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ABSTRACT: The purpose of this study was to inves-tigate the effects of winter growing program on subse-quent finishing performance, carcass merit, and body composition of beef steers. Four steers were slaughtered to determine initial body composition. Remaining steers (n = 256) were blocked by BW and randomly allotted to 1 of 4 treatment groups: 1) ad libitum fed a high-concentrate diet (CF), 2) grazed on wheat pasture (WP), 3) fed a sorghum silage-based diet (SF), or 4) program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve ap-proximately equal rates of BW gain. After the growing phase (112 d), 6 steers were randomly selected from the WP, SF, and PF treatments for determination of body composition. Remaining steers were adapted to a high-concentrate diet for finishing and slaughtered at 1.27 cm of 12th-rib fat. Six steers from each treat-ment were used to determine carcass, offal, and empty body composition. During the growing phase, WP, SF, and PF steers gained 1.15, 1.10, and 1.18 kg/d, respec-tively, and ME intake did not differ (P = 0.50) among treatments. Program-fed and SF steers had greater (P < 0.05) offal and empty body fat content than WP steers. Gain in offal and empty body fat was greatest (P < 0.05) for PF steers, intermediate for SF steers,

and least for WP steers. During the finishing phase (123, 104, 104, 196 d for WP, SF, PF, and CF, respec-tively) DMI was greater (P < 0.01) for SF steers (10.9 kg/d) than for PF steers (10.1 kg/d); WP steers were intermediate (10.4 kg/d). Daily BW gain was greatest (P < 0.05) for SF steers (2.02 kg/d), intermediate for PF steers (1.85 kg/d), and least for WP and CF steers (1.64 and 1.63 kg/d, respectively). Accretion (kg/d) of carcass and empty body mass was less (P < 0.05) for WP and CF steers compared with PF and SF steers. Calf-fed steers had greater (P < 0.05) fat content of of-fal than SF and PF steers; WP steers were intermediate. Gain in empty body and carcass energy (Mcal/d) was greater (P < 0.05) for PF steers than CF steers with SF and WP steers being intermediate. At slaughter, SF steers had reduced (P < 0.01) yield grades and greater marbling scores compared with CF and WP steers; PF steers were intermediate. In conclusion, growing pro-grams that increase fat composition of feeder calves did not negatively affect subsequent finishing performance. Finishing steers as calves may reduce retained energy of carcass tissues and increase internal fat during high-grain feeding compared with steers that previously un-derwent a growing program.

Key words: beef cattle, body composition, carcass, feedlot performance, growth

©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:1564–1576 doi:10.2527/jas.2009-2289

INTRODUCTION

Previous plane of nutrition, body composition, BW, age, and breed type are all factors that must be consid-

ered when predicting potential finishing performance of feeder cattle (Coleman and Evans, 1986; Coleman et al., 1993). Weaned calves are often placed into a backgrounding or stocker program to achieve adequate

Effects of winter growing programs on subsequent feedlot performance, carcass characteristics, body composition,

and energy requirements of beef steers1,2

M. P. McCurdy,* G. W. Horn,*3 J. J. Wagner,† P. A. Lancaster,* and C. R. Krehbiel*

*Department of Animal Science, Oklahoma State University, Stillwater 74078; and †Southeast Colorado Research Center, Colorado State University, Lamar 81052

1 Approved for publication by the Director of the Oklahoma Agric. Exp. Stn. This material is based in part upon work supported by the Cooperative State Research, Education, and Extension Service, USDA, under Award No. 2003-34198-13358 and 2005-34198-15652.

2 The authors thank D. Perry (Department of Animal Science, Oklahoma State University, Stillwater), K. Whittet (Department of Animal Science, Oklahoma State University), and J. Summers (De-partment of Animal Science, Oklahoma State University) for their help in collection and analysis of samples; S. Schaeffer (Department

of Animal Science, Oklahoma State University), J. Kountz (Depart-ment of Animal Science, Oklahoma State University), and S. Welty (Department of Animal Science, Oklahoma State University) for an-imal care and sample preparation; the Southeast Colorado Research Center staff and animal caretakers; and numerous undergraduate and graduate students who assisted on slaughter dates.

3 Corresponding author: [email protected] July 10, 2009.Accepted December 9, 2009.

1564

Published December 4, 2014

frame size before entering the finishing phase; howev-er, some cattle go directly to finishing after weaning. Rate of BW gain during finishing can be influenced by plane of nutrition and energy density of the diet during the growing phase. Steers that are fed to have greater rates of BW gain during backgrounding are fatter for all measures of carcass composition upon feedlot entry compared with steers that have been nutritionally re-stricted (Baker et al., 1992; Sainz et al., 1995; Hersom et al., 2004a). Cattle that have a greater percentage of body fat upon feedlot entry are generally assumed to be less efficient and to have reduced BW gains during the finishing phase, resulting in a negative correlation between predicted ME allowable ADG and initial BCS (NRC, 1996). However, this assumption may not be valid because fatter cattle are also heavier at feedlot entry and closer to mature size, which would result in reduced growth and efficiency (Owens et al., 1993).

We designed an experiment to test the hypothesis that steers managed for different rates of fat accumu-lation but similar rates of BW gain on different di-ets during backgrounding would have different perfor-mance during the finishing phase. The objective was to determine the effects of winter growing program on subsequent finishing performance, carcass merit, and body composition.

MATERIALS AND METHODS

All procedures for the present study were approved by the Oklahoma State University Institutional Animal Care and Use Committee.

Experimental Animals and Treatments

A total of 260 British crossbred steers were utilized for the experiment. Fifty steers (average initial BW = 239 ± 33.5 kg) from the Oklahoma State University cow herd were weaned in the fall of 2003. The remain-ing 210 steers (average initial BW = 236 ± 22.0 kg) were purchased by Colorado Beef (Lamar, CO) to be of similar breed, type, and age. Four randomly select-ed steers (1 steer from the Oklahoma State University herd and 3 steers from Colorado Beef) were transport-ed to the Oklahoma Food and Agricultural Products Research and Technology Center (FAPRTC) abattoir in Stillwater for an initial slaughter group. Remaining steers were blocked by initial BW and randomly allot-ted to 1 of 4 treatments for winter feeding. One group of steers (CF) was placed in the feedlot (n = 8 pens; 8 steers/pen) immediately on arrival and adapted to a high-concentrate finishing diet fed ad libitum. Steers in this treatment underwent a 3-tier diet adaptation consisting of a 49% concentrate diet for 5 d, 74% con-centrate diet for 7 d, and 88% concentrate finishing diet. The 3 remaining treatment groups were managed on 3 different growing programs to achieve approxi-mately equal rates of BW gain. One group was grazed on wheat pasture with unrestricted forage availability

(WP; n = 3 pastures; 64 steers), a second group was fed a sorghum silage-based growing diet (SF; n = 8 pens; 8 steers/pen), and the third group was program fed (Galyean, 1999) a high-concentrate diet (PF; n = 8 pens; 8 steers/pen). The ingredient composition of the silage-based diet was adjusted after the first 28-d period of the growing phase to adjust rate of BW gain of the SF steers (Table 1). The adjusted silage-based diet was fed for the remainder of the growing phase. Feed delivery for the PF steers was adjusted every 28 d based on 28-d BW measurements and ADG over the previous 28-d period to result in similar rate of BW gain to the SF group based on NRC (1984) equations for medium-frame steers.

Feed bunks were evaluated at 0630 h with a target of a few crumbles of feed remaining at that time. Ex-cluding PF steers, feed delivery was increased 0.23 kg of DM per steer for bunks that were empty 2 consecu-tive mornings. Diets were manufactured immediately before feeding using a 4-auger stationary mixer (Harsh Manufacturing, Dodge City, KS) and delivered twice daily. Feed refusals were weighed and sampled for DM determination on weigh days, whenever feed became spoiled due to adverse weather conditions, and at the conclusion of the trial. Diet and feed commodities were sampled weekly during the trial. A subsample of the diet, feed commodities, and feed refusals was evaluated for DM at the time the sample was collected by drying in a 60°C convection oven for 48 h. Diet and feed com-modity samples were composited by month and nutri-ent composition analyzed by a commercial laboratory (SDK Laboratories, Hutchinson, KS). The composition of each diet is shown in Tables 1 and 2. Nutrient com-position of wheat forage was 90.9% OM, 44.5% NDF, 23.5% ADF, and 21.99% CP on a DM basis.

All pen feeding during the growing and finishing phases took place at the Southeast Colorado Research Center, whereas steers grazed wheat pasture at the Oklahoma State University Wheat Pasture Research Unit (Stillwater). Steers from the Oklahoma State Uni-versity cow herd that were allocated to the SF, PF, and CF groups were transported from Stillwater, OK, to Lamar, CO (688 km), whereas purchased steers al-located to the WP group were transported from Lamar to Stillwater before the beginning of the trial. At both locations, steers were treated for parasites with Ivomec Plus (Merial, Duluth, GA), vaccinated for bovine rhi-notracheitis, bovine viral diarrhea (types 1 and 2), bo-vine syncytial virus, and parainfluenza3 with Titanium 5 (AgriLabs, St. Joseph, MO) and for Clostridium chau-voei-septicum-novyi-sordellii-perfringens type C and D with Vision 7 (Intervet/Schering Plough, De Soto, KS), and implanted with Component ES plus Tylan (20 mg of estradiol benzoate and 200 mg of progesterone, Vetlife, Overland Park, KS). All steers were revacci-nated for bovine rhinotracheitis, bovine viral diarrhea (types 1 and 2), bovine syncytial virus, parainfluenza3, and leptospirosis with Titanium 5 L5 (AgriLabs) ap-proximately 14 d after the start of the trial.

Growing programs and finishing performance 1565

Steers from all treatments were weighed at 28-d inter-vals. Steers in the SF, PF, and CF groups were weighed immediately after removal from their feedlot pens. A 4% pencil shrink was applied to BW from SF and CF steers. Due to the restricted amount of feed received by PF steers, BW from that treatment were pencil shrunk

3% to account for differences in fill. Steers grazing WP were gathered off pasture at approximately 0700 h on weigh days and held in pens without water for 2 to 3 h before weighing. A 2% pencil shrink was then applied to these BW for WP steers. Cravey et al. (1991) measured BW shrink of steers at 5, 10, 17, and 24 h after removal

Table 1. Ingredient and nutrient composition (% of DM unless stated otherwise) of growing and finishing diets fed to steers

Item1

Diet2

SF1 SF2 PF CF

Ingredient composition Steam-flaked corn 25.94 5.73 60.88 76.14 Alfalfa hay — 30.73 — — Sorghum silage 62.56 60.00 23.52 11.76 CCDS3 3.00 3.00 3.00 3.00 Yellow grease — — 3.50 3.50 Soybean meal 7.08 — 5.80 2.26 Supplement 1.42 0.54 3.30 3.35Nutrient composition DM, % of as-fed 38.50 35.53 54.14 63.46 CP 12.58 14.03 14.90 13.34 NPN4 0.98 0.85 3.12 3.13 NDF 32.46 42.94 20.55 14.66 NEm,5 Mcal per kg 1.55 1.31 2.04 2.19 NEg,

5 Mcal per kg 0.97 0.77 1.36 1.51 Calcium 0.82 0.95 0.91 0.78 Phosphorus 0.23 0.21 0.28 0.28 Potassium 1.34 1.92 0.97 0.72 Magnesium 0.25 0.31 0.26 0.26

1Percentage of DM unless stated otherwise.2SF1 = silage diet fed for first 28 d; SF2 = silage diet fed for remainder of the growing phase; PF = program

fed; CF = concentrate diet provided for ad libitum intake.3Condensed corn distillers solubles.4CP equivalent.5Calculated from NRC (1996).

Table 2. Ingredient composition of the supplements used in growing and finishing diets fed to steers

Ingredient1

Diet2

SF1 SF2 PF CF

Limestone 55.32 — 35.16 27.75Urea 11.24 25.44 32.17 31.82Salt 17.59 45.95 7.58 7.47Mg limestone3 9.60 15.79 20.94 27.87Potassium chloride — — — 1.04Mineral oil 2.01 2.03 2.04 2.01Trace mineral premix4 1.33 3.12 0.86 0.80Monensin premix5 1.24 3.33 0.53 0.53Tylosin premix6 0.33 0.84 0.14 0.14Vitamin A premix7 0.21 0.53 0.09 0.09Vitamin E premix8 1.14 2.96 0.49 0.48

1Percentage of DM.2SF1 = silage supplement fed for first 28 d; SF2 = silage supplement fed for remainder of the growing phase;

PF = program fed; CF = ad libitum concentrate fed.3Min Ad Inc., Amarillo, TX. 21.45% Ca and 11.68% Mg, DM basis.4Co, 340 mg/kg; Cu, 7.7%; Mn, 6%; Zn, 22.4%; and Se, 300 mg/kg.5Rumensin, Elanco Animal Health, Greenfield, IN; 176.4 g of monensin per kg of premix, DM basis.6Tylan, Elanco Animal Health; 220.5 g of tylosin per kg of premix, DM basis.7Contained 110,250,000 IU of vitamin A per kg of premix, DM basis.8Contained 198,450 IU of vitamin E per kg of premix, DM basis.

McCurdy et al.1566

from wheat pasture. Shrink increased in a quadratic manner (Y = 0.3186 + 0.6743x – 0.0149x2; R2 = 0.98). From this relationship calculated shrink at 2.5 h equals 1.91%. This value (1.91%) plus the 2% pencil shrink for WP steers is very close to the 4% pencil shrink that was used for the SF and CF steers.

At the end of the growing phase (112 d), 6 randomly selected steers from each of the WP, SF, and PF treat-ments were transported to the FAPRTC abattoir for intermediate slaughter. Remaining steers in the WP group were shipped from Stillwater, OK, to Lamar, CO, for finishing (688 km). Final BW off wheat pas-ture in Stillwater was considered as the final growing phase BW and the initial finishing phase BW for the WP group. Remaining steers from these 3 treatments were adapted to the same high-concentrate finishing diet as CF steers and placed in the feedlot (n = 8 pens; 8 steers/pen). Steers in the WP and SF groups were adapted to the finishing diet as described above for the CF treatment group, whereas PF steers immediately received the 74% concentrate diet for 4 d followed by the 88% concentrate finishing diet.

Steers on the growing diets (WP, SF, and PF) were reimplanted with Revalor-S (120 mg of trenbolone ac-etate and 24 mg of estradiol, Intervet/Schering Plough) at the start of the finishing phase. Calf-fed steers were reimplanted with Revalor-S at d 84 of the finishing phase. During the finishing phase, steers in all treat-ment groups were weighed immediately after removal from their feedlot pens and a 4% pencil shrink was ap-plied to all BW. After the finishing phase, steers from all treatment groups were slaughtered at a common 12th-rib fat thickness of 1.27 cm as determined by ul-trasound. Six randomly selected steers from each treat-ment group were transported to the FAPRTC abattoir for the final slaughter group. Remaining steers in all treatments were slaughtered commercially at the Swift plant in Cactus, TX, and complete carcass data (LM area, 12th-rib fat thickness, KPH, marbling score, and yield grade) were collected by the Cattlemen’s Carcass Data Service (West Texas A&M University, Canyon).

During the growing phase of the study, 4 steers were removed for health concerns that included hardware disease, respiratory illness, and rectal prolapse. Two ad-ditional steers were removed during the finishing phase due to brisket disease and respiratory illness. This re-sulted in 2 steers being removed from each of the SF, PF, and CF treatments.

Slaughter and Sample Collection

Slaughter procedures for cattle that were used for car-cass composition determination and collection of sam-ples were similar for all slaughter groups as described by Hersom et al. (2004a, b). Steers were stunned with captive bolt and exsanguinated. Weights of the blood, head, hide, feet and ears, internal organs, visceral tis-sues (reticulo-rumen, omasum, abomasum, small and

large intestine, cecum, and mesenteric/omental fat), trim, and hot carcass were recorded. Contents of the gastrointestinal tract were removed before weighing. Total offal weight included weight of blood, head, hide, feet and ears, internal organs, visceral tissues, and trim. Empty BW (EBW) was calculated as HCW plus total offal weight.

After weighing, visceral tissues were composited, ground, mixed, and subsampled in triplicate. After sampling, visceral components were composited with blood and remaining offal tissues and ground to mea-sure total offal tissue composition. Tissues were ground twice using an Autio grinder (Autio Co., Astoria, OR) through a 10-mm aperture plate, mixed, and subsam-pled in triplicate. After a 48-h chill, carcass charac-teristics, including maturity, marbling score, 12th-rib fat thickness, 12th-rib LM area, KPH, USDA quality grade, and USDA yield grade were determined. The right side of each carcass was then ground, mixed, and sampled in a similar manner as described for offal tissue to determine carcass and empty body composition.

Chemical Analysis

Chemical analyses of body composition components were carried out using procedures described by Hersom et al. (2004a). Triplicate samples of carcass and offal were analyzed for water by lyophilization to a constant weight. Lyophilized samples were further processed to reduce particle size by submersion in liquid nitrogen and grinding using a Waring blender (Waring Prod-ucts Co., Winsted, CT). Samples were subsequently analyzed for fat (extraction with diethyl ether for 48 h in a Soxhlet apparatus) and fat-free OM (FFOM; combustion of ether extraction residue, 500°C for 6 h). Energy content of tissues was calculated as weight of ether extracted material × 9.4 kcal/g plus weight of FFOM × 5.55 kcal/g (Ferrell and Jenkins, 1998). For calculation of accretion of body tissue components during the growing phase, initial body composition of steers was estimated as average percent composition of the initial slaughter group multiplied by initial BW of each treatment. For calculation of accretion of body tis-sue components during finishing, average composition of the intermediate slaughter group for each treatment was multiplied by the final growing phase BW of each treatment.

Determination of NE Requirements

A group of similar steers were used for the determi-nation of ME contents of the diets for each of the 4 treatment groups. Steers in the CF, SF, and PF groups (n = 5 steers/diet) were fed individually in stalls at the Oklahoma State University Nutrition Physiology Research Center (Stillwater). Steers in the WP group (n = 5 steers) were grazed on a common wheat pasture with the larger group of steers at the Oklahoma State


University Wheat Pasture Research Unit. Diet samples were collected daily, composited, and analyzed for DM, NDF, ADF, CP, and insoluble ash. Total feces and urine were collected for determination of fecal and uri-nary energy and N loss for the CF, SF, and PF treat-ments. Fecal and urine grab samples were collected for WP steers. Fecal output was estimated using chromium oxide as an indigestible marker, and total DMI was estimated as fecal output divided by the percentage of the indigestible portion of NDF of wheat pasture forage. Indigestible NDF of wheat forage was deter-mined by a 96-h in situ digestion (in triplicate) followed by NDF determination of remaining materials. Urine samples from all treatment groups were analyzed for concentration of creatinine by liquid chromatography (Shingfield and Offer, 1999). Total creatinine excretion per day was calculated for CF, SF, and PF groups. The average total creatinine excretion (g/d) for these groups was divided by the creatinine concentration of urine samples (g/mL) from WP steers to determine to-tal daily output of urine for steers in the WP group. Gaseous energy losses associated with methane for all groups were estimated using the equations of Moe and Tyrrell (1980), and heat of fermentation was estimated as 7% of ME (ARC, 1980). Retained energy (RE) was obtained from the energy content of the whole body composition of slaughtered steers and was subtracted from ME intake for determination of daily heat produc-tion. Fasting heat production (FHP) was estimated as the intercept of the regression of ME intake on log heat production. Net efficiency was estimated as the slope of the regression of ME intake on RE.

Statistical Analyses

Data for performance and carcass characteristics were analyzed as a randomized complete block design using generalized least squares (PROC MIXED, SAS Inst. Inc., Cary, NC). Pen or pasture was considered the experimental unit. Steers were classified as USDA Choice+, Choice00, Choice−, Select, or Standard using a binary system (0 or 1). The proportion of steers in each quality grade category was analyzed as a randomized complete block design using a generalized linear mixed model (PROC GLIMMIX, SAS Inst. Inc.) with a bi-nomial distribution. For these data, individual animal was considered the experimental unit. The model for all measurements included treatment as a fixed effect and block (initial BW) as a random effect. Data for energy intake and retention were analyzed as a completely ran-domized design using generalized least squares (PROC MIXED). Individual animal was considered the exper-imental unit and the model included treatment as a fixed effect. Regression of ME intake on RE and ME intake on log heat production was carried out using a regression procedure (PROC REG, SAS Inst. Inc.). Mean separation for all data was accomplished using LSD, and means were considered to be significantly dif-

ferent at the P < 0.05 level when protected by an F-value (P ≤ 0.10).

RESULTS

Performance and Carcass Merit

During the growing phase, ADG was greater (P = 0.01) for WP and PF steers than for SF steers (Ta-ble 3). However, treatment means were 1.15, 1.10, and 1.18 kg/d for WP, SF, and PF steers, respectively, and therefore, our objective of achieving similar rates of BW gain was generally met. Dry matter intake was greater (P < 0.001) for steers fed silage compared with PF steers, whereas G:F was greater (P < 0.001) for PF steers compared with SF steers. At the end of growing phase, HCW tended to be less (P = 0.10) for SF steers compared with PF steers; WP steers were intermedi-ate. Longissimus muscle area was similar (P > 0.10) among treatments. Although not statistically different (P > 0.10), 12th-rib fat thickness and marbling score increased as grain content of the diet increased (WP < SF < PF).

Performance during the finishing phase and carcass characteristics are shown in Table 4. Initial (average = 376 vs. 239 kg, respectively) and final (average = 579 vs. 559 kg, respectively) BW were greater (P < 0.001) for steers that went through a growing program than for calf-fed steers. During finishing, DMI was 7.9% greater (P < 0.001) for SF steers than for PF steers, with WP steers being intermediate. Steers fed as calves had less (P < 0.001) DMI (8.6 kg/d) through slaughter com-pared with all other treatment groups; however, days on the finishing diet were 70 to 84 d longer than for steers initially fed growing diets. Steers in the SF group had 9.2% greater (P < 0.05) ADG than PF steers, and PF steers had 12.8% greater (P < 0.01) ADG than WP and CF steers. This resulted in a reduced (P < 0.01) G:F for WP steers compared with SF, PF, and CF steers.

Hot carcass weight did not differ (P = 0.12) among treatments (Table 4). Dressing percent was greater (P < 0.05) for WP, PF, and CF steers than for SF steers. Calf-fed steers had smaller (P < 0.05) LM area com-pared with SF and PF steers; WP steers were interme-diate. Calf-fed steers had greater (P < 0.01) 12th-rib fat thickness compared with the other treatments. This resulted in less desirable USDA Yield grades for CF and WP steers compared with SF and PF steers (P < 0.05). Steers fed silage during the growing period had greater (P < 0.01) marbling scores, and a smaller percentage graded USDA Select compared with CF and WP steers with PF steers being intermediate. In addition, SF steers had greater (P < 0.05) percentage of steers grad-ing USDA Choice compared with WP and CF steers with PF steers being intermediate (total Choice % = 49.98, 72.00, 54.00, and 41.07 ± 7.07 for WP, SF, PF, and CF, respectively) even though there was no dif-

McCurdy et al.1568

ference between treatments for Choice+, Choice00, or Choice−.

Composition of BW Gain

Average composition of the initial slaughter group is shown in Table 5, and chemical composition and rates of accretion during the growing and finishing phases are

shown in Tables 6 and 7, respectively. After the grow-ing phase, empty body mass did not differ (P = 0.16) among treatments (Table 6). However, FFOM (kg) was greater (P < 0.05) in the carcass of PF steers than WP and SF steers. Mass (kg) of fat and energy (Mcal) in the offal was greatest (P < 0.05) for PF, intermediate for SF, and least for WP steers. When expressed per kilogram of EBW, fat in offal was greater (P < 0.05)

Table 3. Effect of treatment on performance of steers during the growing phase (d 1 to 112) and intermediate carcass characteristics

Item

Treatment1

SEM2 P-valueWP SF PF

Performance Initial BW, kg 253a 237b 234b 2.87 <0.001 Final BW, kg 382 369 377 3.76 0.51 DMI, kg/d — 7.7a 6.1b 0.20 <0.001 ADG, kg 1.15c 1.10b 1.18a 0.02 0.01 G:F, kg/kg — 0.143a 0.198b 0.007 <0.001Carcass characteristic HCW, kg 222.0ab 212.1a 237.2b 7.8 0.10 Dressing % 59.4 57.3 57.8 0.6 0.11 12th-rib fat, cm 0.44 0.51 0.59 0.07 0.32 LM area, cm2 63.8 60.3 65.0 3.0 0.53 KPH, % 0.3 0.6 0.5 0.1 0.24 Marbling score3 245 273 305 20.6 0.15

a–cWithin a row, means without a common superscript letter differ (P < 0.05).1WP = wheat pasture; SF = silage fed; PF = program fed.2SE of least squares means, n = 3 for WP, n = 8 for SF and PF, n = 6 for carcass characteristics.3200 = USDA Traces00, 300 = USDA Slight00.

Table 4. Effect of treatment on performance of steers during the finishing phase and carcass characteristics at slaughter

Item

Treatment1

SEM2 P-valueWP SF PF CF

Performance Days on feed 123 104 104 196 — — Initial BW, kg 382a 369b 377ab 239c 3.76 <0.001 Final BW, kg 584a 581a 571ab 559b 6.22 <0.001 DMI, kg/d 10.4ab 10.9a 10.1b 8.6c 0.24 <0.001 ADG, kg 1.64a 2.02b 1.85c 1.63a 0.04 <0.001 G:F, kg/kg 0.156a 0.186b 0.186b 0.190b 0.005 <0.001Carcass characteristic HCW, kg 386 379 376 371 4.4 0.12 Dressing % 65.9a 65.1b 65.9a 66.3a 0.27 0.01 12th-rib fat, cm 1.35a 1.27a 1.24a 1.63b 0.048 <0.001 LM area, cm2 86.5ab 89.7a 89.0a 84.5b 1.29 0.02 KPH, % 3.0 3.0 3.0 3.1 0.05 0.41 Yield grade 3.19a 2.76b 2.94b 3.39a 0.08 <0.001 Marbling score3 409a 449b 423ab 401a 9.8 0.01 Choice+, % 0.00 6.07 5.96 1.81 3.55 0.71 Choice00, % 12.00 16.00 12.00 7.14 5.18 0.58 Choice−, % 37.98 49.93 36.04 32.12 7.29 0.29 Select, % 48.00a 28.00b 46.00ab 58.93a 7.06 0.02 Standard, % 2.02 0.00 0.00 0.00 2.00 0.99

a–cWithin a row, means without a common superscript letter differ (P < 0.05).1WP = wheat pasture; SF = silage fed; PF = program fed; CF = ad libitum concentrate fed.2SE of least squares means, n = 8 for performance and carcass characteristics, n = 208 for percent quality

grade.3400 = USDA Small00, 500 = USDA Modest00.


for PF and SF steers compared with WP steers. Simi-lar results were observed for fat (g/kg of EBW) and energy (Mcal) in the empty body. Fat-free OM (kg) in the empty body was greatest (P < 0.05) for PF, inter-mediate for WP, and least for SF steers. However, no differences (P = 0.16) were observed when FFOM was expressed per unit of EBW.

During the growing phase, PF steers accreted carcass and empty body mass (kg/d) at a greater (P < 0.05) rate than WP and SF steers, suggesting that a greater percentage of BW gain for WP and SF steers was due to gastrointestinal tract fill (Table 6). Similarly, steers in the PF group accreted FFOM at a greater rate (g/d; P < 0.05) in the carcass and empty body compared with SF and WP steers. Program-fed steers accreted fat (g/d) and energy (Mcal/d) in offal and empty body at a greater rate (P < 0.05) than WP steers; SF steers were intermediate, which is consistent with the objec-tive of this experiment.

After the finishing phase, mass of carcass, offal, and empty body did not differ (P > 0.10) among treat-ments (Table 7). In addition, chemical compositions of the carcass and empty body at the end of the finish-ing phase were similar (P > 0.10) among growing pro-grams. In general, offal FFOM was less (P < 0.05) and offal fat was greater (P < 0.05) as a proportion of EBW for CF steers compared with steers backgrounded be-fore finishing. During the finishing period, carcass and empty body gain were greater (P < 0.05) for SF and PF steers than for WP and CF steers. Offal gain was greater (P < 0.05) for PF steers compared with WP and CF steers during finishing. Gain of FFOM followed a similar trend as mass for the carcass, offal, and empty body. In contrast, gain of fat did not differ (P = 0.28) among treatments during the finishing period. Energy gain in the carcass and empty body was greatest (P < 0.05) for PF, intermediate for WP and SF, and least for CF.

Data for ME intake and energy retention are shown in Table 8. Metabolizable energy intake (Mcal/d) of the growing diets did not differ (P = 0.50) among the WP, SF, and PF treatments during the metabolism ex-periment and was relatively similar between treatments

during the growing phase based on the similar ADG. Steers in the PF group had greater (P < 0.05) RE (Mcal/d) in the empty body compared with WP steers, with SF steers being intermediate. The same trend in RE of the empty body was also observed in individual components (carcass, offal, viscera). Therefore, heat production for steers in the PF treatment was signifi-cantly (P < 0.05) less than WP and SF steers. Metabo-lizable energy intake of the finishing diet was greater (P < 0.05) for SF steers than for PF steers, and PF steers had greater (P < 0.05) ME intake compared with CF steers. The ME intake of the WP treatment was inter-mediate to SF and PF steers and significantly greater (P < 0.05) than the CF treatment. These differences in ME intake of the finishing diet during the metabo-lism experiment are similar to those for DMI of steers during the finishing phase. Consistent with the least ME intake, CF steers also had the least RE (Mcal/d). Steers in the PF treatment had the numerically great-est RE in the empty body and in the carcass, despite a decreased ME intake as compared with WP and SF steers. The estimated daily heat production of PF and CF steers was less (P < 0.05) than WP and SF steers. Steers in the PF group had the smallest FHP numeri-cally, but there were no statistical differences. Com-pared with WP and SF steers, PF steers had greater net efficiency (P < 0.05).

DISCUSSION

Feeder cattle that are fatter typically garner price discounts (Smith et al., 2000) compared with leaner cattle because of expected decreased performance and efficiency during the finishing phase. However, Sainz et al. (1995) and Hersom et al. (2004a) reported that calves exhibiting greater fat composition at feedlot en-try did not have reduced finishing ADG or G:F com-pared with calves with less fat composition at feedlot entry. In the present experiment, calves that were fat-ter at feedlot entry had improved finishing ADG and G:F compared with calves that were leaner at feedlot entry. In addition, results from the present study indi-cate that calves that were fatter at feedlot entry had greater gains of carcass protein and energy during the finishing phase.

Evaluation of Growing Diets

Growing Phase. Growing treatments were de-signed to provide similar energy intake and, thus, simi-lar ADG, with an increasing proportion of energy from concentrate (WP < SF < PF) that would result in differences in body fat content. Rate of BW gain dur-ing the growing phase was slightly less for the SF treat-ment than WP and PF steers, but there was a linear increase in offal fat with increasing energy from concen-trate, and SF and PF steers had greater empty body fat than WP steers at the end of the growing phase.

Table 5. Chemical composition of the initial slaughter group of steers

Item

Tissue component

Carcass OffalEmpty body

BW, kg 140.2 76.0 216.3Water, kg 72.0 42.0 114.0FFOM,1 kg 33.4 18.7 52.1FFOM, g/kg 237.2 247.0 240.6Fat, kg 25.6 11.2 36.9Fat, g/kg 181.5 146.1 168.9Energy,2 Mcal 425.8 209.6 635.4

1FFIN = fat-free OM.2Ether extract material × 9.4 kcal/g + FFOM × 5.55 kcal/g.

McCurdy et al.1570

Tab

le 6

. E

ffec

t of

win

ter

grow

ing

prog

ram

on

chem

ical

com

posi

tion

and

com

posi

tion

of B

W g

ain

of s

teer

s du

ring

the

gro

win

g ph

ase

Item

Car

cass

Offal

Em

pty

body

Tre

atm

ent1

SEM

2

Tre

atm

ent

SEM

Tre

atm

ent

SEM

WP

SFP

FW

PSF

PF

WP

SFP

F

Che

mic

al c

ompo

sition

BW

, kg

222.

021

2.1

237.

27.

8311

4.2

110.

511

6.6

3.85

336.

232

2.6

353.

810

.77

Wat

er, kg

128.

3ab11

8.0a

130.

3b3.

7269

.064

.366

.52.

4919

7.3

182.

419

6.8

5.15

FFO

M,3

kg46

.6a

45.9

a53

.7b

2.45

23.5

21.8

23.3

1.12

70.1

ab67

.7a

77.0

b2.

76 F

FO

M, g/

kg20

9.4

216.

522

5.9

5.62

205.

819

6.7

201.

39.

2620

8.1

209.

521

7.8

3.66

Fat

, kg

33.6

36.2

40.0

3.03

16.8

a19

.9ab

22.3

b1.

6450

.356

.162

.33.

98 F

at, g/

kg15

1.2

169.

016

8.3

9.90

146.

6a18

0.6b

189.

6b10

.84

149.

8a17

2.9b

174.

1b7.

66 E

nerg

y,4 M

cal

573

595

674

36.7

288a

308ab

339b

14.7

862a

903ab

1,01

3b48

.5 E

nerg

y, M

cal/

kg2.

592.

792.

840.

082.

52a

2.79

b2.

90b

0.07

2.56

a2.

79b

2.86

b0.

07C

ompo

sition

of B

W g

ain

BW

, kg

/d0.

81a

0.80

a0.

96b

0.04

40.

390.

390.

420.

031.

20a

1.19

a1.

38b

0.06

5 W

ater

, g/

d54

2ab48

5a56

4b24

.926

424

525

021

.780

673

081

437

.4 F

FO

M, g/

d13

9a15

2a20

7b16

.053

5258

9.6

192a

204a

265b

16.7

Fat

, g/

d87

126

149

22.0

57a

89ab

105b

12.8

144a

215ab

255b

28.1

Ene

rgy,

Mca

l/d

1.59

a2.

03ab

2.55

b0.

235

0.83

a1.

12ab

1.32

b0.

102.

42a

3.15

ab3.

87b

0.30

a,b W

ithi

n a

row

and

tis

sue,

mea

ns w

itho

ut a

com

mon

sup

ersc

ript

let

ter

differ

(P

< 0

.05)

.1 W

P =

whe

at p

astu

re; SF

= s

ilage

fed

; P

F =

pro

gram

fed

.2 S

E o

f le

ast

squa

res

mea

ns, n

= 6

.3 F

FO

M =

fat

-fre

e O

M.

4 Eth

er e

xtra

ct m

ater

ial ×

9.4

kca

l/g

+ F

FO

M ×

5.5

5 kc

al/g

.


Tab

le 7

. E

ffec

t of

win

ter

grow

ing

prog

ram

on

chem

ical

com

posi

tion

and

com

posi

tion

of B

W g

ain

of s

teer

s du

ring

the

fin

ishi

ng p

hase

Item

Car

cass

Offal

Em

pty

body

Tre

atm

ent1

SEM

2

Tre

atm

ent

SEM

Tre

atm

ent

SEM

WP

SFP

FC

FW

PSF

PF

CF

WP

SFP

FC

F

Che

mic

al c

ompo

sition

BW

, kg

376.

035

7.1

383.

436

1.1

14.6

217

5.0

165.

517

5.3

166.

66.

4455

1.1

522.

555

8.7

527.

620

.56

Wat

er, kg

182.

517

3.5

182.

317

0.2

6.07

89.6

87.8

90.0

83.8

3.15

272.

126

1.4

272.

225

4.0

8.96

FFO

M,3

kg86

.884

.389

.688

.14.

0435

.4a

32.2

ab35

.5a

29.7

b1.

1512

2.2

116.

512

5.1

117.

84.

74 F

FO

M, g/

kg23

1.3

236.

023

4.3

243.

87.

2020

2.3a

194.

6ab20

4.1a

178.

3b5.

7922

2.1

223.

122

4.9

223.

15.

88 F

at, kg

84.5

81.7

91.8

84.0

8.03

43.4

39.6

43.1

46.8

3.27

127.

912

1.3

134.

813

0.9

10.7

8 F

at, g/

kg22

3.0

227.

623

6.0

232.

615

.60

247.

6ab23

9.3a

240.

9a28

1.8b

13.1

723

0.9

231.

323

7.5

248.

413

.75

Ene

rgy,

4 M

cal

1,27

61,

235

1,36

01,

279

86.5

605

551

602

605

33.3

1,88

11,

786

1,96

11,

884

115.

7 E

nerg

y, M

cal/

kg3.

383.

453.

523.

540.

133.

453.

333.

403.

640.

113.

403.

413.

483.

570.

11C

ompo

sition

of B

W g

ain

BW

, kg

/d1.

18a

1.46

b1.

57b

1.23

a0.

070.

45a

0.56

bc0.

64c

0.52

ab0.

031.

63a

2.02

b2.

21b

1.75

a0.

94 W

ater

, g/

d39

5a56

7b58

6b55

3b38

.614

3a24

6b27

0b24

4b17

.553

7a81

3b85

6b79

6b53

.5 F

FO

M, g/

d31

2a38

3b38

3b30

4a23

.988

ab10

7bc13

1c69

a8.

840

0a49

0b51

3b37

3a24

.7 F

at, g/

d40

245

152

531

761

.621

119

521

619

024

.861

364

674

250

882

.2 E

nerg

y, M

cal/

d5.

51ab

6.37

ab7.

06b

4.67

a0.

612.

472.

432.

762.

170.

227.

98ab

8.80

ab9.

82a

6.84

b0.

79a–

c Withi

n a

row

and

tis

sue,

mea

ns w

itho

ut a

com

mon

sup

ersc

ript

let

ter

differ

(P

< 0

.05)

.1 W

P =

whe

at p

astu

re; SF

= s

ilage

fed

; P

F =

pro

gram

fed

; C

F =

ad

libitum

con

cent

rate

fed

.2 S

E o

f le

ast

squa

res

mea

ns, n

= 6

.3 F

at-fre

e O

M.

4 Eth

er e

xtra

ct m

ater

ial ×

9.4

kca

l/g

+ F

FO

M ×

5.5

5 kc

al/g

.

McCurdy et al.1572

Therefore, the growing treatments resulted in the de-sired outcomes.

Similar to the results of this study, previous stud-ies have reported changes in empty body fat content in response to dietary manipulations during the grow-ing phase. Carstens et al. (1991) and Wright and Rus-sel (1991) reported that nutrient restriction resulted in cattle with less empty body fat content than those not restricted. Carstens et al. (1991) reported less car-cass and noncarcass fat for nutrient-restricted steers, whereas Wright and Russel (1991) reported only less noncarcass fat. However, in these previous experiments nutrient intake was altered by limiting intake of the same diet such that growth rate was altered, whereas, in our study, nutrient intake was altered by changing diet composition and maintaining similar energy intake and rate of BW gain.

Coleman et al. (1995a) and Sainz et al. (1995) com-pared body composition of steers limit-fed grain-based diets to silage- or forage-fed steers, respectively, fed for similar growth rate during the growing phase. Sainz et al. (1995) reported greater carcass, noncarcass, and empty body fat content for the steers limit-fed a grain-based diet, whereas Coleman et al. (1995a) reported greater fat content of noncarcass tissue only. These data are similar to our results in that increasing grain con-tent of the growing diet resulted in greater fat content of the empty body. In addition, Hersom et al. (2004a) reported that steers grazing wheat pasture had greater carcass, noncarcass, and empty body fat content than steers grazing winter native range; however, these steers were not managed for similar rates of growth.

Finishing Phase. In our study, SF and PF steers had greater ADG and G:F compared with WP steers

during the finishing phase, even though SF and PF steers were fatter at feedlot entry. Hersom et al. (2004a) reported similar ADG and G:F during finishing for steers previously grazing wheat pasture or native win-ter range, whereas Gill et al. (1993a) reported great-er ADG and G:F for steers previously grazing wheat pasture compared with winter native range. Choat et al. (2003) reported greater ADG and G:F for steers previously grazed on native winter range than winter wheat. Hersom et al. (2004a) reported that empty body fat content was greater for steers previously grazing wheat pasture, whereas Gill et al. (1993c) reported similar empty body fat content. However, steers previ-ously grazed on native range had similar empty BW as steers in the study of Gill et al. (1993c). Choat et al. (2003) did not report body fat composition at the start of finishing, although fat content likely differed as evidenced by the greater growing ADG and initial BW of wheat pasture steers. Coleman et al. (1995b) reported similar finishing ADG and G:F between steers that were fed silage- and grain-based diets during the growing phase, but reported greater empty BW gain for silage-fed steers. In contrast, Sainz et al. (1995) re-ported greater empty BW gain and empty BW G:F for steers limit-fed grain-based diets compared with steers fed forage-based diets. In our study, empty BW gain was similar between PF and SF steers, but greater than WP steers. Hersom et al. (2004a) reported that grow-ing diet had no effect on empty BW gain during the finishing phase.

Previous studies (Sainz et al., 1995; Hersom et al., 2004a) have reported similar final carcass characteris-tics for steers previously fed different diets during the growing phase when fed to a similar compositional end

Table 8. Energy intake and retention in the empty body (Mcal/d) by steers during growing and finishing phases

Item

Treatment1

SEM2 P-valueWP SF PF CF

Growing phase ME intake 12.89 13.25 12.63 — 0.37 0.50 Retained energy 2.42a 3.15ab 3.87b — 0.30 0.02 Carcass 1.59a 2.03ab 2.55b — 0.24 0.04 Offal 0.83a 1.12ab 1.32b — 0.10 0.02 Viscera 0.33a 0.48a 0.68b — 0.06 0.004 Heat production 10.47a 10.10a 8.76b — 0.48 0.05Finishing phase ME intake 28.36ab 29.96a 27.07b 23.42c 0.79 <0.001 Retained energy 7.98ab 8.80ab 9.82a 6.84b 0.79 0.09 Carcass 5.51ab 6.37ab 7.06a 4.67b 0.61 0.06 Offal 2.47 2.43 2.76 2.17 0.22 0.35 Viscera 1.49 1.36 1.41 1.01 0.19 0.33 Heat production 20.37a 21.16a 17.25b 16.57b 0.93 0.004 Fasting heat production3 0.78 0.76 0.75 — 0.03 0.09 Net efficiency4 0.36a 0.34a 0.46b — 0.06 0.04

a–cWithin a row, means without a common superscript letter differ (P < 0.05).1WP = wheat pasture; SF = silage fed; PF = program fed; CF = ad libitum concentrate fed.2SE of least squares means, n = 6.3Calculated as the intercept of the regression of log heat production on ME intake.4Calculated as the slope of retained energy on ME intake.


point. In our study, WP steers had greater yield grades than SF and PF steers, and reduced marbling scores and percent USDA Choice than SF steers, although this may be due to increased stress from an additional transport of WP steers from Stillwater, OK, to Lamar, CO, at the end of the growing phase. Gardner et al. (1999) reported that cattle with lung lesions at slaugh-ter had smaller LM area and decreased KPH and mar-bling score. Choat et al. (2003) reported that steers previously grazing wheat pasture had greater LM area, KPH, and marbling score, but similar yield and quality grade as steers previously grazing native winter range. Gill et al. (1993b) reported that carcass characteristics were similar between steers previously grazing wheat pasture or native range. Similarly, Winterholler et al. (2008) reported similar percent USDA Choice+ and to-tal Choice for steers backgrounded on wheat pasture compared with calf-fed steers.

Sainz et al. (1995) reported that final empty body fat and protein composition and fat gain were similar among growing treatments; however, steers limit-fed a grain-based diet during the growing phase had greater empty body protein gain during the finishing phase. Our results showed similar final chemical composition of the carcass, offal, and empty body among growing treatments after the finishing phase, although SF and PF steers had greater empty body FFOM gain than WP steers, similar to the results of Sainz et al. (1995). In contrast, Hersom et al. (2004a) reported similar final empty body fat and protein composition and empty body FFOM and fat gain between growing treatments in Exp. 1, but in Exp. 2 steers grazing wheat pasture had reduced final empty body fat composition and empty body fat gain due to less carcass and offal fat gain during the finishing phase. Carstens et al. (1991) reported that steers previously nutrient restricted had greater carcass, noncarcass, and empty body protein and less carcass, noncarcass, and empty body fat con-tent at the end of the finishing phase than steers not previously restricted. Wright and Russel (1991) report-ed less noncarcass fat content for steers previously nu-trient restricted, but similar carcass and empty body fat and protein content. Furthermore, Wright and Rus-sel (1991) reported similar empty body fat and protein gain between growing treatments during the finishing phase, but decreased carcass fat gain and greater car-cass protein gain for steers with no previous nutrient restriction with corresponding reduced noncarcass fat gain and greater noncarcass protein gain. In our study carcass and offal fat gain were similar, but carcass and offal FFOM gain were greater for SF and PF steers than WP steers. Growing treatments in the studies of Carstens et al. (1991), Wright and Russel (1991), and Hersom et al. (2004a) were designed to limit nutrient in-take to alter rate of growth, whereas, in the present ex-periment and in Sainz et al. (1995), growing treatments altered nutrient intake but maintained similar growth rates. Thus, the differences among growing treatments in body composition at the end of the finishing phase

may be a result of degree of nutrient restriction or sub-sequent compensatory gain.

Collectively, these data call into question the concept that cattle which are fatter at feedlot entry will have reduced performance and efficiency during the finishing phase. In our study and Sainz et al. (1995), fatter steers had improved ADG and G:F during the finishing phase. In addition, Hersom et al. (2004a) observed that fatter cattle had similar rates of BW gain and G:F compared with leaner cattle when fed to a common compositional end point. In contrast, Choat et al. (2003) reported decreased finishing ADG and G:F for fatter calves. Fur-thermore, final carcass characteristics and body compo-sition were not significantly altered by growing treat-ment except in the study by Choat et al. (2003). The current findings generally agree with Klopfenstein et al. (2000) who concluded that there were no differences in carcass quality due to type of backgrounding program or rate of BW gain during the growing/backgrounding phase when steers were finished to a common 12th-rib fat thickness.

Metabolism Study. Metabolizable energy intake of the growing diets was similar during the metabo-lism experiment. There was a linear increase in RE as grain content of the diet increased most likely due to the increased empty body fat gain observed during the growing phase. Program-fed steers had less heat pro-duction than WP and SF steers. Sainz et al. (1995) also reported less heat production for steers limit-fed a grain diet compared with forage-fed steers. Similarly, Reynolds et al. (1991) reported decreased heat produc-tion for heifers fed a 75% concentrate diet compared with those fed a 75% alfalfa hay diet.

Program-fed steers had the least ME intake of the finishing diet and the greatest RE in the empty body, giving the least estimate for daily heat production. This would suggest that heat increment, maintenance requirements, or both were greater for WP and SF steers compared with PF steers. In fact, PF steers had greater efficiency of ME use than WP and SF steers. This agrees with the work of Sainz et al. (1995) that showed a 21% reduction in maintenance requirements during the finishing phase for steers limit-fed a high-concentrate diet during the growing phase compared with steers ad libitum-fed a forage diet during the growing phase. However, estimates of FHP were not different between treatments in this study.

Calf-fed vs. Backgrounding

The CF treatment was included to allow comparisons in finishing performance with steers that previously un-derwent a backgrounding phase. In general, CF steers had less DMI and ADG, but similar G:F compared with steers that were previously fed a growing diet. Ridenour et al. (1982), Gill et al. (1993a), and Winter-holler et al. (2008) reported that calves placed on a fin-ishing diet at weaning had decreased ADG, but greater G:F during the finishing period than those placed on

McCurdy et al.1574

a growing diet before finishing. Lancaster et al. (1973) and Sainz et al. (1995) reported that calves placed on a finishing diet at weaning had greater ADG during the growing phase, but reduced ADG during the finishing phase than calves placed on a growing diet during the growing phase. Similar results were reported for G:F (Sainz et al., 1995). Overall ADG was similar between the treatments in the study of Lancaster et al. (1973), but overall ADG was greater for calves placed on the finishing diet, whereas overall G:F was similar in the study of Sainz et al. (1995). Although not compared statistically, when overall ADG and G:F values for CF steers were compared with finishing phase values for the calves placed on a growing diet at weaning, CF steers had reduced ADG and greater G:F (Lancaster et al., 1973; Sainz et al., 1995). In addition, previous studies have reported reduced growth rate (Myers et al., 1999a; Meyer et al., 2005) and improved efficiency (Myers et al., 1999a) of early weaned steers placed on a high-concentrate diet compared with traditionally weaned steers.

In this study, steers that were placed on a finish-ing diet at weaning had less final BW and tended to have less HCW than steers that underwent a growing program before finishing. Gill et al. (1993b) reported reduced HCW for steers placed on a finishing diet at weaning compared with those previously grazed on wheat pasture or native range. Wertz et al. (2001) re-ported that heifers finished as calves had reduced HCW than those finished as yearlings after a grazing period. In contrast, Lancaster et al. (1973) and Ridenour et al. (1982) observed similar final BW and HCW between steers placed on a finishing diet at weaning and those backgrounded before finishing. Ridenour et al. (1982) reported that steers placed on a high-concentrate diet at weaning had similar 12th-rib fat thickness, quality, and yield grade but greater KPH and LM area, whereas Lancaster et al. (1973) reported greater 12th-rib fat thickness and quality grade but similar KPH and LM area. Gill et al. (1993b) reported similar 12th-rib fat thickness, KPH, and yield grade, but reduced marbling scores compared with steers placed on a growing diet or grazed on pasture before finishing. Sainz et al. (1995) observed that steers placed on a finishing diet at wean-ing had greater fat thickness, less KPH, and similar yield grade and marbling score compared with steers placed on a growing diet before finishing. Winterholler et al. (2008) reported similar fat thickness, KPH, yield grade, marbling score, and percent USDA Choice be-tween steers that previously grazed wheat pasture and those placed on feed at weaning. In our study, CF steers generally had greater 12th-rib fat thickness and yield grade, smaller LM area, similar marbling score, and decreased percent USDA Choice. In contrast, Myers et al. (1999b) reported no differences in carcass character-istics between early weaned steers placed on a finishing diet or those grown on pasture before feedlot entry. In addition, our results and those of Sainz et al. (1995) indicate that placing steers on a high-concentrate diet

at weaning did not alter carcass fat content or emp-ty body fat or protein content compared with steers placed on a growing diet before finishing. However, in our study, CF steers had greater offal fat content than the other treatments. Collectively, these data show in-consistent differences in carcass characteristics between calf-fed and previously backgrounded steers. However, these data suggest that finishing steers as calves may not improve carcass quality, which supports the find-ings of Klopfenstein et al. (2000).

Calf-fed steers had less RE than PF steers with WP and SF steers being intermediate; although, CF steers also had reduced ME intake. Thus, the proportion of ME intake retained in the empty body (RE divided by ME intake) was numerically similar between CF steers and the other treatments (0.29 vs. 0.28, 0.29, and 0.36 for WP, SF, and PF steers, respectively). Sainz et al. (1995) reported similar results (0.21 vs. 0.23 and 0.26 for calf-fed, forage-fed, and limit-fed treatments, re-spectively).

In conclusion, our results suggest that growing pro-grams which increase body fat composition will not negatively affect subsequent feedlot performance and efficiency. Furthermore, when fed to a common 12th-rib fat end point, growing programs that alter body composition before finishing will not significantly alter carcass quality or body composition at final slaughter. However, program feeding of a high-concentrate diet during the growing period may result in greater BW gains, increased RE in the empty body and carcass, and greater efficiency of ME use to achieve similar car-cass quality as compared with forage-based growing programs even at similar calculated ME intake. Plac-ing steers on a high-concentrate diet at weaning may not alter final carcass composition or improve carcass quality compared with steers placed on a growing diet before finishing. Moreover, calf-fed steers may not be more energetically efficient during finishing than steers previously backgrounded.

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