in feed sources. Forages mayprovide all the essential minerals required bycattle, but if the forage is deficient in one ormore minerals, then a mineral supplementwould be necessary to maintain normalmetabolic functions. Severe mineraldeficiencies are uncommon, while marginaldeficiencies are difficult to identify and aremore likely to occur.

Bioavailability of minerals is defined as theproportion of ingested element that is absorbed,transported to the action site, and converted toan active form (O'Dell, 1984).

Distribution of the mineral in the plant,chemical form, and mineral interaction caninfluence bioavailability. Forage mineralcontent and bioavailability varies (Spears,1994). Factors such as soil mineral level, soilpH, climatic conditions, plant species, andstage of plant maturity influence forage mineral

86

content. When comparing legumes and grassesgrown in the same location, legumes have beenshown to be higher in calcium, copper, zinc,and cobalt than grasses. Grasses do, however,contain higher levels of manganese.Concentrations of minerals in forages oftendecrease as plants mature, and dry mattercontent increases more rapidly than mineraluptake.

Mineral analysis of native range grass collectedfrom the same pasture three different yearsduring winter grazing period was similarbetween years for zinc, copper, manganese,iron, potassium, calcium, and phosphorus(Clark et al., 1994). These results suggest thatforage mineral content does not varytremendously from year to year; however, themethod of mineral analysis does not indicatebioavailabilty of the minerals which may beaffected by year-to-year variation in growingconditions.

Deciphering the Feed Tag

Finding mineral requirements for a particulargroup of animals is the easy task. Knowing ifyou have a deficiency and then properlysupplying adequate amounts becomes moredifficult. Diagnosing mineral status of the herdrequires additional information such as animalsymptoms, performance, liver, blood and (or)hair analysis, and feed (possibly water)analysis. Once you have a number of valuesgathered, the bioavailability and interactions ofminerals can be considered in formulating adesired mineral supplement.

However, after you have defined yourdeficiency, is it as simple as formulating asupplement available to your cows? No? Whynot? The first problem is that all minerals arenot created equal in regard to utilization.Secondly, feed tags do not always tell youeverything you need to know and often may beconfusing. Many times, the levels added totrace mineral supplements are given only inorder of incorporation and not in the exactquantities added to the mix. For example, you

may find a trace mineralized salt containingcopper, but the amount of copper is not stated,only that copper oxide is the fourth most usedcompound in a supplement containing 98percent salt. In reality, this supplementcontains very little if any availablesupplemental copper because of the forminwhich the copper occurs.

Even when all the minerals are listedindividually on a feed tag, determining ifmineral requirements are met can be difficultand confusing. It would not be uncommon foryou or have your forage tested at a lab and yourmineral analysis reported back to you as apercent of the forage. When you looked up theanimal requirements, you would find it listed asparts per million (ppm) in the diet, and, upon

ItemAmount fed /dayConversion to kg

Grass Hay22 lb22lbxO.454= 10kg

87

reading the feed tag, you find the amount ofmineral given as milligrams per pound (mg/lb).You are now comparing apples, oranges, andgrapes. Although the conversions to a commondenominator are relatively simple, care must betaken, because being off by one decimal pointmay be the difference between a deficient andtoxic mineral supplement. Table 2 provides anexample of a "miscalculation."

The calculations in Table 2 are correct if thesupplement contained 0.02 percent copper. Inpractice, you should never find a mineralsupplement containing 2 percent copper. Tohelp simplify conversions between unitscommonly used in reference to nutrients, thefollowing table (Table 3) has been provided.

Table 2. Example of a common error in calculating daily intake of copper for cows.

Copper analysis 5 ppm 2%Conversion to mg/kg 5 x 1.0= 5 mg/kg 0.02 / 0.000 1 = 200 mg/kgaDaily intake of copper 10 kg x 5 mg/kg =50mg 0.0567 kg x 200 mg/kg = 11.34 mg 61.34 mgb

aA common error occurs at this point; when converting from percent to ppm, use the whole number,not the decimal equivalent (2% = 2 / 0.000 1 0.02 / 0.000 1).b6134 mg copper / 10.0567 kg feed = 6.1 mg/kg (ppm) copper. This example shows the copperrequirement not being met when actually it would be toxic at 1,134 ppm copper.

Mineral Supplement Total Intake2 ounces2 ounces x 0.02835 = 0.0567 kg 10.0567 kg

Table 3. Conversion factors for commonly used units in reference nutrients.

Unit Conversion Factor UnitMultiply going right*<- Divide going left

lb 0.454 kglb 454.0 gOZ 0.02835 kgoz 28.35 gg 0.001 kgg 1000.0 mgmg/kg 0.454 mg/lbg/kg 0.454 g/lbppm 1.0 mg/kgppm 0.0001 %ppm 0.454 mg/lbppm 0.91 g/tong/ton 0.00011 %

Summary

Maintaining fertility in beef cattle requiresadequate dietary intake and absorption ofessential minerals. The minerals are necessaryfor normal function of various enzyme systems.Feeding a diet deficient in a single mineral canaffect reproduction negatively in beef cows andbulls. The influence of an iodine, copper, zinc,or manganese deficiency on fertility issummarized in Table 4. When evaluating cattlediets for the different stages of production,levels and interactions of minerals should beconsidered. If a deficiency is evident, thensupplementing to meet the animal'srequirement could have a positive impact onreproduction and profitability for the beef cattleproducer.

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Table 4. Summarized influence of iodine, copper, zinc, and manganese deficiency on fertility of beefcattle.

Deficiency Female Fertility Reference Male Fertility Reference

Iodine 11 Silent heat 6 J...L Libido 6

'ft Embryonic death LL Sperm quality

'ft Weak calves

ft Retained placentas

JL Conception rates

Copper 11 Delayed or 11, 12, 13

suppressed estrus

'ir Embryo death

LL. Conception rates

Coppera Delayed puberty 19 Ji. Libido 24

LL Ovulation rates .LL Spermatogenesis

Zinc 'ft Dystocia 8, 15 Impaired growth 1, 15, 20

11 Abnormal estrus Delayed puberty 22

JL Testosterone

.LL. Testicular size

JL Libido

Manganese 'ir Anestrus 2, 6, 21 11' Abnormal sperm 2

11' Abortion

'ft Dystocia

JL Ovarian activity

.LL Conception rates

aCopper with excess molybdenum in the diet.

89

Literature Cited

Apgar, J. 1985. Zinc and reproduction. Ann.Rev. Nutr. 5:43.

Brown, M.A. and E.R. Casillas. 1986.Manganese and manganese-ATPinteractions with bovine spermadenylate cyclase. Arch. Biochem.Biophys. 244:7 19.

Butcher, J.E., J.W. Call, J.T. Blake and J.L.Shupe. 1979. Dietary phosphoruslevels can cause problems in beef cows.Proceedings, West. Sect. Amer. Societyof Anim. Sci. 30:3 12.

Call, J.W., J.E. Butcher, J.T. Blake, J.L. Shupeand R.A. Smart. 1977. Influence ofphosphorus and parainfluenza3 virus onreproduction in beef cattle. Proceedingsof West. Sect. Amer. Society of Anim.Sci. 28:225.

Clark, C.K., V.M. Thomas, and K.J. Soder.1994. Adequacy of winter range foragein meeting dietary mineral requirementsof gestating ewes. Proceedings West.Sect. Amer. Society of Anim. Science.45:219.

Corah, L.R. and S. Ives. 1991. The effects ofessential trace minerals on reproductionin beef cattle. Vet. Clin. of N. Amer.:Food Anim. Prac. 7:41.

Doyle, J.C., J.E. Huston and D.W. Spiller.1988. Influence of phosphorous andtrace mineral supplementation onreproductive performance of beef cattleunder range conditions. J. Anim. Sci.66(Suppl.):462.

Duffy, J.H., J.B. Bingley, and L.Y. Cove.1977. The plasma zinc concentration ofnonpregnant, pregnant, and parturientHereford cattle. Austral. Vet. J. 53:5 19.

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Dyer, l.A. and M.A. Rojas. 1965. Manganeserequirements and functions in cattle. J.Am. Vet. Med. Assoc. 147:139.

Graham, T.W. 1991. Element deficiencies incattle. Vet. Clin. of N. Amer.: FoodAnim. Prac. 7:153.

Herd, D.B. 1994. Identifying copperdeficiencies under field conditions. In:Proc. Florida Ruminant Nutr. Symp.pp. 76.

Ingraham, R.H., L.C. Kappel, E.B. Morgan andA. Srikandakumar. 1987. Correction ofsubnormal fertility with copper andmagnesium supplementation. J. DairySci. 70:167.

King, J.O.L. 1971. Nutrition and fertility indairy cows. Vet. Rec. 89:23 0.

Maas, J. 1987. Relationship between nutritionand reproduction in beef cattle. Vet.Clin. N. Amer.: Food Anim. Prac.3:633.

Manspeaker, J.E., M.G. Robi, G.H. Edwardsand L.W. Douglass. 1987. Chelatedminerals: Their role in bovine fertility.Vet. Med. 82:951.

McDowell, L.R. 1985. Nutrition of grazingruminants in warm climates. AcademicPress Inc., New York.

O'Dell, B.L. 1984. Bioavailability of traceelements. Nutr. Rev. 42:301-308.

Phillippo M., W.R. Humphries, T. Atkinson,G.D. Henderson, and P.H. Garthwaite.198Th. The effect of dietarymolybdenum and iron on copper status,puberty, fertility, and oestrous cycles incattle. J. Agric. Sci., Camb. 109:321-336

PiUs, W.J., W.J. Millers, O.T. Fosgate, J.D.Morton, C.M. Clifton. 1966. Effects ofzinc deficiencies and restricted feedingfrom 2 to 5 months of age onreproduction in Holstein bulls. J. DairySci. 49:995.

Pugh, D.G., R.G. Elmore, and T.R. Hembree.1985. A review of the relationshipbetween mineral nutrition andreproduction in cattle. Boy. Prac.20:10.

Puls, R. 1990. Mineral levels in animal health.Sherpa International. Clearbrook,British Columbia, Canada

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Spears, J.W. 1994. Minerals in forages. In:Forage quality, evaluation, andutilization. G.C. Fahey, Jr. (ed.),American Society of Agronomy, Inc.Madison, WI.

Thomas, J.W. and S. Moss. 1951. The effect oforally administered molybdenum ongrowth, spermatogenesis, and testeshistology in young dairy bulls. J. DairySci. 34:929.

Underwood, E.J. 1966. The mineral nutritionof livestock. The Central Press, Ltd.,Great Britain.

Wilson, T.G. 1966. Bovine functional fertilityin Devon and Cornwall: Response tomanganese therapy. Vet. Rec. 79:562

TRACE MINERAL SUPPLEMENTATION OF THE BEEF COW TO IMPACTIMMUNOLOGIC RESPONSE

Connie K. SwensonZinpro Corp., Eden Prairie, MN 55344

Ray P. AnsoteguiDepartment of Animal & Range Sciences

Montana State University, Bozeman MT 59717

John A. PatersonDepartment of Animal & Range Sciences

Montana State University, Bozeman MT 59717

BretW.HessDepartment of Animal Science,

University of Wyoming, Laramie, WY 82071

Introduction

The role of minerals in beef cattle dietscontinues to be a strong area of interest forproducers, veterinarians, and scientists.Minerals are required for a variety of metabolicfunctions, including the immune system'sresponse to pathogenic challenges.Maintaining the immune response throughproper mineral supplementation may have apositive impact on herd health and, ultimately,profitability of cow-calf operations. However,mineral supplementation strategies quicklybecome complex because of differences inforage mineral bioavailability, interactionsamong minerals which can inhibit mineralabsorption, and difficulty in easily assessingcow mineral status. The effects of copper, zinc,cobalt, and chromium on the immune systemare the primary focus of this paper.

Immune System Background

When an animal is exposed to a foreignsubstance (antigen), the defense mechanism ofthe immune system has three ways to respond:(1) cell-mediated immunity, (2) humoralimmunity, and (3) the phagocytic system.Resistance to a disease challenge is dependentupon the speed and effectiveness of each

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response mechanism. The immune system iscomprised primarily of lymphocytes andphagocytes which are produced from cells inthe bone marrow. Lymphocyte production anddifferentiation is regulated by lymphoid organs,such as the spleen and lymph nodes. VitaminsA and D are important for differentiation oflymphocyte cells into T-lymphocytes and B-cells. Cell-mediated immunity requiresT-lymphocytes, and these cells mature in thethymus and then accumulate in the lymphnodes from where they respond to antigens.The functions of the T-cells include killingvirus-infected cells, helping B-cells buildantibodies, regulating the level of immuneresponse, and stimulating activity of otherimmune cells, such as macrophages. Oneroutine method for evaluating a cell-mediatedresponse is intradermal injection of a foreignsubstance such as phytohemagglutinin (PHA-P,a bean protein) and then measuring the swellingof the skin at specific hours post-injection.

The second type of response is referred to ashumoral immunity. B-cells are processed inintestinal lymphoid tissue and differentiate intoantibody-producing cells. The B-cells migrateto areas other than the thymus, produceantibodies in the presence of an antigen, andhelp form antigen-specific T-cells. Someantigens are T-independent and can stimulate

B-cells directly. The humoral immuneresponse is measured as an antibody titer inblood serum.

In the process of vaccinating animals againstdiseases, an antigen is introduced as either amodified live or killed organism. The B-cellsrespond to the vaccine and build antibodies.The level of antibodies produced is at amaximum level approximately 10 days afterinjection and is referred to as the "primaryresponse." When the vaccine is injected asecond time, there is a much more rapidresponse by B-cells, and higher levels ofantibodies are produced which persist formonths. The response to a booster vaccinationis called the "secondary response."

The maximum response by T-cells and B-cellsmay require days, while the phagocytic systemresponds immediately and utilizes bothneutrophils and macrophages. Neutrophils areresponsible for ingesting pathogens anddegrading them (phagocytosis). Neutrophilsproduce free radicals and oxidants to destroythe membrane of the engulfed pathogen. In theabsence of adequate antioxidants, themembrane of neutrophils may also bedestroyed and reduce the function of theneutrophil. Actions of the macrophage includephagocytosis, processing and presentingantigens to lymphocytes, and releasingsubstances which promote responses of theimmune system.

Nutritional status influences an animal'simmune system and its ability to respond topathogenic challenge. In order for the immunesystem to function properly, energy, protein,vitamins, and minerals must be provided to theanimal in adequate amounts. Nutrientdeficiencies have resulted in depressedimmunocompetence and increasedsusceptibility to infectious disease (Beisel,1982). Energy is required for protein synthesis

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and cell replication. Protein provides aminoacids, which are needed for acute phaseproteins, antibodies, and cytokines. VitaminsA and D are necessary for lymphocytedifferentiation into T-cells and B-cells.Vitamin E serves as an antioxidant to protectcellular membrane polyunsaturated fatty acidsin the process of phagocytosis by neutrophils.Minerals also contribute to the antioxidantenzyme system.

Trace Elements, Role in Immunity

Trace elements that are thought to have animpact on productivity of grazing cattle includecopper, zinc, cobalt, manganese, selenium, andiodine. Deficiencies of these minerals havebeen shown to alter various components of theimmune system (Suttle and Jones, 1989).Specific trace mineral deficiencies which havebeen shown to decrease neutrophil function inruminants include copper, cobalt, selenium, andmolybdenum (Jones and Suttle, 1981; Aziz andKlesius, 1986; MacPherson et al., 1987).Decreased cellular immunity, lowered antibodyresponse, and disrupted growth of T-dependenttissue have resulted from inadequate intake ofzinc (Fletcher et al., 1988). Trace mineralrequirements for beef cattle are given inTable 1.

Subclinical mineral deficiencies in cattle maybe a larger problem than acute mineraldeficiency, because specific clinical symptomsare not evident so as to allow the producer torecognize the deficiency (Figure 1). Animalswith a subclinical status can continue toreproduce or grow but at a reduced rate, theyhave decreased feed efficiency, and theimmune system may be depressed.

Table 1. Trace mineral requirements of beef cattle given as dietary concentration (ppm).

aNational Research Council Beef Cattle RequirementsbAgI.jculi.ural Research CouncilcPuls 1990, Mineral Levels in Animal HealthdCopper:Molybdenum ratio; minimum 3.0, adequate 4.3, ideal 6.0-10.0eRequirement is considered adequate with 0.3 percent calcium also in the diet,however; for each additional 0.1 percent increase in calcium, add 16 ppm zinc.

Figure 1. Effets of Trace Mineral Deficiences onlmmu,e Function in Cows and Calves

Source: Wikse, 1992, TAMV Beef Cattle Short Course

Copper. Copper deficiency has been identifiedas the most common trace mineral deficiencyof cattle in the world (McDowell, 1985).Copper is an essential trace element requiredfor numerous enzyme systems: ironmetabolism, mobilization, and connectivetissue metabolism; integrity of the centralnervous system, and the immune system.Copper functions in the immune systemthrough the following: energy production,neutrophil production and activity, antioxidantenzyme production, development of antibodies,and lymphocyte replication (Nockels, 1994).The importance of copper for maintaining thefunctions of the immune system has beendemonstrated in several studies. Copperdeficiency in cattle can alter the immunesystem and increase an animal's susceptibilityto disease. Viral and bacterial challenges havebeen shown to increase serum ceruloplasminand plasma copper in copper-repleted cattle,indicating a major protective role for copper in

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infectious diseases (Stable et al., 1993). Lowcopper status has resulted in decreased humoraland cell-mediated immunity, as well asdecreased neutrophil bactericidal capability insteers (Jones and Suttle, 1981; Xin et al., 1991).

During gestation, the developing calf isdependent on its dam for supplying copper,manganese, zinc, and selenium. The fetusaccumulates copper in the liver at the expenseof the dam with most of the accumulationoccurring after 180 days of gestation. Lowerthan normal tissue reserves in the fetal calf as aresult of deficiency in the dam can impairdevelopment and growth (Abdebrahman andKincaid, 1993). Deficient copper levels incows have resulted in increased incidence ofscours in their calves (Smart et al., 1986).Occurrence of abomasal ulcers shortly afterbirth and respiratory problems both have beenattributed to inadequate copper levels in calves(Naylor et al., 1989).

Copper deficiency in cattle may be caused bylow levels of copper in forage. Absorption ofcopper is higher for dried forage compared tofresh grasses due to a slower passage ratethrough the gut, allowing for more absorption.Interactions with other dietary mineral sourcesmust be given consideration; particularly, highlevels of molybdenum or sulfur. Molybdenumties up copper, making it unavailable to theanimal, and creates problems when dietarymolybdenum levels are in excess of 1 to 3 ppmor the copper to molybdenum ratio falls below3:1. The interaction of molybdenum andcopper can be intensified with sulfur. Sulfur

Reference Cu Zn Mn Co I Fe Se CrNRCa 1984 8 30 40 0.1 0.5 50 0.2ARCb 1980 12 30 25 0.1 0.5 30 0.1PUlsc 1990 10d 45e 40 0.1 0.5 100 0.3 --

forms thiomolybdates which bind to copper inthe rumen to form insoluble complexes that arepoorly absorbed (Gooneratne et al., 1989;Spears, 1991). In general, 10 ppm copper (drymatter basis) in the diet is considered adequate.Providing 0.2 to 0.5 percent copper in a mineralmix can correct a copper deficiency caused bylow forage copper. However, an excess of0.5 percent may be required if interactions withother minerals decrease copper absorption. It isimportant to assess the copper status of cattlebefore routinely adding excess copper to diets,because ruminants are more sensitive to coppertoxicity than are nonruminants. Copper levelsin the diet exceeding 200 to 800 ppm for cattleand 115 ppm for calves are potentially toxic(Corah, 1993).

Liver biopsy provides the best indication ofcopper status in live cattle. Puls (1990)suggests liver copper levels of 25 to 100 ppm(wet weight basis) are adequate, with 0.5 to10 ppm being deficient and 250 to 800 ppmbeing toxic. Serum copper levels are.not agood indication of copper status. All coppercirculating in the blood is not available to theanimal, and serum copper values can beaffected by a number of factors, includingdietary molybdenum and sulfate, infection,trauma, and stage of gestation (Puls, 1990). Inaddition, serum copper levels do notcorrespond to liver copper, and are notconsidered a reliable indicator of copper statusin cattle (Clark et al., 1993). Cattle with lowplasma copper levels have been found to haveadequate liver copper levels (Muiryan andMason, 1992). If serum copper values areused, a value below 0.6 ppm would indicate apotential deficiency.

Given the complexity of determining copperstatus in cattle because of interactions withother minerals, variability of available copperin forage and bioavailability of copper in theanimal, dependence on a single variable ofcopper status can result in an erroneousdiagnosis. For a more accurate understandingof copper status, correlations must be madebetween copper tissue levels, forage analysis,water analysis, and possibly plasma

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ceruloplasmin activity (Wikse et al., 1992).The most obvious clinical symptom is a changein the appearance of the hair coat. The colormay look faded, and overall hair condition isrough. Other symptoms include generalanemia, abnormal bone and ligamentdevelopment, and a reduction in growth rate.

Zinc. Zinc is involved actively in enzymesystems through metabolism of feedconstituents such as protein and carbohydrateas components of insulin. As in the case ofcopper, zinc is required for maintainingresponsiveness of the immune system. Zincfunctions in the immune system through energyproduction, protein synthesis, stabilization ofmembranes against bacterial endotoxins,antioxidant enzyme production, andmaintenance of lymphocyte replication andantibody production (Nockels, 1994). Zincdeficiency has been shown to have animportant impact on immunity. Calves with agenetic disorder which interferes with zincmetabolism resulting in zinc deficiency exhibitthymus atrophy and impaired lymphocyteresponse to mitogen stimulation (Perryman etal., 1989). A lower percentage of lymphocytesand higher percentage of neutrophils in theblood has been observed in animals consuminga diet deficient in zinc (Droke and Spears,1993).

Zinc has been shown to have a positive impacton immunity in stocker and feedlot cattle withlimited research in beef cows. Weaned calvesnormally experience stress due totransportation, changes in feed, and handling,which increases susceptibility to infectiousdiseases. During this period of stress,providing adequate dietary zinc may be critical,because stress hasbeen shown to have anegative impact on zinc retention Nocke1s etal., 1993). Infection also can have adetrimental effect on zinc status in cattle.Infecting cattle with a bovine rhinotracheitischallenge increased urinary zinc excretion,which caused a negative balance (On et al.,1990). Feed intake often is depressed whenfeeder cattle are stressed, and the reduction inintake results in a decrease of trace minerals

ingested. Supplying zinc to steer calves whichhad undergone stress (weaning, transportation,exposure to new cattle, and vaccination) wasshown to increase feed intake (Spears et al.,1991). Serum zinc levels were lowest duringthe peak morbidity in a natural outbreak ofbovine respiratory disease, and steer calveschallenged with infectious bovinerhinotracheitis virus had a decline in serum zinc(Hutcheson, 1989). It has been suggested thatimmune capacity can be lowered substantiallydue to inadequate dietary levels of zinc beforeany clinical symptoms appear (Fraker, 1983).Zinc supplementation for stressed cattleenhanced recovery rate in infectious bovinerhinotracheitis virus-stressed cattle (Chirase etal., 1991). Zinc methionine also has beenshown to increase antibody titer against bovineherpesvirus-1 (Spears et al., 1991).

Limited research has been done to determinethe effects of zinc supplementation on beefcows. The dietary zinc requirement forgestating beef cows may increase during thelast trimester of pregnancy. Liver and plasmazinc levels have been shown to decrease priorto parturition due to demands for deposition infetal tissue (Xin et al., 1993). Supplementingzinc to dairy cows during lactation resulted infewer infections of mammary glands (Spain etal., 1993). In grazing cows with sucklingcalves, zinc supplementation resulted in a 6percent improvement in weight gain for calveswith no change in cow weight gain (Mayland etal., 1980).

Zinc status of cattle is not easily assessed.Currently, there is not a good indicator fordetermining marginal deficiencies. Levels of25 to 100 ppm (wet basis) in liver and 0.8 to1.4 ppm in serum have been suggested to beadequate (Puls, 1990). Collecting blood forzinc analysis requires a specialized blood tubefor mineral analysis. Analyzing hair for zincalso may be useful for long term monitoring.Clinical signs of zinc deficiency includedparakeratosis, rough hair coat, joint stiffness,and reduced immune response. Feedlot cattlecan have reduced gain but minimal clinicalsigns.

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The recommended dietary level is 30 to 40 ppm(NRC, 1984), and zinc movement in the bodyis regulated precisely within this requirementrange. A level of 80 ppm zinc has beensuggested for stressed and sick feedlot cattledue to decreased feed intake and increasedexcretion (Hutcheson, 1989). Usually availablestores are not available and zinc plasma levelscan decrease rapidly if animals are fed adeficient diet (NRC, 1980). High dietarycalcium decreases the absorption of zinc;therefore, the zinc requirement in the dietincreases. Other minerals (copper, phosphorus,and iron) also can interact and reducebioavailability of zinc. Excess zinc inhibitscopper and iron absorption and utilization.Zinc toxicity is fairly rare in ruminants with themaximum tolerable level reported to be 500ppm (NRC, 1984).

Cobalt. Cobalt functions primarily as acomponent of vitamin B12, which is synthesizedby rumen microorganisms. Cobalt also appearsto have a role in the immune system of cattle.Neutrophils isolated from cobalt deficientcalves had reduced ability to kill a pathogen(MacPherson et al., 1989). Weight gain ofcattle consuming a low cobalt diet wasunaffected until 40 to 60 weeks, but theimmune status (measured as neutrophilfunction) was reduced after 10 weeks (Patersonand MacPherson, 1990).

Cobalt serum levels are not considered to be agood indicator to cobalt status; however, liverlevels reflect status better than serum values.Vitamin B12 concentrations in serum and liverare more reliable indicators of cobalt status.Puls (1990) reports vitamin B12 values whichindicate adequate cobalt levels are between0.25 to 2.50 ppm (wet basis) in liver and 0.40to 0.90 mg/L in serum. If hair samples areanalyzed, a normal value for Co is 0.03 ppm(dry weight). Forage cobalt concentrationsprovide a reliable indicator of cobaltavailability (Spears, 1994), but levels in foragecan be influenced by cobalt level in soil andsoil pH.

Clinical symptoms of cobalt deficiency includeloss of appetite (an early symptom), anemia,loss of condition, weakness, rough hair coat,and reduced conception rates. Animals in adeficient state respond rapidly to dietary cobaltsupplementation. Appetite increases in a week,weight gain follows quickly, but remissionfrom anemia occurs more slowly. Toxicitysymptoms are similar to those for deficiency.Cobalt levels are considered toxic if above 10ppm in the diet.

Chromium. Chromium has been shown to playa role in the immune system. Chromium aidsinsulin function, increases seruminimunoglobulins and retention of other traceminerals, and reduces serum cortisol. Cortisolhas been found to inhibit production andactions of antibodies, lymphocyte function, andleucocyte population (Munck et al., 1984).Chromium supplementation in calves reducedserum cortisol and increased serumimmunoglobulins (Chang and Mowat, 1992).Effectiveness of vaccines may be improvedwith adequate levels of chromium by reducingcortisol levels and their inhibitory effects on theimmune system.

Stressed feeder calves receiving supplementalchromium had improved weight gain andreduced morbidity the first 28 days while on acorn silage diet (Moonsie-Shageer and Mowat,1993) suggesting that chromium may belimiting in corn silage diets. Chromiumsupplementation reduced rectal temperatureand increased blood antibody titers.Implications from this study suggestedinclusion of chromium in preconditioning diets,during marketing and shipping, or in receivingrations may improve performance andimmunocompetence.

Dairy cows fed diets based on grass hay,haylage, and corn silage were supplementedwith chelated chromium (0.5 ppm) 6 weeksprior to parturition and until 16 weeks oflactation or received no supplement. Ahumoral response was measured, andsupplemented cows had an increase in antibodytiter. It appeared that the chromium had a

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significant immunomodulatory effect in cows(Burton et al., 1993).

Investigating the use of chromiumsupplementation is fairly new, and little isknown about the dietary requirement ofruminants. Puls (1990) does not indicate arequired dietary level, but does suggest that achronic dose would be 30 to 40 mg/kg zincchromate for 1 month. Normal serumchromium is given as 0.25 to 0.30 ug/L andliver chromium as 0.04 to 3.8 ppm on a wetbasis. Chromium interactions with otherminerals appears to be positive. It has beensuggested that supplemental chromiumprevents stress-induced losses of copper, zinc,manganese and iron (Schrauzer et al., 1986).

Trace Mineral Sources

Trace minerals for supplements are available indifferent forms: inorganic, chelates, proteinates,and complexes. Chelates, proteinates, andcomplexes often are grouped together and arereferred to as protected minerals. However,there are differences among them. Chelatedminerals are associated with 1 to 3 moles ofamino acids and form a closed ring structure.Proteinated minerals are associated with eitheramino acids or small peptides, which result inan open ring structure. Complexes are mineralsbonded to an organic compound. All forms ofprotected minerals have a neutral electricalcharge, while inorganic minerals possess eitherpositive or negative charges.

The process of chelating minerals to organiccompounds occurs naturally through digestivemetabolic pathways. Positive or negativecharges common to inorganic sources enhancethe possibility of ionic binding to transport orenzymatic proteins. The problem with mineralschelated in this manner is that minerals may bebound to compounds with increased molecularsize and decreased absorption. Protectedminerals have a neutral charge; therefore, theminerals are not bound to large molecules, andbioavailability of the minerals is increased.

The availability of copper oxide, coppersulfate, and organic copper has been comparedin several studies. The source of copper(copper sulfate and copper lysine) did not affectsoluble copper concentrations when using an invitro system to estimate availability. Copperlysine appeared to be equal to copper sulfatewhen growth rate, feed intake, feed efficiency,plasma copper, ceruloplasmin activity, andimmune response of growing steers were usedas indicators of utilization (Ward et al., 1993).Lactating beef cows at a commercial cow-calfoperation deficient in copper had increasedliver copper from either copper proteinate orcopper sulfate supplements when compared toa copper oxide supplement (Clark et al., 1993).These results suggested copper availabilityfrom proteinate or sulfate forms was higherthan the oxide form. Contrary to thesefindings, calves fed copper lysine had 53percent greater apparent copper absorption andincreased retention than calves fed coppersulfate during a repletion period (Nockels et al.,1993). The zinc source also was evaluated inthis study, and no differences between zincmethionine and zinc sulfate were found.

Zinc methionine supplementationenhanced recovery rate of IBR stressed cattlecompared to supplementing zinc, oxide (Chiraseet al., 1991). When cattle were challenged withbovine herpes virus, antibody titer formationfollowing vaccination was enhanced with zincmethionine compared to the basal diet withoutadditional zinc or zinc oxide additions.

Montana State University Research

A study was completed recently at the MontanaState University to determine if the form ofsupplemental trace minerals (complexed versusinorganic) fed during the last trimester ofgestation influenced cellular immunity, bloodcell counts, and serum copper and zincconcentrations of heifers and their calves.Pregnant cross-bred beef heifers were allottedto pasture according to expected calving dateand weight. Treatments compared werecontrol, complexed mineral, and inorganicmineral fed ad libitum in mineral feeders. The

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control heifers received trace mineralized saltonly, while the inorganic treatment heifersreceived a supplement which contained 8,818ppm zinc, 2,472 ppm copper, 4,987 ppmmanganese, and 704 ppm cobalt in theinorganic sulfate form. The complex-treatmentheifers received a supplement with zincmethionine, copper lysine, manganesemethionine, and cobalt glucoheptonateproviding the same level of each mineraldescribed for inorganic supplement. Bloodsamples were collected 30 days following thestart of supplementation to measure serumcopper, zinc, and complete blood cell counts inheifers, and in calves within 24 hours of birth.A skin fold test was conducted to measure acell-mediated immune response on the sameday blood samples were collected.

Phytohemagglutinin (PHA-P) was injectedintradermally at two locations on the neck, andthe swelling response was measured at 0, 6, 12,and 24 hours after injection for cows and 0, 4,8, 12, and 24 h after injection for calves. Asheifers calved, they were removed fromsupplemental mineral-treatment groups andplaced in a common pasture. The heifers werebled a second time 1 week after the last calfwas born to determine blood cell counts. Thetime interval from when heifers were removedfrom mineral treatments until this bloodcollection ranged from 7 to 42 days.

Heifers consuming either complex or inorganicmineral supplements had a greater swellingresponse than did the control-supplementheifers at 6 hours post-injection. Maximumswelling appeared sooner in heifers fed thecomplex mineral supplement (at6 hours) with the inorganic-mineral supplementgroups reaching the maximum response at12 hours (Figure 2).

Swelling response in the calves was notaffected by mineral treatments. These datasuggest that a chemical form of mineralsupplement may influence the initiation of cellmediated response to pathogens.

White blood cell counts (Figures 3 and 4) werehighest for complex-supplemented heifers andtheir calves compared to those supplementedwith inorganic minerals or control. Bothcomplex and inorganic supplemented heifershad higher segmented neutrophils than controls(Figure 5). Other studies have reported aninfluence on blood cells from mineralsupplementation. Blood samples collectedafter removal from the supplement were similarfor all cell counts. Results indicate that mineralsupplementation influenced cell counts;however, changes in cell types were dependenton continued supplementation and not on bodymineral storage. Movement of minerals withinthe body may be regulated within therequirement range. Readily available stores ofzinc are quite small, as indicated by drops inplasma zinc values to the deficiency rangewithin 24 hours after switching animals to dietsvery low in zinc (NRC, 1980).

Serum copper and zinc levels for both heifersand calves are given in Table 2. Serum copperconcentrations for the calves were increased byproviding cows added mineralsupplementation; however, the levels measuredare below those considered adequate(0.6 mg/L). Previous studies have shown thatfetal calves accumulate copper in the liver andare born with lower serum copper than adults(Puls, 1990; Abdebrahman and Kincaid, 1993).During the first 3 days postpartum, liver copperdecreases and serum copper levels increase asliver copper is converted to the copperdependent enzymes. Serum zinc was similaramong supplement treatments, and levels ofzinc were in the normal range of 0.80 to 1.00mgIL (Puls, 1990).

Serum copper and zinc values in the heiferswere not influenced by supplementation. Thevalidity of utilizing blood serum as anindication of mineral status in the heifers maybe questionable. Supplemented heifers wereconsuming levels of copper (24 ppm) and zinc(88 ppm) which were twice NRC (1984)requirements; however, heifer serum minerallevels indicate marginal copper deficiency andadequate zinc according to values reported by

99

EE

Puts (1990). Liver samples may have been amore accurate indicator of mineral status in theheifers.

Supplementing 2-year-old heifers in lategestation with zinc, copper, manganese, andcobalt influenced cell-mediated immunity inheifers and blood cell counts in heifers andtheir calves. Heifers receiving complexedminerals had the highest response to cell-mediated immunity and number of white bloodcell and neutrophils, while heifers receivinginorganic minerals had intermediate responses.Future research will continue to investigate theinfluence of trace mineral supplementation onbeef production with emphasis on cow-calfoperations.

Summary

Minerals can have a substantial influence onherd health, production, and profits for theproducer. The importance of minerals dictatesthe need for continued research in severaldifferent areas, such as evaluating the mineralsource to determine levels required in order tomaintain immunity responses, methods toassess animal mineral status more easily, anddetermining optimum levels of specificminerals according to animal performancegoals. The following question needs to beaddressed: Is it possible to develop optimummineral feeding strategies which maximizeproduction and minimize financial cost to theproducer?

Figure 2. Effects of Mneral Supplementaton onHeifer Skinfold Thickness 6, 12, md 24 hours PostInjection with PHA-P

Control - - - Complex Inorganic3

2.52

1.5

0.50

Oh

,/ - --- - ---./ .,, -.

6h 12 h 24 h

E

Figure 3. Influenc of Cow Mineral Supplemenlationon Calf White Blood Cell Count

b

x 10 nm3

Control

a

a

a,b

a,b

11.45

Complex

Fijre 4. Influence of MneralSupplerrentatiai on HeirWhi BloodCell bunls

ntoI0 comØex

Irorgaric

Figi.re 5. Influonce of MireralSupplen-entalion on Heir NeutrophilCounts

x 10mrrlntOI

o ccrrplexhoanc

a,b

Inorganb

Iii ring After

Du,g After

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Table 2. Influence of mineral supplementation on copper and zinc serum levels in heifers and their calves.

aComplex supplement contained the following organic mineral complexes: zinc methiomne (8,818 ppm zn),copper lysine (2,472 ppm cu), cobalt glucoheptonate (704 ppm co) and manganese methionine (4,987 ppm mn).bInorgamc supplement contained zinc, copper, cobalt, and manganese in the sulfate forms and provided

minerals at the same level as the complex supplement.cdMeafl in the same row with different superscripts are different (P < 0.07).

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Chirase, N.K., D.P. Hutcheson and G.B.Thompson. 1991. Feed intake, rectaltemperature, and serum mineralconcentrations of feedlot cattle fed zincoxide or zinc methionine andchallenged with infectious bovinerhinotracheitis virus. J. Anim. Sci.69:4,137.

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Item Complexa Inorganic" Control

Serum copper levels, mg/LHeifers 0.60 0.61 0.63Calves 0.34c Ø33C 031d

Serum zinc levels, mg/LHeifers 0.73 0.70 0.68Calves 1.23 0.88 1.00

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Spain, J.N., D. Hardin, B. Steevens, and J.Thorne. 1993. Effect of organic zincsupplementation on milk somatic cellcount and incidence of mammary glandinfections of lactating dairy cows. J.Dairy Sci. 76 (Suppl):265(Abstr.).

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Spears, J.W. 1991. Advances in mineralnutrition in grazing ruminants. In:Proceedings of the Grazing LivestockNutrition Conf. Steamboat Springs, CO.p. 138.

Spears, J.W., R.W. Harvey, and T.T. Brown.1991. Effects of zinc methionine andzinc oxide on performance, bloodcharacteristics, and antibody titerresponse to viral vaccination in stressedfeeder calves. J. Amer. Vet. Med.Assoc. 199:12:1731

Spears, J.W. 1994. Minerals in forages. In:Forage quality, evaluation andutilization. G.C. Fahey, Jr. (ed.),American Society of Agronomy, Inc.Madison, WI. p. 281.

Stable, J.R., J.W. Spears, T.T. Brown, Jr.1993. Effect of copper deficiency ontissue, blood characteristics, andimmune function of calves challengedwith infectious bovine rhinotracheitisvirus and Pasteurella hemolytica. J.Anim. Sci. 71:1,247.

Suttle, N.F. and D.G. Jones. 1989. Recentdevelopments in trace elementmetabolism and functions: Traceelements, disease resistance andimmune responsiveness in ruminants.Nutr. 119:1,055-1,061.

Ward, J.D., J.W. Spears, and E.B. Kegley.1993. Effect of copper level and source(copper lysine versus copper sulfate) oncopper status, performance and immuneresponse in growing steers fed dietswith or without supplementalmolybdenum and sulfer. J. Anim Sci.71:2,748-2,755.

Wikse, S.E., D. Herd, R. Field, and P. Holland.1992. Diagnosis of copper deficiencyin cattle. J. Amer. Vet. Med. Assoc.200:11:1,625.

Wikse, S.E. 1992. Proceedings 1992 TexasBeef Cattle Short Course.

Xin, Z , D.F. Waterman, R.W. Hemken andR.J. Harmon. 1993. Copper status andrequirement during the dry period andearly lactation in multiparous Holsteincows. J. Dairy Sci. 76:2,711.

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Xin, Z., D.F. Waterman, R.W. Hemken andR.J. Harmon. 1991. Effects of copperstatus on neutrophil function,superoxide dismutase, and copperdistribution in steers. J. Dairy Sci.74:3,078.

4

I

Chapter 4. Supplementation Strategies

Introduction

Livestock production systems are dynamic butmust reach a long-term equilibrium in order tobe biologically and economically sustainable.The system is biologically sustainable if thenumber of grazing animals is in a long-termbalance with the amount of forage produced.The balanced system may be highly productiveif the grazing animals have high geneticpotential and if their requirements are met to ahigh degree. Alternatively, the system may bebalanced yet much less productive if therequirements (and potential) of the animals arelower and (or) nutrients are available from thevegetation at a lower level or in a less favorablepattern. In the latter case, the productionsystem may be biologically but noteconomically sustainable.

Grazing animals develop a behavioral patternin seeking and consuming forages that satisfysome proportion of their physiological needsfor nutrients (Stuth, 1991). Some of theseactivities are instinctive and some may belearned, but a settled-on pattern of behaviorbecomes characteristic of the animals withinthe bounds set by the local circumstances.Depending on the size and topography of thearea, grazing animals may graze the entire areaif small, may graze a small portion (e.g., valleysite) of a large but totally accessible area, ormay travel the entire area with intermittentstops to graze small preferred patches.Supplementation can be an enhancement tobehavioral strategies by increasing theefficiency with which the grazing animalsharvest forage and extract nutrients from it.Conversely, supplementation can be intrusive ifa sustainable strategy is disrupted by anegatively impacting behavioral change.

SUPPLEMENTATION STRATEGIES

James Ed HustonTexas Agricultural Experiment Station

Texas A&M University, San Angelo, TX 76901

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The productivity of the unsupplementedgrazing animal is determined, therefore, by itspotential to produce and how well its nutrientrequirements are satisfied by quantity, quality,and consistency of the grazed forage.Supplementing nutrients to grazing cattle is anadjustment for increasing the efficiency oftransfer of forage nutrients to consumableproducts (meat, milk, and fiber). Once theproper species, classes, and numbers of animalsare selected, practical questions of methods andtiming are appropriate. Adoptingsupplementation does not diminish the need tomaintain balance between the supply of anddemand for forage; but, supplementing canincrease harvest efficiency (i.e., forage intake;Huston et al., 1993) and the nutritional value ofthe forage (i.e., digestibility; DelCurto et al.,1 990a,b), and release the production system tocapitalize from more efficient animals havinghigher requirements (Holloway et al., 1975).Often, the final answers to a supplementationstrategy may be weighted more by economicthan by biological constraints, and it iscommon that the optimal management practicesupports less than maximal productivity. Themost frequently asked questions regardingsupplemental feeding are what and how muchshould be fed. Also important is what methodshould be used in feeding. In this discussion onsupplementation strategies, feeding frequencyand hand- vs. self-feeding are considered. Bothhave biological and economic impact on thesuccess of the practice.

Frequency of feeding

Physiological activities of the ruminant,including those within its gastrointestinalsystem, do not proceed at a constant rate(Swain et al., 1996). Rather, almost allprocesses are cyclical and vary in activity

within the 24-hour day (Beever and Siddons,1984). For example, cattle generally grazeuntil the reticulorumen is full of freshly grazed,poorly chewed forage, then lie down andruminate. A mouthful of forage and liquid areregurgitated, chewed, and then swallowed.This process reoccurs many times until most ofthe material that was originally swallowed, butnot chewed, has been further processed andmade more accessible for attack by rumenmicroorganisms and their digestive enzymes.Fermentation rises along with the release ofammonia and the production of end products offermentation (short-chain fatty acids), therebyincreasing the absorption of these metabolitesthrough the rumen wall and into thebloodstream. The ruminal contents decrease inmass as fermentation occurs. Undigestedparticles are carried along with the liquid phasethat contains ruminally synthesized products asboth exit the rumen to the lower tract wherethey are further processed. At some point, theanimal rises to defecate, drink water, and (or)resume grazing to begin the cycle again.

The number of times that these activities occurwithin the day depends on many factors thatinclude forage availability (that influencesharvest rate), forage quality (that influencestotal intake, ruminating duration, and passagerate), and environmental factors (such as daylength, temperature, wind speed, precipitation,etc.). Some cycles occur many times within a24-hour period (eating cycles with rises andfalls in rumen ammonia and blood urea levels),some approximately at 24-hour intervals(common watering interval), and some lessfrequently (hormonal cycles, including thoseassociated with the estrus cycle).

Supplemental feeding affects the normalcycles, and, depending on the composition ofthe supplemental feed, different changes occur(Doyle, 1987). High grain (starchy) feedscontain a relatively small amount of protein(less than 15 percent) but are highly and rapidlyfermented by the rumen microorganisms.Rumen microorganisms in grazing animals,especially when forage quality is low, areadapted to fermentation of fiber (cellulose), a

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rather slow process. If grain is introduced intothe rumen, fermentation increases and short-chained fatty acids are produced at anaccelerated rate, thereby increasing the acidityof the rumen environment (drop in pH level).If this dietary change is abrupt and a substantialamount of grain is fed, the animal is in dangerof acute lactic acidosis, which puts the animalin physiological crisis and may cause death. Ifthe grain is introduced gradually and fedfrequently, the rumen microbial population willadapt and capitalize on the more accessiblenutrients (high energy and adequate protein).Although the fiber may be less well digested(Russell and Wilson, 1996), the increased valueof the grain can more than offset a smalldecrease in fiber digestion and possibly inforage consumption. In some instances, low-level grain feeding stimulates fiber digestion bycreating more microbial activity and either doesnot affect or slightly increases forageconsumption (Doyle, 1987; Obara et al., 1991).This usually occurs when the rumenenvironment is maintained at a somewhatsteady state (daily dietary ingredients areproportionally similar).

Feeding of a high protein supplement does notresult in an abrupt increase in volatile fatty acidproduction but increases ruminal ammonia andstimulates the microbial population to fermentfiber. If the forage in the diet is low quality(low in digestibility and protein), then theanimal will benefit from protein feeding in fourimportant ways. The protein in the supplementis broken down partially in the rumen. Theproducts that include peptides, amino acids,ammonia, and various carbon fragmentsbecome part of the ruminal metabolic pool,yield some energy, and stimulate fermentationof dietary fiber. Benefits include: (1) acontribution to the digestible energy (fermentedfragments), (2) increased fiber digestion andenergy yield from fiber, (3) increased flow ofprotein (from diet and from rumen synthesis) tothe lower tract for digestion, and (4) increasedforage consumption because of decreasedruminal fill. Intermittent feeding of starch(high grain supplements) results in constantadjustments in the rumen population.

Intermittent feeding of a protein concentrate,which is usually lower in starch and higher infiber, is relatively non-intrusive to the dynamicequilibrium of the rumen population.

The dynamics of the relationship between theruminal microbial population and the hostanimal suggest that steady state nutrition is notessential for normal metabolic processes tocontinue. Hunt et al. (1989) showed thatfeeding of cottonseed meal at 12-, 24-, and 48-hour intervals to steers equally increased theparticulate passage rate and intake of low-quality grass hay. An earlier study by Mcllvainand Shoop (1962) showed that weaner steersgrew approximately as well grazing onrangeland during a winter feeding period andsubsequent summer period whether they werefed daily equivalents of 1 to 1.5 lb ofcottonseed cake daily, every third day, orweekly. Similar results have been reported atother locations with other classes of cattleeither grazed or fed low-quality forages(Collins and Pritchard, 1992; Huston et al.,1986, 1996, 1997; Melton and Riggs, 1964;Wettemann and Lusby, 1994).

However, conflicting results have occurredwhen high-grain supplements were fed atdifferent intervals. Chase and Hibberd (1985a)found that alternate-day feeding of high-grainsupplements reduced intake of native grass hay(crude protein (CP) = 5 percent) compared todaily feeding of the same supplements.Moreover, a separate study by these sameresearchers (Chase and Hibberd, 1 985b)showed that feeding corn at levels above2 lb/day to adult cows decreased both intakeand digestibility of native grass hay (CP = 4.2percent). Similar results were reported byAdams (1986). Presumably, these reductionswere the result of lowered pH in the rumen,thereby decreasing the activity of fiber-digesting microorganisms. On the other hand,Beaty et al. (1994) fed cows supplements ofincreasing protein (decreasing grain) contentand found daily feeding only slightly moreeffective than less frequent feeding (three timesper week) with no interaction for frequency Xcomposition. Huston et al. (1996) found that

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feeding a cottonseed meal:sorghum grainmixture (30:70) was of no value for cowsgrazing dormant Texas rangeland when fed at alow level either three times per week orweekly. However, when the mixture was fed ata high level (to provide equal protein with 2.1lb/head/day cottonseed meal alone), it was aseffective as the cottonseed meal even when fedin a once/week feeding of up to 30 lb/cow.This was a surprising result and requiresadditional study. Perhaps at the low feedinglevel, the expected decline in forage intake andfiber digestion occurred, thereby negating anybenefit. At the higher feeding level(approximately 4.25 lb/day), the amount ofenergy and protein supplied may have offsetany disadvantage due to substitution. Thequestion of why those cattle fed a very highlevel of grain once per week were not adverselyaffected with grain overload (lactic acidosis) isopen to question.

It is likely that the effectiveness of infrequentfeeding of protein supplements is dependent onthe demonstrated capacity of the ruminant fornitrogen recycling (Houpt and Houpt, 1968;Hume et al., 1970). A high protein supplementfed every 3 to 7 days results in a large increasein rumen ammonia within a few hours afterfeeding (Beaty et al., 1994) followed by a risein blood urea concentrations. In cows fedsupplements once per week, at least onesubsequent peak in blood urea occurs on aboutday 4 (Huston, unpublished data). Thispresumably is associated with recycling ofabsorbed nitrogen back to the rumen, where itagain stimulates fiber digestion, proteinsynthesis, and forage intake before beingreabsorbed in various forms and convertedpartially to urea once again. It seems clear thatinfrequent feeding, although not alwaysbiologically optimal, is an acceptable and safepractice; but, at the present, it should notextend to high-grain supplements or thosecontaining readily hydrolyzable nonproteinnitrogen.

Timing of supplementation

Supplemental feeding should be planned tomaximize the value of the nutrients suppliedand minimize the negative effects on animalbehavior. Robinson (1996) suggested thatfeeding cows a protein supplement 1 hourbefore feeding a mixed ration provided rumen-soluble nitrogen at a low point of rumenammonia and stimulated microbial growth priorto the ingestion of the mixed ration. The resultwas a rise in milk production. Night feeding ofdairy cows increased fermentation rate withoutchanging animal performance (Nia et al., 1995)and increased digestibility of the rest of the dietwhile concurrently decreasing the ruminalescape of dietary protein (Robinson, 1997).Clearly, these findings are interesting but notapplicable to most range livestock settings.

Adams (1986) showed that steers fed a cornsupplement in the early afternoon (duringresting time) gained more weight than those fedduring the morning grazing period. Additionalwork is needed in this area to clarify theinterrelationships between time ofsupplementation, ingestion of forage, andgrazing behavior.

Hand-feeding vs. self-feeding

Critical to the success of supplemental feedingis selecting a method that will deliver thedesired amount of feed to the herd withminimal variability among the individual cows.Bowman and Sowell (1997) examinedavailable information and concluded thatoptimal trough space and supplementallowances were important for hand-feeding.Inadequate space excluded some individualsfrom consuming supplement, and excess spaceincreased the impact of dominant cows.Approximately 1 m per cow is adequate troughspace for hand-feeding. Better distributionamong the individuals in the herd accompaniedhigher feed allocations. Although self-feedingtended to reduce the percentage of cows thatdid not consume supplement, the disparity(coefficient of variation) in amount consumed

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among individuals could be just as large orlarger as when cows were hand-fed. Otherfactors that affected average consumption andwithin herd variability included supplementform (liquid, block, tub, etc.), formulation(block hardness, urea vs. preformed proteincontent, nutrient levels, etc.), and animalfactors (e.g., social interactions).

In studies with ewes (Weir and Torell, 1953)and cows (Riggs et al., 1953), self-feeding of acottonseed meal and salt mixture was shown tohave similar effects on animal performancewith hand-feeding cottonseed meal at therecommended level. Salt levels of 25 to 35percent of the mixture were considerednecessary to limit intake to desired levels. In astudy in Venezuela with crossbred steersgrazing Pangola pastures, Chicco et al. (1971)found a mixed ingredient supplement (57percent polished rice, 40 percent sesame meal,and 2.8 percent bone meal; CP = about 23percent) increased gains similarly whether self-limited by an addition of 30 percent salt orhand-fed without salt (46 percent and 57percent, respectively). Brandyberry et al.(1991) found that approximately 20 and 30percent salt in mixtures would limit intake of asupplement by steers to 1 kg per head per dayduring summer and winter, respectively. Theyfound very similar grazing behavior in steersthat were either self-fed or hand-fed daily invery small (4 ha) pastures. Whether thesesimilar behavior patterns would be displayed inextensive pastures was not tested.

Clearly, the question of feeding method (hand-feeding vs. self-feeding) involves both feedingfrequency and timing and their effects ongrazing behavior. In small pastures orpaddocks, feeding method would not be asimportant as in extensive situations. In smallenclosures, time and distance do not restrictanimal grazing opportunity. Whether cowsvisit a feeding location once a day, severaltimes per day, or once every few days will nothave a major influence on their opportunity tograze the entire area. On the other hand, cowson an extensive area may shorten their grazingtime if they visit a feeding location frequently.

In a study with sheep (Hatfield et al., 1990),supplemented ewes fed daily loafed more thanthose that were unsupplemented, and as aresult, grazed less and tended to weigh lessafter the winter feeding period. This illustratesthe possibility that feeding a small amount toanimals that are marginally undernourishedbecause of extensive, low availability of foragemay be detrimental rather than beneficial ifgrazing behavior is disrupted. Self-feedingwould reduce the "anticipation factor" andencourage the animal to continue grazinglonger. Self-fed animals have continuousaccess to the supplement (less "bully" effect),except occasionally when the dominantindividual "stands guard" at the trough. Hand-feeding daily allows aggressive individuals toconsume disproportionately greater amountscompared with those that are more submissive.The alternative of hand-feeding greateramounts at less frequent intervals is lessdisruptive and reduces the variation inconsumption, presumably because dominantcows are less aggressive during the feedingevent (Huston et al., 1997).

Conclusion

It is suggested that the most appropriate feedingmethod may be different for various productionsystems. If practical, frequent feeding to attainsteady state conditions is most desirable (Beatyet al., 1994). If all else is equal, hand-feedingand self-feeding in small pastures give similarresults. Therefore, the method of choice shouldbe determined by economics and value ofconvenience. In extensive pastures, theadditional considerations of animal behaviorand grazing distribution are important. It issuggested that daily hand-feeding is the leastdesirable method for extensive systems. Somefeed types (e.g., liquid feeds containing NPN asa major crude protein source) that should becontinuously accessible must be self-fed. Otherfeeds, such as high-protein meals and cubes,can be fed infrequently for immediateconsumption by the herd. Some feeds, such asself-limiting meals, blocks, and tubs, can beself-fed or fed infrequently for consumption

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during a portion of the feeding interval. Majorconsideration should be given to the effects ofthe supplement on the animals, grazingbehavior and on the value of the consumableforage. The most palatable supplement may bethe least valuable choice.

Literature Cited

Adams, D. 1986. Getting the most out of grainsupplements. Rangelands. 8:27-28.

Beaty, J.L., R.C. Cochran, B.A. Lintzenich,E.S. Vanzant, J.L. Morrill, R.T. Brandt,Jr., and D.E. Johnson. 1994. Effect offrequency of supplementation andprotein concentration in supplements onperformance and digestioncharacteristics of beef cattle consuminglow-quality forages. J. Anim. Sci.72:2,475-2,486.

Beever D.E. and R.C. Siddons. 1986.Digestion and metabolism in thegrazing ruminant. In: Control ofDigestion and Metabolism. L.P.Milligan, W.L. Grovum, and A. Dobson(eds.). Reston Books, Prentice-Hall,Englewood Cliffs, NJ. pp. 479-497.

Bowman, J.G.P. and B.F. Sowell. 1997.Delivery method and supplementconsumption by grazing ruments: Areview. J. Anim. Sci. 75:543-550

Brandybeny, S.D., R.C. Cochran, E.S.Vanzant, T. DelCurto, and L.R. Corah.1991. Influence of supplementationmethod on forage use and grazingbehavior by beef cattle grazingbluestem range. J. Anim. Sci. 69:4,128-4,136.

Chase, Jr. C.C. and C.A. Hibberd. 1985a.Feeding frequency of high grainsupplements with low quality nativegrass hay. Oklahoma Agric. Exp. Sta.Misc. Rep. MP-1 17, pp. 211-214.

Chase, C.C., Jr. and C.A. Hibberd. 1985b.Intake and digestibility of low qualitynative grass hay by beef cows fedincreasing quantities of corn grain.Oklahoma Agric. Exp. Sta. Misc. Rep.MP-117, pp.207-210.

Chicco, C.F., T.A. Shultz, J. Rios, D. Plasse,and M. Burguera. 1971. Self-feedingsalt-supplement to grazing steers undertropical conditions. J. Anim. Sci.33:142

Collins, R.M. and R.H. Pritchard. 1992.Alternate day supplementation of cornstalk diets with soybean meal or corngluten meal fed to ruminants. J. Anim.Sci. 70:3,899-3,908.

DelCurto, T., R.C. Cochran, L.R. Corah, A.A.Beharka, E.S. Vanzant, and D.E.Johnson. 1 990a. Supplementation ofdormant tallgras s-prairie forage: II.Performance and forage utilizationcharacteristics in grazing beef cattlereceiving supplements of differentprotein concentrations. J. Anim. Sci.68:532-542.

DelCurto, T., R.C. Cochran, D.L. Harmon,A.A. Beharka, K.A. Jacques, G. Towne,and E.S. Vanzant. 1990b.Supplementation of dormant taligrass-prairie forage: I. Influence of varyingsupplemental protein and (or) energylevels on forage utilizationcharacteristics of beef steers inconfinement. J. Anim. Sci. 68:515-531.

Doyle, P.T. 1987. Supplements other thanforages. In: The Nutrition ofHerbivores. J.B. Hacker and J.H.Temouth (eds.). Academic Press, NewYork. p. 429.

Hatfield, P.G., G.B. Donart, T.T. Ross, andM.L. Galyean. 1990. Sheep grazingbehavior as affected bysupplementation. J. Range Manage.43:387.

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Holloway, J.W., D.F. Stephens, J.V. Whitemen,and R. Totusek. 1975. Efficiency ofproduction of 2- and 3-year-oldHereford, Hereford X Holstein andHolstein cows. J. Anim. Sci. 41:855-867.

Houpt, T.R. and K.A. Houpt. 1968. Transferof urea nitrogen across the rumen wall.Amer. J. Physiol. 214:1,296.

Hume, I.D., R.J. Moir, and M. Somers. 1970.Synthesis of microbial protein in therumen: I. Influence of the level ofnitrogen intake. Aust. J. Agric. Res.21:283.

Hunt, C.W., J.F. Parkinson, R.A. Roeder, andD.G. Falk 1989. The delivery ofcottonseed meal at three different timeintervals to steers fed low-quality grasshay: effects on digestion andperformance. J. Anim Sci. 67:1,360-1,366.

Huston, J.E., K.W. Bales, R.K. Dusek, P.V.Thompson, and D.W. Spiller. 1996.Winter losses in body weight andcondition score of range cows fedsupplements at different intervals. BeefCattle Research in Texas, 1995.pp. 79-82.

Huston, J.E., F.M. Byers, D. Cooper, and L.M.Schake. 1986. Feeding frequency andvariation in supplement and forageintake in cows grazing dormant nativerangeland. Tex. Agric. Exp. Sta. Prog.Rep. PR-4,477.

Huston, J.E., H. Lippke, T.D.A. Forbes, J.W.Holloway, R.V. Machen, B.G.Warrington, K. Bales, S. Engdahl, C.Hensarling, P. Thompson, and D.Spiller. 1997. Effects of frequency ofsupplementation of adult cows inwestern Texas. Proc. West. Sect. Amer.Soc. Anim. Sci. 48:236-238.

Huston, J.E., P.V. Thompson, and C.A. Taylor,Jr. 1993. Combined effects of stockingrate and supplemental feeding level onadult beef cows grazing nativerangeland in Texas. J. Anim. Sci.71:3,458-3,465.

Mcllvain, E.H. and M.C. Shoop. 1962. Dailyversus every-third-thy versus weeklyfeeding of cottonseed cake to beefsteers on winter range. J. RangeManage. 15:143-146.

Mellon, A.A., and J.K. Riggs. 1964.Frequency of feeding proteinsupplement to range cattle. Tex. Agric.Exp. Sta. Bul. B-1025.

Nia, S., P.H. Robinson, M. Gill, J.R. Ingalls,and J.J. Ketmelly. 1995. Influence offeeding a rapidly rumen degradeddietary protein at night or with a basalmixed ration on performance of dairycows. Can. J. Anim. Sci. 75:575-582.

Obara, Y., D.W. Dellow, and J.V. Nolan.1991. The influence of energy-richsupplements on nitrogen kinetics inruminants. In: Physiological Aspects ofDigestion and Metabolism inRuminants. T. Tsuda, Y. Sasaki, and R.Kawashima (eds.). Academic Press,Inc., New York. p.515.

Riggs, J.K., R.W. Colby, and L.V. Sells. 1953.The effect of self-feeding salt-cottonseed meal mixtures to beef cows.J. Anim. Sci. 12:379-393.

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Robinson, P.H. 1996. Strategies of feedingsupplemental soybean meal toprimiparous dairy cows. Can. J. Anim.Sci. 76:105-112.

Robinson, P.H. 1997 Influence of time offeeding a protein meal on ruminalfermentation and fore stomach digestionin dairy cows. J. Dairy Sci. 80:1,366-1,373.

Russell, J.B. and D.B. Wilson. 1996. Why areruminal cellulolytic bacteria unable todigest cellulose at low ph? J. Dairy Sci.79: 1,503-1,509.

Stuth, J.W. 1991. Foraging behavior. In:Grazing Managementz; An EcologicalPerspective. R.K. Heitschmidt and J.W.Stuth (eds.). Timber Press, Portland,OR. p. 65.

Swain, R.A., J.V. Nolan, and A.V. Klieve.1996. Natural variability and diurnalfluctuations within the bacteriophagepopulation of the rumen. App!.Environ. Microbiol. 62:994-997.

Weir, W.C. and D.T. Torell. 1953. Salt-cottonseed meal mixture as asupplement for breeding ewes on therange. J. Anim. Sci. 12:353-358.

Wettemarm, R.P. and K.S. Lusby. 1994.Influence of interval of feeding proteinsupplement to spring calving beef cowson body weight and body conditionscore during the winter. Okla. Agric.Exp. Sta. Misc. Pub. MP-939, pp. 123-125.

Chapter 5. Dynamics of Supplementing GrazingAnimals

Introduction

This paper intends to discuss sources ofuncertainty in the grazing animal's nutritionalenvironment. In like manner, the intent is todiscuss sources of uncertainty in animal responseto that environment during components of theannual cycle. Managerial response touncertainty is a matter of ecological health of theresource, animal well-being, and economics. Astrategic method the manager can use to respondto such a complex environment is suggested.

The period of time when rangeland forage meetsor exceeds the requirements of producinganimals can be very short to year long. Allrangeland vegetation exhibits periods of non-growth, because of low temperatures or no water.Three arenas of uncertainty characterizevariation in the animal's grazing environment.

Plant

The nutritional content of plants varies in timeand space. Nutrient content varies among plantkinds and parts and among plants of the samespecies. Nutrient content varies because ofdifferences in phylogeny, phenology, themicrosite, and associated plants.

Animal

On the same forage resource, animals may selectvery different diets with very different nitrogenand dry matter digestion (DMD) content.Variation in total ingestion and utilization ofnutrients by individuals is large, includingresponse to under- and over-nutrition. Variationin requirements of individuals is large, because

SUPPLEMENTATION IN AN UNCERTAIN ENVIRONMENT:DYNAMICS OF THE GRAZING RESOURCE

Larry R. RittenhouseRangeland Ecosystem Science Department

Colorado State University, Fort Collins, CO 80523

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of differences in demographics related to age,sex, and physiological state.

Management

Values and economics dictate animal well being.Available information and experience dictatewhen and how often management intervenes tosupply deficient nutrients. Managers evaluatealternative strategies to meet animalrequirements. Managers experience a continualtradeoff between meeting the needs of theindividual and the herd.

Characterization of Uncertainty

Plant. Availability of nutrients above animalrequirements in different plant tissues drivesthe system. Obviously, the greater the portionof nutrients in the environment aboverequirements, the lower the risk animals willnot find nutrients to meet requirements. If allnutrients are below requirements, managementmust assess the impact of under-nutrition orprovide a supplement.

Animals prefer a variety of plants and plantparts to ensure optimal ingestion rates andavoid non-nutrient toxins or nutrients that act astoxins The range of nutrient content ofindividual plant or plant parts can vary easilyby 100 percent at any time of the year (Figure1). The extreme range of nutrient content ofthe diet also can vary widely at any time of theyear. Note that early in the season, actual dietsare often lower in nutrient concentration thanthe average available; late in the seasonnutrients are only slightly better than average.

The point of this discussion is that what happensto the nutrient content of individual plants withthe advance in season is really irrelevant if theanimal has diet choices. What is important ishow long animals can find enough high qualitynutrients to meet requirements.

Processes that generate patches across alandscape have the potential to create differentdistributions of plant nutrients. As spatial scaleincreases from a small, single patch tolandscapes and regions, more vegetation patchgenerating processes are included. At the sametime, the diversity of the total nutrient bankavailable to free-grazing herbivores increases.Not only is there an opportunity for greatertemporal variation in tissue-nutrient content, butthere is greater opportunity for nutrient renewalfrom recently bitten plants when the size of apasture or home range increases. That is, there isgreater opportunity for the patterns of defoliationand renewal to be asynchronous. One mightexpect that when conditions are dry or very wetthe impact on phenology and nutrient uptakewould be minimal among microsites comparedto intermediate conditions or sequences ofwetting and drying. We all have observed theimpact of year-to-year sequences, i.e., a wet yearfollowing dry years or dry years following wetyears.

The range of available nutrient content amongplants, sites, and years is huge at all times of theyear, especially in the early growing season. Inregions with non-growing season precipitation,the range of available nutrient content amongplants decreases dramatically. The range is aresult of differences in different life forms vs.variation within life forms. In regions withgrowing season precipitation, the range ofavailable nutrient content can be large, becausesome tillers are long shoots and senescing, someare short shoots and senescing, some aregrowing, vegetative short shoots (Figure 1).

Therefore, it is the frequency distribution oramount of nutrients at any point in relation toanimal requirements that's important (Figure 1).Any lack of high quality components in theforage mix constrains the ability of the animal to

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ingest nutrients to complete components of thelife cycle or perform at economical rates. Theamount of high quality forage consumed usuallyis constrained by availability, distribution, andthe physical limitations of prehension andaccessibility (Bailey, 1995). Unlike low qualityforages, intake of high quality forage usually isnot limited by fill or digestibility. However,immature tissue might act as a nutrient toxinearly in the season. Rittenhouse and Rounds(unpublished) found that diet N content was lessthan the average available early in the growingseason, but, later in the growing season, diet Nwas greater than the average available.

We assume herbivores, especially ruminants, cansubstitute among plant-nutrient storage units(plants and plant parts) to obtain a high-qualitydiet. The challenge of the free-grazing animal isto meet the nutritional requirements necessary tocomplete life processes by fmding and ingestingscarce forage with nutrient concentrations higherthan its requirement and mixing it with moreabundant forages with lower nutrientconcentrations. Past explanations of diet contentvs. requirements are irrelevant, because of theanimal's ability to adapt to a variableenvironment. What is important is the point atwhich the animal can no longer find enoughplant tissue greater than requirement to maintaina diet equal to requirement. The implication isthat diet quality is impacted by herbageallowance and the variety of nutrient-storageunits with quality above requirements. Asgrazing management intensifies, animals have anincreased risk of being unable to find highquality nutrients. If animals are not ahie to findenough high quality nutrients in the occupiedpasture, rate of ingestion decreases, and theymust graze longer to compensate (Demment etal., 1987). The key to maintaining a qualityenvironment for the free-grazing herbivore is tomaintain choices. Choices should include avariety of patches on the landscape and choicesof plants and plant parts within patches.

Animal. Variation in requirements of individualsis large. Variation in ingestion and utilization ofnutrients by individuals is large, includingresponse to under- and over-nutrition. Variation

in requirements of individuals in a herd at anypoint in time is large because of differences inphysiological state(s).

The animal component of the system poses twoimportant sources of uncertainty, i.e., thoseassociated with the individual animal and thoseassociated with variation in herd composition.

The range in nutritive value of individual diets isrepresented by a wide statistical distribution, andthe position of any individual in that distributionchanges with time and conditions. Variation intotal ingestion among animals often isrepresented by coefficient of variation (CVs) of30 to 50 percent. The combined effect ofdifferences in DMD ingestion and diet utilizationcan vary by 30 to 50 percent. Digestibilities ofthe same diet by different animals can vary 20 to30 percent. Differences in lignified diet fiber canbe large; however, differences in diet N amonganimals is usually small. Likewise, consider thestandard deviation (SD) of the maintenancerequirements, including variation in basalmetabolic rate (BMR), activity, clinical and sub-clinical disease, upper and lower criticaltemperatures, body condition score (BCS), daysto calving, potential milk production, andbiological type (size, breed, etc.).

Animals exhibit moderate differences in rumenresponse to different mixes of food in the diet(i.e., associative effects.) The amount of dietarydigestible energy obtained from a high fiber dietmixed with a starch-based energy supplementvaries significantly among individual animals.

Herd composition varies widely during theannual cycle. Herd composition is most criticalduring the last third of gestation and the first 60days following parturition. The distribution ofrequirements in the herd is caused by factors likethe percent conception on first estrus and lengthof the breeding season.

Breed-back within a herd in relation to BCSvaries widely (Figure 2). Some cowsconsistently breed back with BCS of 3 or evenless; others require BCS of 5 or more to ensurebreed-back.

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Management. Perhaps the greatest source ofuncertainty in forage-based systems ismanagement. Management controls thebiological type of producing animals,biological type of the sire, the breeding season,disease prevention and control, replacementforages/feeds, and supplemental feeds.Managerial decisions are made in a climate ofeconomic and financial uncertainty,governmental uncertainty, regulatoryuncertainty, and market uncertainty. Thefinancial and managerial skills of theowner/operator are uncertain.

Management determines how many, when,where, and how long animals might occupy anarea. Management restricts choices.Management controls herbage allowance andgrazing pressure.

The question is, "How much is the operatorwilling to pay to gain the last unit of economicmargin from the production system?" Of course,if the system were perfectly deterministic, theanswer is fairly straight-forward. Unfortunately,the system is suffused with uncertainty.

Discussion

Two strategies could be used to address the issueof deficient nutrients. First, treat the issue as anutrient-balance problem, i.e., ingestion vs.requirements. Second, treat the issue as a risk-management problem. These two approachesresult in very different strategies to deal withuncertainty.

In order to deal with uncertainty, the operatorneeds a valuative tool to project system responseinto the future (in this case, the animal system)and a way to determine how far into the future tolet the system run before measuring an indicatorof integrated response. Integrated response toenvironment and managerial decisions might bemeasured as conception rate or time fromparturition to first estrus. An integrated indicatorof response might be body condition score.

Until recently, we lacked a valuative tool thatwould facilitate predictions about the length oftime it would take for an animal to gain or lose abody condition score, given initial conditions, thephysiological state of the animal, theenvironment, and some estimate of diet quality.Production occurs in an environment ofuncertainty. The best possible decisions inregard to dealing with under-nutrition will comefrom the combined use of a valuative tool(model), like NRC 1996, and periodic indicators(measurement) of animal status, like BCS.Obviously, the greater the uncertainty in thesystem, the more difficult it is to represent thestate of the animal adequately, and the moredifficult it is to know when to adjust inputs suchas kind and level of supplement or management.Neither the prediction nor the measurement arewithout error.

How important is it to be correct? What is thecost of taking a measurement (e.g., BCS)? Whatis the cost or benefit of making a timelyadjustment? The greater the days to calving thegreater the flexibility. The closer to calving, themore critical decisions become, especially inregard to supplemental nutrients. Yet, one cannever know. Statistically, the Kalman filter, usedin either the uni-variate or multi-variate case, is avery powerful tool to help determine the actualstatus of the system (Jazwinski, 1970).

Supplementation of grazing animals traditionallyhas been approached as a nutrient balance issue.The goal is to feed sufficient nutrients to replacedeficient nutrients, where deficiency is defmed inrelation to some response goal. However, whichanimal does the manager feed for? the averageanimal? the one that always seems to breed backat BCS 3.0? or, the one that needs BCS 5.0?The nutrient balance approach is mostappropriate when animals are wintered onharvested forage, because diet choice is limitedand nutrient content of food is more or lessuniform (Rittenhouse and Bailey, 1996).

For each grazing environment, the manager mustask additional, fundamental questions. Whatpercentage of the herd should be reproduction vs.disposable animals; for example, yearlings in a

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cow-calf/yearling operation? How muchvariation in the herd is essential to respond toextremes in environmental conditions? Mostmanagers strive for as much genetic uniformityin the herd as possible and then manage tomaintain the maximum uniformity in offspringfor marketing purposes. Is that the best strategyin uncertain environments, or is some optimalvariation in traits desired? Therefore, thetradeoff becomes genetic uniformity vs. the costof feeding to bring all carcasses to uniformitystandard.

Managers treat the supplementation issue fromboth the perspective of the individual animal andthe herd. In reality, we manage the herd toensure a percentage of the animals produce a calfevery year. That means some animals areunderfed and some are overfed. A legitimatequestion is whether the manager would do abetter job of attaining the desired response withinthe herd if she/he knew the stochasticity thatcharacterizes the uncertainty [note the subtlechange in emphasis from meeting requirementsto obtaining the desired response]. For example,would a rancher make better decisions if she/heknew the protein or total digestible nutrients(TDN) content of the average animal's dietthroughout the year vs. making decisions basedon the previous year's herd response to somelevel of feeding? So, the basic question iswhether one is better off to track the diet of theanimal (presumably to know if nutrients ingestedbalance with nutrient demand), or simply toprovide some level of nutrients based onprevious experience, monitor some indicator ofresponse (like BCS), and adjust periodically?

How much of the uncertainty in the system canbe ignored without consequence? If the systemis linear, the cost function is quadratic and allvariables are Gaussian, uncertainty can beignored, and decisions based on averages are justas good as those that include conditionalprobabilities (Jameson, 1985). Is the relationshipbetween level of supplement and BCSmathematically linear (not necessarily a straightline)? Is the economic consequence ofunderfeeding the same as the economic benefitof overfeeding? In this case, the cost function

probably is not quadratic; it probably is skewedto the right. In other words, the cost of a femalenot producing offspring every year is moreimportant than some added increment of cost toensure another calf. At what point are thosecosts equal? Are the variables Gaussian? Mostanalyses show that distributions can be skewedto some extent without materially affecting thedecision.

There seems to be ample evidence thatuncertainty in the environment can be ignored.Decisions based on averages are just as good asdecisions based on the stochasticity of thesystem. The best decisions would be based on asimple prediction of response, based on currentsystem status. Then, the question becomes howlong to let the system run before taking anothermeasurement and adjusting inputs.

I am not aware of a specific analysis to test theabove assumptions/hypotheses. It makes senseto me that one would make better decisionsusing a combination of predicted response andactual measurement of the status of the system(BCS) than tracking inputs, like nutrientcomposition of diets at a point in time based onfecal analysis. Methods like fecal analysis atbest estimate the nutrient composition of thediet of an average herd animal. How doesknowing the nutrient composition of ananimal's diet at a point in time help themanager make better decisions over the nexttime-step? If it helps explain animal responseto an incremental adjustment in level ofsupplement, maybe yes.

Managers use a combination of science andbiology to make production decisions. Theysurround themselves with information, testedideas, and competent advisors. Decisions arecouched in economical and environmentalcontexts. The operator calls on observation andpast experience to modify inputs and projectoutcome/benefit. Each manager is differentand develops very different strategies to dealwith uncertainty. All can be successful to

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varying degrees. Success is measured in manyways. However, there is no strategy thatguarantees against failure. At some point,asynchronous, negative events may all cometogether at the same time and overwhelm thesystem.

Literature Cited

Bailey, D.W. 1995. Daily selection of feedingareas by cattle in homogenious andheterogenious environments. Appi.Anim. Behav. Sci. 45:183-199.

Demment, M.W., E.A. Lada, and G.B.Greenwood. 1987. Intake of grazingruminants: a conceptual framework. In.Symposium Proc. Feed Intake by Cattle.F.N. Owens (ed.). OK. Agr. Exp. Sta.MIP-121, pp. 207-225.

Jameson, D.A. 1985. A priori analysis ofallowable interval betweenmeasurements as a test of modelvalidity. Appi. Math and Computation.17:93-105.

Jazwinski, A.H. 1970. Stochastic processesand filtering theory. Academic Press.New York.

National Research Council. 1996. Nutrientrequirements of beef cattle. NationalAcademy of Sciences. Washington,DC

Rittenhouse, L.R. and D.W. Bailey. 1996.Spatial and temporal distribution ofnutrients adaptive significance to free-grazing behaviors. Proc. GrazingLivestock Nutrition Conference.

Post Script. "In the grand scheme of things,managers who are adaptive survive longer thanthose who are predictive."

Days Post-Partum

Figure 1. Plant and animal uncertainty in the system. Crude protein is an example of limitingnutrient. The solid, narrow lines respresent the range of nutrient concentrations found indifferent plant storage organs and kinds of plants. The dashed line represents the range ofrequirements of individuals in the herd for this nutrient. The solid, wide line representswhat is normally depicted as the potential diet composition of animals under free-grazingconditions. This line is idealized, because animals seldom graze under conditions ofunlimited resource or without competition from cohorts. The inserts represent the potentialdistribution of nutrients within the range of nutrient concentrations (green to gray) andshow how those distributions might change with depletion. The challenge of the animal isto find enough food with nutrient concentration greater than requirements to mix with foodwith nutrient concentration lower than requirements so the weighted average equalsrequirements.

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0

Figure 2. The range of breed-back response of individuals in a herd with different BCS at parturition.Some individuals maintain a 365-thy production cycle with minimal BCS, while others requirehigh BCS to ensure breed-back. Granted the end product (the carcass) must fall within therange of industry standards, but animals should be suited to the available forage resource tomaintain good economic margins and manage economic risk effectively. The huge differencein the level of inputs (cost) required to bring animals to different BCS at parturition depends oninitial conditions. Animals with high requirements absolutely must begin the period of under-nutrition in high BCS, and that must be maintained up to parturition. The cost will be high.The cost of underestimating feed required to meet the goal escalates as animals approachparturition. Animals with low requirements that begin the period of under-nutrition with goodBCS require fewer inputs to maintain enough BCS to breed back. The cost of underestimatingfeed requirements as animals approach parturition is less, because increments of feed are usedmore efficiently.

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