effect of stay-green ranking, maturity and...
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EFFECT OF STAY-GREEN RANKING, MATURITY AND MOISTURE CONCENTRATION OF CORN HYBRIDS ON SILAGE QUALITY AND THE HEALTH AND PRODUCTIVITY
OF LACTATING DAIRY COWS
By
KATHY GISELA ARRIOLA
A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2006
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Copyright 2006
by
Kathy Gisela Arriola
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To my adorable son Wilhelm Andre.
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ACKNOWLEDGMENTS
I would like to thank my supervisory committee members, Dr. Adegbola Adesogan, Dr.
Charles Staples and Dr. Lynn Sollenberger, for their guidance, valuable time, patience and
dedication to my research during my M.S. program. Special thanks are expressed to Dr.
Adegbola Adesogan for his trust in my abilities not only as a student but also as a person, before
and during my M.S. program.
I would also like to thank all my laboratory supervisors and partners (John Funk, Jan
Kivipelto, Nancy Wilkinson, Pam Miles, Max Huisden, Dervin Dean, Nathan Krueger, Sam-
Churl Kim, Jamie Foster, Susan Chikagwa-Malunga, Mustapha Salawu, Tolu Ososanya, Sergei
Sennikov and Ashley Hughes) for their help during my laboratory and field activities.
I would like to also thank my parents (Jackson and Martha Arriola) for their continuous
support, patience and dedication through each important step in my life. Thanks go to my
brothers (Jackson, Ricardo and Ines) for their support and for keeping my faith alive.
I thank my husband, Julio Alberto, who has been there unconditionally for me through
endless hours in the laboratory and field.
Finally, I thank my son, Wilhelm Andre, who has been my daily inspiration.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS ...............................................................................................................4
LIST OF TABLES...........................................................................................................................7
LIST OF FIGURES .........................................................................................................................8
ABSTRACT.....................................................................................................................................9
CHAPTER
1 INTRODUCTION ..................................................................................................................11
2 LITERATURE REVIEW .......................................................................................................13
Factors Affecting the Nutritive Value of Corn Plants ............................................................13 Hybrid..............................................................................................................................13
Brown midrib hybrids ..............................................................................................14 Grain digestibility (flint vs. dent hybrids) ................................................................14 High-oil hybrids .......................................................................................................17 High-grain yield and leafy hybrids...........................................................................20
Cutting Height .................................................................................................................21 Maturity ...........................................................................................................................24
Digestibility..............................................................................................................27 Animal performance.................................................................................................28
Factors Affecting the Fermentation of Corn Silage................................................................29 Maturity ...........................................................................................................................30 Inoculants ........................................................................................................................30 Chop Length ....................................................................................................................32 Processing........................................................................................................................32 Chemical Additives .........................................................................................................33
Factors Affecting Aerobic Stability of Corn Silage ...............................................................33 Yeasts ..............................................................................................................................33 Molds and Mycotoxins ....................................................................................................34 Microbial Inoculants........................................................................................................36 Ammonia .........................................................................................................................38
Hemorrhagic Bowel Syndrome ..............................................................................................39 Variable Manure Syndrome....................................................................................................40 Stay-green Corn Hybrids ........................................................................................................41
3 EFFECT OF MATURITY AT HARVEST OF CORN HYBRIDS DIFFERING IN STAY-GREEN RANKING ON THE QUALITY OF CORN SILAGE ................................46
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Introduction.............................................................................................................................46 Materials and Methods ...........................................................................................................47
Plot Trial ..........................................................................................................................47 Planting and establishment.......................................................................................47 Fractionation and ensiling. .......................................................................................48 Chemical analysis.....................................................................................................48
Statistical Analysis ..........................................................................................................50 Results and Discussion ...........................................................................................................50
Yield and Chemical Composition of the Unensiled Whole Plant Samples.....................50 Chemical Composition of the Unensiled Stover Samples...............................................51 Chemical Composition of the Unensiled Ear Samples....................................................52 Chemical Composition of Corn Silage Samples .............................................................53 Fermentation Indices of Corn Silage Samples ................................................................54
Conclusions.............................................................................................................................55
4 EFFECT OF STAY-GREEN RANKING, MATURITY AND MOISTURE CONCENTRATION OF CORN SILAGE ON THE HEALTH AND PRODUCTIVITY OF LACTATING DAIRY COWS .........................................................................................67
Introduction.............................................................................................................................67 Materials and Methods ...........................................................................................................68
Diets.................................................................................................................................69 Sample Collection and Analysis......................................................................................69 Statistical Analysis ..........................................................................................................72
Results and Discussion ...........................................................................................................73 Chemical Composition of Corn Silage............................................................................73 Voluntary Intake..............................................................................................................74 Milk Production and Composition ..................................................................................75 Body Weight and Plasma Metabolites ............................................................................77 Rumen Parameters and Health Indices............................................................................77
Conclusions.............................................................................................................................79
5 GENERAL SUMMARY........................................................................................................94
LIST OF REFERENCES...............................................................................................................98
BIOGRAPHICAL SKETCH .......................................................................................................114
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LIST OF TABLES
Table page 3-1 Yield and chemical composition of unensiled whole plants from corn hybrids
differing in stay-green (SG) ranking, maturity and source. ...............................................58
3-2 Chemical composition of unensiled stovers from corn hybrids differing in stay-green (SG) ranking, maturity and source.....................................................................................60
3-3 Chemical composition of unensiled ears from corn hybrids differing in stay-green (SG) ranking, maturity and source.....................................................................................62
3-4 Chemical composition of corn silages made from hybrids differing in stay-green (SG) ranking, maturity and source.....................................................................................63
3-5 Fermentation indices of corn silages silages made from hybrids differing in stay-green (SG) ranking, maturity and source...........................................................................65
4-1 Ingredient and chemical composition of the diets .............................................................81
4-2 Chemical composition of corn silages differing in maturity, SG ranking and moisture treatment at ensiling (n=4) .................................................................................................82
4-3 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on feed intake and digestibility of lactating dairy cows. ..........83
4-4 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on milk production and composition from lactating dairy cows. ..................................................................................................................................84
4-5 Effect of maturity and moisture addition to corn silages with contrasting stay-green (SG) rankings on body weight and plasma metabolites in lactating dairy cows. ..............85
4-6 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on rumen parameters and health indices of lactating dairy cows. ..................................................................................................................................86
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LIST OF FIGURES
Figure page 4-1 Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal fluid pH. ..........................................................................87
4-2 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal NH3-N concentration.......................................................88
4-3 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal acetic acid molar percentage. ..........................................89
4-4 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal propionic acid molar percentage. ....................................90
4-5 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal butyric acid molar percentage. ........................................91
4-6 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal acetic: propionic acid ratio..............................................92
4-7 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal total VFA concentration..................................................93
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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
EFFECT OF STAY-GREEN RANKING, MATURITY AND MOISTURE CONCENTRATION OF CORN HYBRIDS ON SILAGE QUALITY AND THE HEALTH AND PRODUCTIVITY
OF LACTATING DAIRY COWS
By
Kathy Gisela Arriola
December 2006
Chair: Adegbola Adesogan Major Department: Animal Sciences
Two experiments were conducted to evaluate how maturity affects the nutritive value of corn
(Zea mays L.) hybrids with contrasting (stay-green) SG rankings and the performance of dairy
cattle. Experiment 1 determined how maturity affects dry matter (DM) yield, nutritive value, and
aerobic stability of 2 corn hybrids differing in SG ranking from each of two companies. The
hybrids were harvested at 25, 32, and 37 g DM/100g from four replicated plots and separated into
thirds for ear vs. stover chemical analysis, whole plant chemical analysis, and ensiling. The latter
was ensiled (15 kg) in quadruplicate in 20-L mini-silos for at least 107 d. The best combination of
DM yield, nutritive value, fermentation quality and yeast counts was obtained when the corn
hybrids were harvested at 32 g DM/100g. The higher SG ranking changed the moisture
distribution of hybrids from both companies in different ways, reduced the nutritive value of
hybrids from one company, but did not affect silage fermentation and aerobic stability.
Experiment 2 determined the effect of SG ranking and maturity of corn hybrids on the
health, feed intake and milk production of dairy cows. Two corn hybrids with high (Croplan
Genetics 691, HSG) and low (Croplan Genetics 737, LSG) SG rankings were harvested at 26
(Maturity 1) or 35 g DM/100g (Maturity 2) and ensiled in 32-ton plastic bags for at least 77 d.
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Each of silage was fed in ad libitum amounts as part of a total mixed ration consisting of 35, 55
and 10% (DM basis) of corn silage, concentrate and alfalfa (Medicago sativa L.) hay,
respectively to 30 Holstein cows (92 average days in milk). The experiment was a completely
randomized design with two 28-d periods. Harvesting corn silage at 35 instead of 26 g DM/100g
increased the efficiency of feed utilization for milk production but decreased or tended to
decrease intakes of CP and NDF, apparent digestibility of NDF and starch and milk yield. The
higher SG ranking was associated with poorer feed intake and nutrient digestion, but it did not
adversely affect any of the health indices that were monitored.
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CHAPTER 1 INTRODUCTION
Several dairy producers in Florida have experienced considerable losses in milk production
in the past few years due to Variable Manure Syndrome and Hemorrhagic Bowel Syndrome.
Many producers believe that these problems are caused by corn silage with high stay-green (SG)
ranking. Stay-green hybrids have asynchronous ear and stalk dry down rates, therefore their ears
turn brown and their kernels dry down and mature faster than their stalks and leaves which remain
green. Thomas and Smart (1993) characterized a SG trait (i.e., the phenotypes that exhibit delayed
senescence) as having higher water and chlorophyll concentration in the leaves at maturity.
Therefore, high SG rankings are genetically correlated with high stalk and leaf moisture
concentrations (Bekavac et al., 1998). The presence of this characteristic implies that the
traditional relationship between whole plant silage, moisture and kernel milk line may no longer
hold because it probably results in silages that have milk lines that are more advanced relative to
whole-plant maturity (Bagg, 2001). This could lead to either harvesting the corn plant when it is
really too wet or to disease infestation due to delaying the harvest till the stalks get drier.
Harvesting forages when they are too wet or too dry makes the silage susceptible to effluent losses
and respiration losses, respectively (Barnett, 1954). Crops ensiled with excess moisture are often
poorly fermented due to proliferation of butyric acid-producing clostridia. It is also difficult to
ensile crops with excessive DM concentrations because they are difficult to consolidate adequately
in the silo, and the residual oxygen in the silo hinders the fermentation.
Corn varieties without the SG characteristic are no longer readily available commercially
because most current hybrids have the SG phenotype. Only two studies have investigated the
effect of SG hybrids on the performance of dairy cattle and in sheep. However, these experiments
did not compare a SG variety with a conventional variety and they did not determine how the SG
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ranking affects the ideal maturity at harvest of corn silage. Therefore, there is a need to determine
the ideal maturity stage for harvesting SG corn hybrids that are widely used for silage production.
The aim of this study was to determine the effect of maturity at harvest on the nutritive value of the
corn silage hybrids with contrasting SG rankings, and to determine the effect of feeding corn
silages differing in SG ranking, maturity and moisture concentration on the performance of dairy
cattle.
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CHAPTER 2 LITERATURE REVIEW
Factors Affecting the Nutritive Value of Corn Plants
Hybrid
Corn silage is one of the most popular forages fed to dairy cows because it has good
agronomic characteristics; it has high concentrations of key nutrients, ensiles well, and
incorporates easily into the total mixture ration (TMR). In the past, much emphasis was placed
on the total yield of dry matter and amount of grain produced from corn hybrids. Other
traditional criteria for selecting corn hybrids have been based primarily on agronomic factors,
including disease and lodging resistance and drought tolerance. However these measurements
alone are poor indicators of nutritive value (Cox and Cherney, 2001). More recent criteria
utilized for hybrid selection include fiber and starch digestibility in order to maximize milk
production per hectare or milk production per ton of silage (Hunt et al., 1993; Barriere et al.,
1995).
In selection of corn hybrids, more emphasis has been placed on grain production than
silage production. Grain producers have been reluctant to select hybrids based on nutritional
quality because this attracts relatively little economic value. Yet hybrid selection for agronomic
potential and nutritive value is one of the most important management decisions influencing corn
silage production and subsequent milk yields (Allen et al., 1997). Xu et al. (1995) reported that
corn silage hybrid and maturity affected the DM concentration of various plant parts including
leaves, ear, husk, stalk and stover. Johnson et al. (2001) harvested corn hybrids 3845 and Quanta
at one-third milkline, two-thirds milkline, and blackline stages of maturity and found that hybrid
3845 had greater concentrations of ADF (P < 0.0001), NDF (P < 0.0001) and lignin and lower (P
< 0.001) concentrations of starch, non fiber carbohydrates (NFC), and crude protein (CP) than
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Quanta. Some current areas of focus in hybrid selection that have nutritional implications will be
discussed in the following paragraphs.
Brown midrib hybrids
The recent focus of most of the genetic improvement of corn silage has been on enhancing
fiber digestibility in order to increase DM intake (DMI) and milk yield by the dairy cow. The
genetic variability in ruminal cell-wall digestion of corn stover has prompted numerous studies
on this topic (Hunt et al., 1992; Flachowsky et al., 1993; Verbic et al., 1995; Tovar-Gomez et al.,
1997). A land mark discovery in the search for more digestible corn silage was the identification
of the Brown midrib (BMR) trait. About 40 years after their initial discovery, BMR mutations
were found to have a major effect on lignin concentration (Lechtenberg et al., 1972) leading to
improved digestibility of corn silage by ruminants. Brown midrib hybrids contain less lignin in
the stalks and leaves than normal hybrids, resulting in greater stover digestibility and in vitro true
digestibility (IVTD) (Lechtenberg et al., 1972; Colenbrander et al., 1973).
Some studies have shown that BMR hybrids gave substantially lower DM yields and
produce 10 to 15% less DM (Frenchick et al., 1976; Miller and Geadelman, 1983; Cherney et al.,
1991; Allen et al., 1997), and had increased susceptibility to lodging (Cherney et al., 1991).
Feeding studies with BMR corn silage have resulted in greater milk yields (Rook et al., 1977;
Block et al., 1981; Stallings et al., 1982). However, others have reported no improvement in
milk yield after feeding BMR hybrids (Rook et al., 1977; Block et al., 1979; Stallings et al.,
1982). According to Oba and Allen (1999), DMI, yield of milk, protein, fat and lactose were
greater for cows fed a bm3 corn hybrid vs. a control hybrid, but milk fat concentration was not
changed. Some authors (Frenchick et al. 1976; Block et al., 1981) reported milk fat depression
when bm3 corn silage was fed, but others (Rook et al., 1977) reported an increase in milk fat
concentration.
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Bal et al. (2000) evaluated Pioneer 3563 as a conventional hybrid (CH) and Cargill F657 as
a BMR hybrid in feeding trials with lactating dairy cows. They found lower NDF, ADF and
lignin concentrations for BMR vs. CH. Dry matter intake was not different between treatments
groups, perhaps due to higher forage concentration in the BMR diet. Milk production was lower
for cows fed the bm3 than the CH hybrids. Milk fat percentage was greater by 0.08 percentage
units and milk fat yield was greater by 0.28 kg/d in cows fed the bm3 diet compared to the CH
diet.
Cox and Cherney (2001) stated that though BMR hybrids have high NDF digestibility,
which is positively correlated with in vitro true digestibility (IVTD), they do not recommend
their use because of inconsistent milk yields and high seed costs. In one study, the lack of
response to total tract NDF digestibility was attributed to greater DMI for the bm3 mutant
treatment (Rook et al., 1977), because total tract digestibility declines as feed intake increases
(Tyrell and Moe, 1975). Greater DMI for brown midrib hybrids might be associated with a
faster rate of digesta passage, diminishing potential digestibility. Brown midrib 3 (bm3) is a
gene mutation that has been incorporated into corn plants to improve fiber digestibility. This
bm3 mutation resulted from structural changes in the caffeic acid O-methyltransferase (COMT)
gene, which encodes the enzyme O-methyltransferase (COMT; EC 2.1.1.6) involved in lignin
biosynthesis. Therefore, the lignin biosynthesis in bm3 is restricted and structural carbohydrates
are more accessible by ruminal microorganisms.
Oba and Allen (2000) showed that, in spite of increased in vitro NDF digestibility (NDFd),
bm3 corn silage did not have greater NDF digestibility in vivo than the control silage in the
rumen, postruminally, or in the total tract. This indicates that in vitro NDFd does not necessarily
closely predict NDF digestibility in vivo or energy density of forages. These authors noted that
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the bm3 corn silage had a greater passage rate for indigestible NDF and NDF, and surmised that
enhanced in vitro digestibility of NDF might indicate greater fragility of plant cell wall and
reduced physical fill in the rumen, thereby increasing DMI.
Ballard et al. (2000) compared three corn hybrids, namely 1) Mycogen TMF94 (Mycogen),
a leafy hybrid developed for corn silage, 2) Cargill F337 (Cargill), which is a BMR hybrid, and
3) Pioneer 3861 (Pioneer), which is a dual purpose hybrid for silage and grain yield. Using a
plot trial, they found no differences in plant population, infected ears, or lodged plants between
hybrids. However, it should be noted that there was no excessive rain or heavy winds late in the
season. The Cargill F337 hybrid had a higher DM and NDF digestibilities but a lower DM yield
than the Mycogen TMF94 hybrid, and a lower DM concentration than the Pioneer hybrid. The
Cargill hybrid had the highest in vitro true dry matter digestibility (IVTDMD) and in vitro
neutral detergent fiber digestibility (IVNDFD), which were attributed in part to the lower lignin
concentration compared with Mycogen and Pioneer hybrids. During a subsequent feeding trial
no differences were observed in DMI by cows fed the diets based on the Mycogen and Cargill
hybrids, even though the Cargill hybrid was more digestible in vitro. Cows fed the Cargill
silage-based TMR had greater yield of milk and 3.5% FCM compared with cows fed the
Mycogen silage-based TMR. This may be attributed to the higher in vitro digestibility of the
Cargill hybrid, which suggests that more energy was available from the Cargill silage than the
Mycogen or Pioneer silages.
Grain digestibility (flint vs. dent hybrids)
Few studies have reported the ruminal starch digestion of corn silage hybrids. Verbic et al.
(1995) and Philippeau and Michalet-Doreau (1997) reported a large variation in the ruminal
degradation of dent and flint corn grain genotypes. Dent type corn grains tend to have a greater
percentage of floury endosperm, whereas flint type corn grains have a greater percentage of
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vitreous endosperm. In the vitreous endosperm, the starch granules are surrounded by a protein
matrix which limits digestion, whereas those in floury endosperm, starch granules are more
available for digestion (Kotarski et al., 1992). The site of digestion of dietary starch strongly
influences the nature of the end products of digestion and how starch is utilized by the animal
(Nocek and Tamminga, 1991; Huntington, 1997). Therefore knowledge of the rate of ruminal
starch degradation of a hybrid is important in ration formulation.
Some authors reported that the lower in situ degradability of starch in flint corn was caused
by a lower proportion of the rapidly degradable fraction, a lower rate constant of degradation, or
both (Michalet-Doreau and Champion, 1995; Verbic et al., 1995; Philippeau and Michalet-
Doreau, 1997). Philippeau and Michalet-Doreau (1998) evaluated the influence of genotype and
ensiling of corn grain on the rate and extent of ruminal starch degradation using two cultivars of
corn that differed in texture of the endosperm; that is, dent (Zea mays, ssp. indentata) and flint
(Zea mays, ssp. indenture). They found that for unensiled samples, ruminal DM degradability
was similar for both hybrids, but ruminal starch degradability differed (72.3 vs. 61.6% for dent
and flint genotypes, respectively). This was mainly due to a difference in the rapidly degradable
fractions (34.8 and 9.9%) of the respective hybrids. The difference in ruminal starch
degradability between these two hybrids also could be explained by the difference in the grain
DM content for dent (46.4%) and flint (52.3%) genotypes.
High-oil hybrids
Many studies have reported that milk production from dairy cattle can be increased by
replacing dietary conventional corn and supplemental fats with high-oil corn (Palmquist and
Jenkins, 1980; Casper and Schingoethe, 1989; Schingoethe and Casper, 1991). The
polyunsaturated fatty acids in many supplemental fat sources are biohydrogenated in the rumen,
and they can inhibit the growth of cellulolytic ruminal microbes. Using oilseeds such as soybean
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(Glycine max) or high-oil corn (HOC) as the fat source may slow the release of oil into the
rumen and lessen ruminal biohydrogenation (Aldrich et al., 1997), which may minimize ruminal
disturbances while still delivering fatty acids to the animal. High-oil corn is typically reported to
contain 7 to 8% ether extract on a DM basis, nearly double the concentration found in
conventional corn hybrids (CH), whereas protein concentration is typically 1 to 2% units higher
(Dado, 1999). Dietary feeds that contain lipids with low susceptibility to ruminal
biohydrogenation (e.g., oilseeds vs. free oil) can influence milk fatty acid composition
(Grummer, 1991; Palmquist et al., 1993; Avila et al., 2000). Milk from cows fed HOC contained
more unsaturated fatty acids than milk from cows fed conventional corn (Elliot et al., 1993;
LaCount et al., 1995), even though Weiss and Wyatt (2000) reported that ear (cob + kernels), as
a percentage of whole plant DM, was similar between conventional (57%) and high-oil (55%)
hybrids.
Lysine and other essential amino acid (AA) concentrations in HOC are slightly higher
compared with regular corn because HOC contains more germ protein. However, lysine is still
markedly deficient for milk production when HOC is fed. Because lipids contain about 2.25
times the number of calories as a similar weight of carbohydrate, HOC contains about 4% more
gross energy than does regular corn. However HOC may contain more NDF than regular corn,
which may be a potential limitation to its nutritional value (Drackley, 1997).
Smaller amounts of endosperm in HOC kernels result in less starch in both grain and silage
compared with normal corn grain and silage (68 vs. 71% of the grain DM; Hammes, 1997).
Because oil is not fermentable in the rumen and starch is, a smaller quantity of starch in HOC
may result in less microbial growth and protein synthesis, though it could also decrease the
incidence of acidosis (Dado, 1999; Andrae et al., 2000). Feeding trials with HOC for various
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livestock indicate that feeding HOC improves feed efficiency and increases rate of gain over
livestock fed conventional corn (Lambert, 2001).
Whitlock et al. (2003) evaluated the performance of dairy cows fed conventional corn or
HOC-based on TMR. They found no differences between the 2 groups in DMI, milk production,
milk fat concentration, and milk protein concentration. The concentration of short-chain fatty
acids (4:0 to 12:0) in milk was not affected by corn source; however, the concentration of
medium-chain fatty acids (14:0 to 16:1) decreased (P < 0.01) and the concentration of long-chain
fatty acids (17:0 to 22:6) increased (P < 0.01) when cows were fed the HOC. Unsaturated fatty
acid concentration increased (P < 0.01) and saturated fatty acid concentration decreased (P <
0.03) when cows were fed the HOC diets compared with the CC diets.
According to Weiss and Wyatt (2000) the total digestible nutrients (TDN) concentration of
diets with unprocessed HOC silage was about 5% higher than for those with conventional
unprocessed corn silage. However, when the silage was processed, the TDN concentration of
HOC silage was similar to that of conventional silage. Kernel processing increased TDN
concentration of the conventional corn silage diet by 5.3%, but had no effect on TDN
concentration of diets based on HOC silage. Assuming no associative effects, unprocessed HOC
silage had 8.2% more TDN than unprocessed conventional corn silage and processing increased
TDN of the conventional corn silage by 8.4%. The increased TDN of HOC corn silage was
largely caused by increased fat concentration and that of processed corn silage was largely
caused by increased starch digestibility. Dry matter intake was not affected by treatment, though
processed silage had higher starch and non-fiber carbohydrate (NFC) digestibility than
unprocessed silage. Milk yields were similar between processing treatments when high oil corn
silage was fed, and no interaction was observed between varieties and processing for FCM yield.
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The variety of corn silage did not affect milk fat concentration or yield, but cows fed HOC silage
produced milk with less protein.
High-grain yield and leafy hybrids
Most researchers have related maximum DM yield and quality with high grain
concentration (Phipps et al., 1979; Coors et al., 1997). However, corn hybrids have been
developed to have more leaves, which should lead to improved digestibility and better animal
performance (Tolera and Sundstol, 1999; Cox and Cherney, 2001). Thomas et al. (2001)
reported that Novartis NX3018 corn hybrid (selected for increased leaf proportion and
digestibility) had a higher proportion of stover and lower proportion of grain compared with
their Novartis NF29-F1 dual-purpose corn hybrid despite the use of similar plant populations,
their similar DM yields, and similar percent barren and lodged plants. Even though the nutrient
composition of the two corn hybrids was relatively similar, NX3018 had higher IVTDMD and
IVNDFD both before and after ensiling in mini silos and silage bags. Cows that were fed a TMR
containing NX3018 corn silage produced more milk, 3.5% FCM, milk CP, and milk lactose
compared with cows that were fed the TMR containing N29-F1 corn silage. Bal et al. (1998),
however, reported that cows fed TMRs containing leafy or high-grain corn silages had similar
milk yields. Bal et al. (2000) evaluated Mycogen TMF106, a leafy hybrid (LFY), and Pioneer
3563, a conventional hybrid (CH) in a feeding trial with lactating dairy cows. Each hybrid was
planted at low and high plant populations. They found that the moisture concentration of LFY
was higher than that of CH at both plant populations. A diet containing the LFY hybrid diet
resulted in lower DMI and higher milk fat percentage compared with one containing the CH
hybrid, though milk yield did not differ among treatments. Apparent digestibilities of DM,
organic matter (OM), ADF and NDF were higher for diets containing CH than LFY.
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Kuehn et al. (1999) grew and fed 3 corn hybrids: 1) Mycogen TMF94, (94-d maturity) a
leafy hybrid, 2) Dekalb 442 (Dekalb Genetics Corp., Dekalb, IL; 95-d maturity), a high grain
hybrid, and 3) Dahlco No. 2 blend (Dahlco Seeds, Inc, Cokato, MN; 90-d maturity), a blend of
hybrids. They found that NDF and ADF concentration did not differ among the three hybrids
and starch concentration of the high grain silage (26.1% DM basis) was greater than that of the
blend (23.8% DM basis) and leafy (23.5% DM basis) silages. The leafy silage had greater
IVNDFD compared with the other hybrids. Dry matter intake by lactating cows was not affected
by dietary treatment during the third and fourth weeks of the study, though cows fed the leafy
silage had a lower DMI than did cows fed the high grain silage diet. Multiparous cows fed the
high grain silage diet consumed more DM during Week 5 of lactation than cows receiving the
blend or leafy silage diets. Dietary treatment did not affect yields of milk and 3.5% FCM, or
milk composition.
Clark et al. (2002) compared a leafy hybrid (Mycogen TMF94) selected for its silage yield
and leafiness (94-d maturity) with a high grain corn hybrid (Pioneer 3751) selected for its high
yield for grain or silage (99-d maturity). They observed that the leafy corn hybrid used in the
diet for silage at a level of 42% of dietary DM, supported higher DMI as well as increased milk,
4% FCM and milk protein yield compared with a control grain type hybrid variety. When used
in the diet as high moisture shelled corn, the leafy corn hybrid stimulated higher DMI, but no
difference in milk yield, 4% FCM yield, or milk composition was observed.
Cutting Height
Increasing the cutting height of corn plants decreases silage yield but increases nutritive
value because the lower portion of the corn plant is less digestible (Tolera and Sundstol, 1999).
Corn silage yield decreased by 15% as the cutter bar was raised from 15.2 to 45.7 cm above
the soil surface; however, silage quality (milk per ton) increased (Lauer 1998). Cummins and
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Burns (1969) reported that corn forage yields decreased by about 18% but that IVTD increased
by 60 g kg¯1 as cutting height increased from 15 to 90 cm. Harvestable digestible DM (IVTD x
yield) was the same at 15-, 45-, and 90-cm cutting heights (6.0, 6.0, and 5.9 t ha-1, respectively).
According to Curran and Posch (2001), as cutting height increased from 10 to 50 cm, the yields
of eight dual-purpose hybrids decreased by 11%, whole-plant IVTD increased by 16 g kg¯1, NDF
digestibility increased by 8 g kg¯1, and starch concentration increased by 27 g kg¯1.
Consequently, calculated milk yields decreased by only 3.7%, and Curran and Posch concluded
that cutting height management can influence corn forage quality and potential animal
performance.
Lewis et al. (2004) compared the predicted animal response to harvest date and cutting
height of three corn hybrids, Pioneer 34B23 (dual purpose), Mycogen TMF108 (leafy), and
Cargill F757 (brown midrib), harvested at cutting heights of 15, 30 and 46 cm, respectively.
They reported that calculated milk yields from TMF108 did not differ as cutting height increased
from 15 to 46 cm because the increase in milk per ton of silage or forage quality offset the
decline in DM yields. In contrast, calculated milk yields for F757 decreased with increasing
cutting height because the additional removal of highly digestible stover reduced forage quality
and further reduced the inherently low DM yields. This shows that responses to cutting height
changes depend on hybrid stover digestibility.
Starch concentrations did not change as cutting height increased from 15 to 30 cm but
increased by 11g kg-1 as cutting height increased from 30 to 46 cm (Lewis et al., 2004). Average
stover and whole-plant NDF digestibility increased by about 15 to 20 g kg-1 with each 15-cm
increase in cutting height. Average stover IVTD increased by 16 g kg-1 as cutting height
increased from 15 to 30 cm but remained unchanged as cutting height increased to 46 cm.
23
Average whole-plant IVTD increased by a consistent 8 g kg-1 with each successive increase in
cutting height. Although stover CP concentrations increased by 4 g kg-1 as cutting height
increased from 15 to 30 cm, cutting height did not affect whole-plant CP concentrations. Neylon
et al. (2002) also reported only a small change in whole-plant CP concentration of leafy hybrids
as cutting height was increased from 13 to 46 cm.
Bernard et al. (2004) evaluated two corn hybrids, Pioneer 31G20 and Pioneer 32K61 that
had similar ratings for yield and nutrient concentration. Half of the forage on plots containing
each variety was cut at a height of 10.2 cm (normal) and the remaining half was cut at a height of
30.5 cm (high). They reported that corn silage harvested at 30.5 cm had lower concentrations of
ADF compared with that harvested at 10.2 cm, but there were no differences in concentrations of
NDF or IVTDMD. There was an interaction between cutting height and variety because of
increased IVTDMD for 31G20 harvested at 30.5 cm compared with that harvested at 10.2 cm.
No differences in milk yield, milk concentration, yield of milk fat and protein, or energy-
corrected milk yield (ECM) were observed among varieties or cutting heights.
In a trial utilizing several leafy corn silage hybrids harvested at two maturities, Neylon and
Kung (2002) found that increasing the cutting height of corn silage from 12.7 cm, normal cut
(NC), to 45.7 cm, high cut (HC), improved nutritive value by decreasing the concentrations of
ADF, NDF, and ADL but increasing the concentration of starch. In vitro NDF digestibility after
30 h of incubation was affected only by height of cutting and was greater in HC (50.7%) than in
NC (48.3%). Kruczynska et al. (2001) observed a reduction in crude fiber and ADF, and greater
effective degradability of silage that was cut at 50 vs. 10 cm.
Dominguez et al. (2002) evaluated two corn hybrids, brown midrib (bm3) corn silage cut at
a normal height of 23 cm, and conventional corn silage cut at height of 23 cm (NC) or 71 cm
24
(HC). They reported that HC had greater DM concentration than NC (40.9 vs. 38.4%), but HC
had lower NDF concentration (33.9 and 38.6%). No differences in milk yield were found.
Most of these studies indicate that forage digestibility and animal performance is enhanced
at cutting heights of 45 to 50 cm. but is at the expense of DM yield.
Maturity
Whole corn plants are harvested, ensiled, and fed to lactating dairy cattle throughout the
United States (Johnson et al., 1999). However, the nutritive value of corn silage is affected by
the fibrous (stover) portion and grain portions (kernel). As the corn plant matures, the ratio of
stover to grain decreases, and digestibility of the whole plant tends to increase until two-thirds
milk line (ML) (Johnson et al., 1999). This is because maturity of corn at harvest influences
DM, WSC, NDF and starch concentration and IVDMD (Russell, 1986; Tolera et al., 1999). The
NDF concentration of whole plant corn silage declined as maturity advanced from milk to ½ ML
(Ganoe and Roth, 1992; Wiersma et al., 1993), and plateaued (Wiersma et al., 1993) or declined
(year 2, Ganoe and Roth, 1992) as maturity advanced from ½ ML to black layer (BL). As kernel
fill increased from ⅔ ML to BL, DM digestibility decreased in whole-plant corn silage both in
vitro (Hunt et al., 1989) and in vivo (Bal et al., 1997) despite an increase in starch concentration
and a decrease in fiber concentration (Harrison et al., 1996; Bal et al., 1997).
Bal et al. (1997) evaluated the effect of harvesting corn silage at four stages of maturity on
the performance of dairy cows. They found that moisture concentration declined from 69.9 to
58.0% as maturity of the corn advanced from the early dent (ED) stage to the BL stage; and
concentrations of NDF and ADF declined while starch concentration increased. However, no
decline in NDF and ADF concentration or increase in starch concentration was observed from
the ⅔ ML stage to the BL stage.
25
Poor starch fill (and grain yield) can cause photosynthetic energy to remain as sugar in the
stover and leaves, thus diluting fiber content but not yielding the expected net energy (Fairey,
1983; Coors et al., 1997). Johnson and McClure (1968) reported an increasing concentration of
soluble carbohydrate in stalks from tasseling to the milk stage and this declined thereafter.
According to Darby and Lauer (2002), the relationship between DM yield and growing
degree units (GDU) is linear. The nutritive value of unfermented forage and silage increased and
stover quality decreased as harvest time progressed through the growing season. Generally,
forage quality was always lowest when harvest time coincided with flowering. Fiber
constituents were lowest between 1100 and 1110 GDU (650 g kg-1 of moisture). In vitro true
digestibility was maximized at 1025 GDU (700 g kg -1 of moisture). Milk per ton of silage and
milk per hectare were optimized at 1075 and 1105 GDU (670 and 630 g kg-1 of moisture),
respectively. Therefore, these authors suggested that yield, quality and performance indices will
remain at 95% of the optimum values if corn forage is harvested between 700 and 600 g kg-1 of
moisture.
Hunt et al. (1989) reported that corn DM yield and quality were greater at 315 vs. 390 g kg-
1 of DM concentration in an irrigated California study. Wiersma et al. (1993) reported that DM
yield and IVDMD of corn forage were greater at 330 vs. 260 g kg-1 of DM concentration in a
Wisconsin study. According to Wiersma et al. (1993), CP concentration declined rapidly with
increasing maturity, averaging a drop of 2 percentage units from soft dough to no ML for whole
corn plants and 3 percentage units for stover. Decreasing CP concentration appears to be the
result of continued carbon assimilation, even though N uptake probably was completed, thereby
diluting plant N concentration. Stover fiber concentration increased by an average of 3.2 and 2.9
percentage units of NDF and ADF respectively during the period from soft dough to no ML.
26
Whole plant fiber concentration generally declined from soft dough to ½ ML and then plateaued
after ½ ML. Decreases in whole plant fiber concentration from soft dough to ½ ML averaged
7.6 and 4.4 percentage units for NDF and ADF, respectively.
Stage of maturity has important effects on many characteristics of corn crops grown for
silage. Total crop yield, grain and DM concentration, stover digestibility (Daynard and
Hunter,1975), ensiling losses (Giardini et al., 1976), and silage intake (Malterre, 1976) can all be
influenced by crop maturity and are important considerations in corn silage production. For
many years, corn was harvested for silage when the kernels reached the BL stage of
development. Recently, the recommendation has been to harvest corn plants when the ML is
half to three quarters of the way down the kernel. This was based on observations that corn
forage harvested at these stages contained more grain, had higher digestibility and higher yields
compared to corn harvested at the BL stage (Wiersma et al., 1993). Huber et al. (1965) reported
an increase in silage DMI and in milk production of cows as the maturity of whole-plant corn at
harvest advanced from the soft stage to the hard dough stage and Harrison et al. (1996) found
higher milk production for cows fed silage from whole-plant corn harvested at the one-half milk-
line stage versus the BL stage. Havilah et al. (1995) reported that the maximum yield of the crop
was produced at milk line score (MLS) 3.4, and harvesting at MLS 2-3 (under Australian
conditions) would provide near maximum yield, optimum DM content for ensiling, and high
digestibility.
Whole-crop DM concentration has been a useful determinant of the correct stage of
harvest. The ideal DM concentration for the coincidence of optimum DM yield, ensiling
suitability, and feed quality is in the range of 300 - 400 g/kg (Wiersma et al., 1993). Within this
range adequate compaction and preservation of silage can be achieved. Harvesting forages when
27
they are too wet or too dry makes the silage susceptible to effluent losses and respiration losses,
respectively (Barnett, 1954). Ensiling crops with lower DM concentration also poses a risk of
poor fermentation while adequate paking of high DM crops in the silo is difficult, and typically
results in increased ensiling losses (Havilah et al., 1995).
Dairy producers with bunker silos typically begin corn silage harvest at DM concentration
of about 300 g kg-1, about 50 g kg-1 wetter than the target DM for silage stored in upright silos,
because silage effluent production from bunker silos is minimal at DM concentration of 300 g
kg-1 and above (Bastiman and Altman, 1985).
Digestibility
As with all forages, the digestibility of the stover portion of corn silage declines
dramatically with progressive maturity. Nonstructural carbohydrates and IVDMD decreased and
fiber concentration increased in stover with advancing maturity (Russell, 1986). Russell et al.
(1992) reported that IVDMD of corn stover decreased with advancing maturity and was highly
correlated with ADF and lignin concentrations. The increasing proportion of grain as the corn
plant matures obscures the relationship between plant maturity and digestibility of whole plant
corn silage. Hunt et al. (1989) studied maturity effects of six corn hybrids across 2 yr and two
locations. Concentrations of NDF and ADF in the whole plant decreased as maturity proceeded
from early one-third ML to mid two-thirds ML, and did not change from mid to late BL
maturity.
Cummins (1970) reported that whole plant digestibility increased with advancing plant
maturity until DM concentration reached 35 to 40%, but Daynard and Hunter (1975) found
whole plant digestibility to be constant from 24 to 44% DM concentration. This discrepancy
could be due to differences between the corn hybrids examined.
28
One of the factors that alter the digestibility of corn silage is the vitreous endosperm in corn
kernels within the corn silage. The vitreous endosperm contains starch that is embedded in a
dense protein matrix (Kotarski et al., 1992). The vitreousness of starch in corn kernels increases
as maturity advances and decreases ruminal starch digestibility (Philippeau and Michalet-
Doreau, 1997).
Animal performance
Two continuous studies (20 wk and 4.4 wk, respectively) were conducted to determine how
maturity at harvest of corn silage affects dairy cows in early lactation (Huber et al., 1965; 1968).
In the first study CP and crude fiber concentration tended to decrease and nitrogen-free extract
tended to increase as maturity of corn silage advanced from 25.4 to 33.3% DM (Huber et al.,
1965). Dry matter intake (P < 0.05) and milk production (P < 0.08) increased as DM of the corn
silage increased from 25.4 to 33.3% DM. Milk composition, BW gain, and apparent digestibility
of nutrients were not affected by maturity (Huber et al., 1965). In the second study, ADF and
lignin concentrations decreased as corn silage maturity advanced from 30 to 36% DM, and
increased as maturity advanced from 36 to 44% DM (Huber et al., 1968). Lactic and acetic acid
concentrations declined and ADIN increased as maturity of corn silage advanced from 36 to 44%
DM. Milk production, DMI, and corn silage intake tended to be greatest for cows fed corn silage
harvested at 36% DM compared to cows fed corn silage harvested at 30 and 44% DM (Huber et
al., 1968).
Buck et al. (1969) conducted two trials with primiparous Holstein cows to evaluate the
effect of maturity on intake and milk production. The forage: concentrate ratio of the diet was
approximately 60:40. Corn silage DMI increased as plant maturity increased to approximately
35 g DM/100g. Stage of maturity ranging from 22 to 34% DM (Trial 1) and 32 to 40% DM
(Trial 2) did not alter milk production or digestible energy estimates. In recent studies, the
29
concentrations of NDF, ADF, and CP tended to decline and DM and starch increased with
advancing maturity from milk to BL stages (Hunt et al., 1989; Xu et al., 1995; Harrison et al.,
1996; Bal et al., 1997). In addition, silage pH was lowest and lactate concentration was greatest
with the more immature silages (Bal et al., 1997). However, the relationships between maturity
of corn silage and DMI, milk production, milk component yield, and digestibility of nutrients
were not consistent because when corn silage of varying maturities (early dent: ED to BL) were
fed at approximately 35 to 37% of diet DM, no differences in DMI or milk fat yield were found
(Harrison et al., 1996; Bal et al., 1997). In contrast, milk and milk protein yields were
maximized when corn silage was harvested between ½ and ⅔ ML (Harrison et al., 1996; Bal et
al., 1997). Harvesting corn silage at BL maturity resulted in decreased total tract digestibility of
starch by approximately 5 and 9 percentage units, respectively, when compared with corn silage
harvested at ⅔ ML and 1/2 ML (Harrison et al., 1996; Bal et al., 1997). Forouzmand et al.
(2005) also found that feeding corn silage harvested at BL stage of maturity decreased TMR,
silage and nutrient intake but did not have a major impact on performance of mid-lactation dairy
cows.
Most of these studies suggest that the DM concentration ranges at harvest that optimize the
nutritive value of corn silage and animal performance are between 30 to 39% DM and ½ to ⅔
ML.
Factors Affecting the Fermentation of Corn Silage
Important criteria for the effective preservation of an ensiled crop include a high degree of
lactic acid production and a pH below 4.2 after the fermentation phase (Cleale et al., 1990;
Bolsen et al., 1996). These criteria usually produce silage that is stable under anaerobic
30
conditions. However, several factors affect lactic acid production during silage fermentation
including the following:
Maturity
High DM silage typically has higher pH because the increased osmotic pressure in high
DM silages inhibits the growth of lactic acid bacteria (Woolford, 1984). MacDonald et al. (1991)
suggested that pH tends to increase and organic acids tend to decline as maturity advances
because there is less fermentable substrate available. McDonald et al. (1991) suggested that the
lower pH of less mature corn silage could be related to higher moisture and water soluble
carbohydrate concentrations.
Others also have reported a decline in lactate (Huber et al., 1968; Bal et al., 1997; Johnson
et al., 1997), acetate (Huber et al., 1968; Bal et al., 1997), and ethanol (Bal et al., 1997)
concentration as maturity advanced. However, Johnson et al. (2002) showed that lactate and
acetate concentrations and pH were similar across different maturities of corn silage in two
experiments. In the first experiment, Pioneer hybrid 3845 was harvested at 1) the hard dough
stage, 25.3% DM, 2) ⅓ ML, 28.5% DM, and 3) ⅔ ML, 27.9% DM. In a second experiment at ⅓
ML, 27.1% DM, ⅔ ML, 33.3% DM, and BL, 38 % DM. Ethanol concentration was greatest (P
<0.0001) at the advanced maturity stage (two-thirds ML) in Experiment 1, and greatest (P <0.06)
at the early maturity stage (one-third ML) in Experiment 2.
Foruzmand et al. (2005) studied the effect of maturity of two corn hybrids, Single Cross
704 and Three-Way Cross 647, harvested at ⅓ to ⅔ ML and ⅔ ML to BL respectively, and they
found that pH was less acidic as maturity increased.
Inoculants
Inoculation of forage crops with homofermentative lactic acid bacteria (LAB) can improve
silage fermentation (Muck and Bolsen, 1991) if sufficient fermentable substrate is available
31
(Muck, 1988). Inoculation of grass or legume silage with bacteria has lowered silage pH,
reduced NH3-N, and increased the lactate: acetate ratio in >70% of studies published between
1985 and 1993 (Muck, 1993). Inoculation of corn silage, however, has failed to improve
fermentation quality in many studies (Muck, 1993), and had little effect on final silage pH or
fermentation acids (Bolsen et al., 1980; Cleale et al., 1990), though the rate of pH decline or
production of lactic acid in the first 4 to 7 d of fermentation has been increased in some studies
(Bolsen et al., 1989).
Hunt et al. (1993) studied the effect of two corn hybrids (Pioneer 3377 and 3389) with
similar total plant and grain yield characteristics, ensiled with and without a microbial inoculant
(Pioneer inoculant 1174, Pioneer Hi-Bred International, West Des Moines, IA). They found that
inoculated whole-plant corn silage had lower (3.49 vs. 3.55) pH and tended to have greater
lactate concentrations (6.59 vs. 5.45 % of DM) than non-inoculated silages. The butyrate
concentration was greater (0.08 vs. 0.06% of DM) for inoculated than for non-inoculated corn
silages samples. They concluded that all responses due to their microbial inoculant seemed to be
minor and of little nutritive significance.
Higginbotham et al. (1998) reported that lactic acid of corn silages was not influenced by
inoculants (propionibacteria or propionibacteria with LAB) throughout the fermentation and
storage periods. Acetic acid was not affected; propionic and butyric acid were generally
undetectable. The small difference in concentrations of lactic, acetic, and propionic acids
between the silages from forages inoculated with propionibacteria and the control silage suggests
that the added propionibacteria did not affect normal metabolic activity with respect to
carbohydrates and lactic acid during the ensiling period.
32
Chop Length
Particle size plays a key role in digestion and passage of feed through the gastrointestinal
tract of ruminants and therefore in feed intake. Fernandez and Michalet-Doreau (2002) studied
the fermentation characteristics of four corn silages (Safrane variety, Limagrain Genetics,
Limagne, France) with two chop lengths, namely fine (4.2 mm) and coarse (12.0 mm) harvested
at early stage (24% DM) and late stage (31% DM) of maturity. At the early maturity stage, chop
length had no effect on ensiling fermentation variables. At the late maturity stage, coarsely-
chopped silage was more fermented than the fine silage, resulting in higher lactic acid (52.5 vs.
37.1 g/kg DM) and ethanol (4.7 vs. 1.5 g/kg DM) concentrations, despite the slightly higher DM
concentration.
Fernandez et al. (2004) compared two corn hybrids of whole plant corn silage (WPCS) at
two theoretical chop lengths (TCL), namely fine (5.0 mm) and coarse (13.0 mm). They found
that lactic acid concentration was greater for the coarse WPCS than the fine WPCS, and silage
pH was lower for the coarse WPCS. The pH and lactate concentrations of the coarsely chopped
silage were indicative of desirable silage fermentation.
Processing
Silage fermentation characteristics, DM concentration and DM loss are affected by
mechanical processing (Johnson et al., 1997). Rojas-Bourrillon et al. (1987) reported lower pH
and higher lactate concentration in corn silage processed prior to ensiling. On the other hand,
Cooke and Bernard (2005) reported that pH of kernel processed corn silage tended to be higher
and lactic acid tended to be lower than that of the unprocessed corn silage. Weiss and Wyatt
(2000) also reported greater pH for processed corn silage than unprocessed silage. However,
Dhiman et al. (2000) found similar pH for processed and unprocessed corn silage.
33
Chemical Additives
Britt and Huber (1975) reported that high concentrations of ammonia, but not urea,
depressed lactic acid formation throughout the ensiling period. Kung et al. (2000) studied the
effect of adding ammonia hydroxide to corn plants at ensiling. They found that ammoniation
increased the pH to 9.10 at Day 0, whereas the pH of control silages was 6.52. The lactic acid
concentration was lower in ammoniated silages (0.96% of DM) than in control silages (1.75% of
DM) after 1 d of fermentation, due to a delayed growth of LAB. Concentrations of acetic acid
were greater in ammoniated silages after 0.6, 6 and 60 d of ensiling. In the second experiment,
Kung et al. (2000) studied the effect of adding buffered propionic acid (0.1, 0.2, and 0.3% of
fresh forage) and ammonia-N (0.1, 0.2, and 0.3% of fresh forage) to corn plants at ensiling.
They reported that ammoniated silages had a decreased ratio of lactic: acetic acid and an
increased ammonia-N concentration. However, the effects of the propionic acid-based additive
on silage fermentation were unremarkable.
Factors Affecting Aerobic Stability of Corn Silage
Yeasts
Yeasts are facultative, anaerobic, heterotrophic microorganisms and are considered
undesirable in silages. Silage yeasts ferment sugars to ethanol and CO2 under anaerobic
conditions (Schlegel, 1987; McDonald et al., 1991). This decreases the amount of sugar
available for lactic acid production and the ethanolic silage can taint the flavor of milk (Randby
et al. 1999). Many yeasts species in silages degrade lactic acid to CO2 and H2O under aerobic
conditions, thereby, causing a rise in silage pH, and promoting the growth of other spoilage
organisms (McDonald et al., 1991). Woolford et al. (1982) reported that yeasts are essentially
responsible for the aerobic instability of corn silage. Some authors reported that during the first
weeks of ensiling, yeast populations can increase up to 107colony forming units per gram (cfu/g),
34
though prolonged storage will lead to a gradual decrease in yeast numbers (Jonsson and Pahlow,
1984; Middelhoven and Van Balen, 1988). The presence of oxygen enhances the growth of
yeasts during storage, while high concentrations of formic or acetic acid reduce their growth
(Driehuis and Van Wikselaar, 1996; Oude Elferink et al., 1999). Yeast counts greater than 105
cfu/g are usually indicative of aerobic instability.
Molds and Mycotoxins
Molds are eukaryotic microorganisms that develop in silage when oxygen is present.
Silage infested with mold, is usually easily identified by the large filamentous structures and
colored spores that many species produce. Mold species that have regularly been isolated from
silage belong to the genera Penicillium, Fusarium, Aspergillus, Mucor, Byssochlamys, Absidia,
Arthrinium and Trichoderma (Woolford, 1984; Jonsson et al., 1990; Nout et al., 1993). Molds
cause a reduction in feed value and palatability, and have a negative effect on human and animal
health. Scudamore and Livesey (1998) reported that such mycotoxicoses range from digestive
upsets, fertility problems and reduced immune function, to serious liver or kidney damage and
abortions, depending on the type of and amount of toxin present in the silage. Some important
mycotoxin-producing mold species are Aspergillus fumigatus, Penicillum roqueforti, and
Byssochlamys nivea. P. roqueforti is acid tolerant, it can grow under low oxygen, high CO2
conditions and it is the predominant mold species detected in different types of silages (Lacey,
1989; Nout et al., 1993; Auerbach et al., 1998). A silage that is heavily infested with molds does
not necessarily contain high levels of mycotoxins and not all types of mycotoxins that a mold
specie can produce are always present (Nout et al., 1993). It is possible to have visible molds
without mycotoxins. Therefore, the visible mold-mycotoxin occurrence relationship is not clear.
Mycotoxins are now more frequently associated with crops like corn silage that include
grain and stover fractions. Recently mycotoxins in corn silage have been implicated as the cause
35
of dairy herd health problems during years with near ideal growing conditions and record corn
yields (Rankin and Grau, 2004).
Two species of Aspergillus, Aspergillus flavus and A. fumigatus and/or their mycotoxins,
are reported regularly in silages. Aspergillus flavus is common in hot and dry regions where it
colonizes corn plants in the field and produces aflatoxins and cyclopiazonic acid (Munkvold,
2003). Cyclopiazonic acid (CPA), which is also produced by Penicillium mold, is a potent
specific inhibitor of the endoplasmic reticulum Ca++ - ATPase (Goeger et al., 1988). Aspergillus
fumigatus is a thermotolerant fungus that is regularly isolated from silages. A. fumigatus
produces several different mycotoxins including fumitremogens B and C, and gliotoxin (Cole et
al., 1977).
Aflatoxins are a particular concern in dairy production because they can be passed into the
milk of animals consuming contaminated feed (Masri et al., 1969). Therefore, the Food and
Drug Administration stipulated that the concentration of aflatoxins in US should not exceed 20
ppb in feeds and 0.5 ppb in milk.
Molds within the genus Fusarium produce several classes of significant mycotoxins
including the fumonisins, thichothecenes and zearalenone (D’Mello et al., 1999). Fumonisins
are produced by Fusarium proliferatum and F. verticillioides as well as numerous other related
Fusaria. These two species are extremely common on corn plants and cause ear and stalk rot
diseases (Payne, 1999). In addition, these fungi are able to grow inside the corn plant without
causing disease symptoms (Bacon and Hinton, 1996).
Maintenance of an anaerobic environment in the silo during the fermentation and storage
phases and maintenance of aerobic stability of silage during the feedout phase are important in
silage preservation (Bolsen et al., 1996). Failure to achieve such conditions may cause lower
36
recovery of nutrients, and the production of poor quality silage which can reduce DMI and
animal performance (Chen et al., 1994). Aerobically unstable corn silage and high moisture corn
is defined by heating, mold growth, or mustiness occurring a few cm to several m on the face or
surface of the silo during feedout. Oxygen is the ultimate enemy of the ensiling process because
most molds and yeasts are aerobic and require oxygen for growth. Thus any management
practice that helps exclude oxygen from the silage mass is helpful. Such practices include
harvesting at proper moisture concentrations, rapid filling, adequate packing, and covering with
plastic. This exclusion of oxygen from the silage promotes rapid fermentation by anaerobic
hetero and homofermentative bacteria, thereby reducing the growth of yeasts and molds during
the initial stages of fermentation.
Microbial Inoculants
Higginbotham et al. (1998) examined the effect of microbial inoculants containing
propionibacteria either alone or with Pediococcus cerevisiae and P. cerevisiae plus L. plantarum.
They reported that the addition of microbial inoculants containing propionic acid bacteria did not
affect the fermentation of corn silages; however, silages treated with propionic acid bacteria
tended to heat more slowly and took a slightly longer time to reach their peak temperature. They
concluded that the microbial inoculants evaluated did not prevent detrimental changes in quality
when corn silage was exposed to air. However, propionic acid-based preservatives have been
used to improve the aerobic stability of corn silages because of the antifungal nature of the acid
(Britt et al., 1975; Leaver, 1975). Kung et al. (1998) reported substantial improvements (120 –
160 h) in the aerobic stability of corn silage treated with relatively low concentrations (0.1 to
0.2% of fresh forage weight) of several additives that contained buffered propionic acid as their
primary active ingredient.
37
Lactobacillus buchneri recently has been approved by the Food and Drug Administration
for use as inoculants in grass, corn, legume, and grain silages. This organism has been shown to
dramatically improve aerobic stability of silages by inhibiting the growth of yeasts. The net
result is that silages inoculated with L. buchneri are typically stable when exposed to air. When
applied at the time of ensiling at the rate of 106 cfu per gram of fresh material, L. buchneri has
increased aerobic stability of high moisture corn, corn silage, alfalfa silage, and small-grain
silages relative to untreated controls (Muck, 2001; Taylor and Kung, 2002; Kung et al., 2003;
Kleinschmit et al., 2005). Although the precise mechanism has not yet been determined, the
beneficial impact of L. buchneri appears to be related to the production of acetic acid which
inhibits the growth of yeasts (Driehius, et al., 1999). Yeast and mold counts of L. buchneri
inoculated silages are generally lower at feedout and do not increase as rapidly as in untreated
controls exposed to air (Kung and Ranjit, 2001). As a result, the temperatures of silages
inoculated with L. buchneri tend to remain similar to ambient temperature for several days, even
in warm weather (Taylor et al., 2000). Inoculation with L. buchneri is the most beneficial under
circumstances where problems with aerobic instability are expected. Corn silage, small-grain
silages, and high-moisture corn are more susceptible to spoilage once exposed to air than legume
silages and therefore the latter often respond more favorably to inoculation with L. buchneri
(Muck, 1996).
Ranjit and Kung (2000) reported that silage inoculated with a moderate rate of L. buchneri
(1x105 cfu/g of forage) enhanced the aerobic stability of the corn silage, but the improvement
was small (36 h). However, silage treated with 1x106 cfu/g of L. buchneri of fresh forage had
(900 h) a very extensive heterolactic fermentation that resulted in a marked enhancement in
aerobic stability. Nishino et al. (2004) reported that population of yeasts was lowered to about
38
103 cfu/g when L. buchneri was inoculated, and the stability of corn silage was greatly improved
(48 h). Adesogan et al. (2005) reported that corn silage inoculated with L. buchneri had lower
yeast counts and enhanced aerobic stability by (60.8 h).
Ammonia
Moderate concentrations of ammonia (0.1 to 0.3%) have increased the concentrations of
lactic and acetic acids (Muck and Kung, 1997), decreased proteolysis (Huber et al., 1979; Huber
et al., 1980), improved DM recovery (Goering and Waldo, 1980), and improved the aerobic
stability of corn silage (Britt and Huber, 1975; Soper and Owen, 1977). Many researchers have
suggested that the addition of ammonia to silage improves aerobic stability because of its
fungicidal properties (Depasquale and Montville, 1990). Kung et al. (2000) studied the effect of
ammonia hydroxide (application rate of 0.30% N of fresh forage (35 g DM/100g) weight) on
corn silage. They found that the number of enterobacteria were less than 2.00 log cfu/g after 4 d
of ensiling in control silages but remained high (>5 log cfu/g) in ammoniated silages through 6 d
of ensiling. The persistence of enterobacteria and subsequent growth of heterofermentative LAB
may contribute to higher concentrations of acetic acid in ammoniated silages. The number of
yeasts in control silages increased rapidly; however, the number of yeasts in ammoniated silages
remained low for 144 h after aeration. Alii et al. (1983) reported that numbers of yeasts
decreased immediately in high moisture corn after treatment with ammonia. Britt and Huber
(1975) also reported that ammoniation decreased numbers of fungal colonies in corn silage
within 30 min of initial treatment.
Ammoniation at moderate concentration (lower than 0.7%) decreased yeast and mold
counts in corn silage; however, an undesirable product (4-methylimidazole) is formed under high
concentrations of ammonia (Nishie et al., 1969). Greater concentration of ammonia in silages
could form a reaction with sugars causing bovine bonkers (pupil dilatation, excessive salivation,
39
frequent urination and defecation, convulsions and ataxia). Ammoniation is not widespread in
use because it is expensive, hazardous and corrosive on machinery and humans.
Hemorrhagic Bowel Syndrome
In the last ten years hemorrhagic bowel syndrome (HBS), also known as hemorrhagic
jejunal syndrome (HJS), acute hemorrhagic enteritis, clostridial enterotoxaemia, overeating
disease, and dead or bloody gut disease, has become a syndrome of great concern due to sudden
death of both dairy and beef cattle in the US (Ondarza, 2006). Baker (2002) reported that HBS is
responsible for 2% of the deaths of dairy animals in the US. and the disease seems to be more
prevalent in cooler months (USDA, 2003).
Hemorrhagic Bowel Syndrome is characterized by sudden death of afflicted animals, often
with little or no sign of health problems. Upon autopsy, animals show signs of severe bleeding
in the small intestine. The cause of HBS is unknown; however, some evidence suggests that
there are multiple causes. Several predisposing conditions may need to combine before the
problem occurs (Ondarza, 2006). Analyses of diets, ages of cows, levels of milk production, a
full spectrum of blood chemistry and biochemical assays failed to reveal a consistent clinical
correlation to HBS (Dennison et al., 2002). Cows may show signs of abdominal pain and may
have either constipation or bloody diarrhea. Early postmortem examination of cattle with HBS
shows intestinal lesions with hemorrhages and clots that block the flow of ingested feed. Death
is the result of the obstructed bowel, blood loss, and the resulting anemia.
Researchers have found a positive relationship between rumen acidosis, which facilitates
the passage of more starch to the cow’s intestine, and HBS (Ondarza, 2006). Although many
scientists have found Clostridium perfringens Type A in cows with HBS, Dennison et al. (2002)
reported that it is unclear whether proliferation of C. perfringens is part of the primary disease
process in cows with HBS or occurs as a secondary response. Evidence against C. perfringens
40
playing the primary etiologic role includes the observations that C. perfringens is ubiquitous
(Jensen et al., 1989; Songer, 1996). Furthermore, immunization against Clostridium spp. does
not appear to protect animals from HBS.
Aspergillus fumigatus has been proposed as the pathogenic agent associated with mycotic
HBS in dairy cattle (Puntenney et al., 2003). This group of scientists has associated HBS with
feeding moldy forage or grain due to higher concentrations of Aspergillus fumigatus in the blood
of cows with HBS, though they did not show that moldy feeds directly cause HBS. Earlier work
also suggested that A. fumigatus is a fairly common mold in both hay (Shadmi et al., 1974) and
silage (Cole et al., 1977). Several studies have demonstrated potential for Aspergillus species to
infect the ruminant gut at various sites and to cause enteric hemorrhage. Sheridan (1981)
reported aspergillosis in the calf abomasum. In 1989, Jensen et al (1989) reported that A.
fumigatus infected the terminal gastric compartments, particularly the omasum. Dairy producers
in Florida have had increasing incidences of HBS in their herds and associated this with feeding
of corn hybrids with high SG rankings.
Variable Manure Syndrome
Variable Manure Syndrome (VMS) also appears to be increasing in frequency in dairy
herds particularly in the Southeastern US but occurs sporadically in other regions of the US
(Kelbert, 2004). Variable Manure Syndrome or a drastic swing from normal to loose manure
indicates rumen pH instability and subacute or clinical acidosis. Manure variation from day to
day means the rumen has changed from being a continuous fermenter to a batch fermenter,
which alters the bacterial profile significantly and kills digestive microbes that fuel a healthy
digestive process. VMS leads to poor digestion, undigested feed in the manure, and less than
optimum feed efficiency. Often VMS is found sporadically in a herd on the same day, without
ration changes. The condition is often prevalent after corn is harvested under wet conditions.
41
Three out of the last four corn harvest seasons (2000, 2001, 2002 and 2003) in Florida have been
wet (Kelbert, 2004). During the wet years, silage was typically harvested at below 32% DM and
during the dry years silage was usually harvested above 32% DM. During these wet harvest
years, if the harvest management or rain conditions resulted in a DM below 32% increased
incidence of VMS occurred (Kelbert, 2004). VMS was not seen prior to 1998 when it was
common to harvest corn earlier (<30% DM) rather than later to increase the level of sugars in the
green chop silage. Since SG hybrids have become more widespread at the same time as the
increased incidence of HBS and VMS, some Florida dairymen have believed that these problems
are caused by SG corn hybrids.
Stay-green Corn Hybrids
Stay-green is the general term given to a plant variant in which senescence is delayed
compared with a standard reference genotype. The SG phenotype can arise in one of four
fundamentally distinct ways (Thomas and Smart, 1993). The first two classes are functionally
SG and may occur after alteration of genes involved in the onset of senescence and the regulation
of its rate of progress. However, SG in the remaining two classes is cosmetic, because the plants
are green but lack photosynthetic competence. This may be due to a loss in photosynthetic
capability that normally accompanies senescence combined with maintenance of leaf
chlorophyll, or it may be related to premature death seen in herbarium specimens or frozen foods
that retain greenness because they are rapidly killed at harvest (Thomas and Smart, 1993).
The SG ‘trait’ has been reported in corn (Tollenaar and Daynard, 1978; Ma and Dwyer,
1998; Rajcan and Tollenaar, 1999a, 1999b), and most of the current corn hybrids have some
degrees of SG characteristic. However there is a limited understanding of the physiological
processes underlying the development of this trait in such hybrids. Selection for improved
resistance to disease and reduced leaf senescence at high plant densities (Cavalieri and Smith,
42
1985; Tollenaar, 1991) has led to the introduction of SG cultivars of corn with an extended
period of plant maturation post flowering (Havilah and Kaiser, 1994).
Senescence during kernel filling is related to the quantity of light received by the leaves
and N availability via remobilization to actively growing kernels of maize (Borras et al., 2003).
During senescence, leaves lose their greenness as a result of a decline in chlorophyll
concentration, providing a clear visual symptom of leaf senescence. Delayed appearance of
visual symptoms of leaf senescence or SG has been associated with the improved performance of
more recent corn hybrids in the US (Crosbie, 1982; Tollenaar, 1991; Duvick, 1997).
In sorghum (Sorghum bicolor L.), SG was viewed as a consequence of the balance between
N-demand by the grain and N-supply during grain filling (Borrell et al., 2001). Borrell et al.
(2001) suggested that roots of the SG sorghum maintain greater capacity to extract N from the
soil compared with the non-SG hybrids during kernel filling. Rajcan and Tollenaar (1999) also
suggested that SG corn hybrids have greater N uptake during grain filling than non-SG hybrids.
Ma and Dwyer (1998) found a 20% greater N uptake during grain fill in a SG hybrid than in a
non-SG hybrid, but there were no indications of greater N allocation to the kernels of the SG
corn.
Green leaf area at physiological maturity has proved to be an excellent indicator of SG, and
has been used successfully to select drought-resistant sorghums in the US (Rosenow et al.,
1983). The duration of leaf senescence is a function of the timing of the onset of senescence and
the timing of physiological maturity.
The progress of leaf senescence during the grain-filling period may vary as a result of water
and nitrogen stress (Wolfe et al., 1988; Uhart and Andrade, 1995) and or changes in the source-
to-sink ratio, that is, the ratio between assimilate supply and the potential of the grain to
43
accommodate assimilates (Tollenaar, 1977). Premature leaf death generally occurs in sorghum
when water is limiting during the grain-filling period (Stout and Simpson, 1978; Rosenow and
Clark, 1981).
Rajcan and Tollenaar (1999) proposed that leaf senescence in a recent corn hybrid was
delayed because of an improvement in the ratio of assimilate supply (i.e., source) to assimilate
demand (i.e., sink) during kernel filling. They also found that total N uptake in above ground
portions were 10 and 18% greater in the SG hybrid than an older, non-SG hybrid under low and
high soil N conditions, respectively. However, Sudebi and Ma (2005) reported that three corn
hybrids contrasting in leaf number and stay-greenness grown with a precisely controlled N
supply did not differ in N acquisition, partitioning, and remobilization to different plant parts at
physiological maturity. The SG hybrid remained green at physiological maturity only when there
was an unrestricted N supply, indicating that SG is a trait that is exhibited only under adequate N
availability.
During post-anthesis drought, genotypes possessing the SG trait maintain more
photosynthetically active leaves than those that do not (Rosenow et al., 1983). Differences in
rates of DM accumulation, as well as in radiation-use efficiency, were largest from 3 wk post-
silking to physiological maturity and appeared to be associated with more rapid leaf senescence
in the old hybrids (Tollenaar, 1991; Tollenaar and Aguilera, 1992). Fakorede and Mock (1980)
reported that improved corn hybrids produce more DM because they remain photosynthetically
active during mid-to late grain filling.
Corn silage hybrids with the SG characteristic, grown at relatively high plant populations,
may show improved disease resistance compared with conventional hybrids. This benefit may,
44
however be outweighed by lower whole plant DM in SG cultivars than other cultivars as a result
of their higher proportion of green leaf (Havilah and Kaiser, 1994).
Wilkinson and Hill (2003) examined the benefits of the SG characteristic on crop yield and
DM distribution. They found a lower proportion of ear in SG hybrids than in the conventional
(C) cultivars and noted that this may have limited whole-plant yield by providing less ‘sink’ for
photosynthate as the crop progressed through the later stages of growth. It is notable that yield
of DM was only higher in C cultivars than SG cultivars in the warmest of the four environments,
indicating that environmental effects on yield are likely to be greater than SG effects, particularly
in marginal areas for the growth of forage corn.
Havilah and Kaiser (1994) reported that the SG characteristic reduced the DM
concentration of the corn plant after the crop had reached a milk line score of 2.5 on a scale of 0
(all milk in grain) to 5 (no milk in grain). This 2.5 or half milk line stage is considered to be the
optimal maturity stage for harvesting forage corn for silage (Holland et al., 1990; Havilah and
Kaiser, 1991; Davies and Wilkinson, 1993; Johnson et al., 1999). However, Roth and Lauer
(1997) found a wide range in whole-plant DM concentration (from 280 to 500 g of DM kg-1
fresh weight) and hence maturities at milk line score equivalent to 2.5. The SG characteristic
further invalidates the use of the milk line for predicting harvest dates for corn forage destined
for ensiling.
In situations of relatively low late-season temperatures, without the occurrence of frosts to
kill the leaves, the starch in the endosperm of SG hybrids may become progressively harder with
advancing grain maturity while the stover (leaf and stem) remains too wet for ensiling
(Wilkinson et al., 1998). This can lead to lower grain digestibility and production of significant
amounts of effluent during the ensiling period. Any advantage in crop yield due to the SG
45
characteristic may be offset by increased loss of water-soluble carbohydrates (WSC) as carbon
dioxide during the more extensive fermentation of the wetter crop in the silo (Wilkinson et al.,
1998).
There is very little information in the literature on the influence of the SG characteristic on
the nutritive value of corn silage and the health and performance of dairy cows. Both of the
animal studies in the literature that involved feeding of SG hybrids did not compare such hybrids
to conventional hybrids.
The objectives of this study were the following:
• To determine the optimum maturity stage for harvesting SG corn varieties
destined for silage production, and to determine if there are differences in the
fermentation and aerobic stability of hybrids with contrasting SG rankings.
• To determine the effects of SG ranking, maturity of corn hybrids and simulated
rainfall on the health, feed intake and milk production of dairy cows.
46
CHAPTER 3 EFFECT OF MATURITY AT HARVEST OF CORN HYBRIDS DIFFERING IN STAY-
GREEN RANKING ON THE QUALITY OF CORN SILAGE
Introduction
Corn silage has been used across the US as a source of energy and digestible fiber for dairy
cattle. Florida dairy producers have been concerned about a possible link between reduced milk
yield, digestive upsets and Hemorrhagic Bowel Syndrome in cattle consuming corn silage with
high stay-green (SG) rankings. Such hybrids form the bulk of silage hybrids currently sold in the
US.
Thomas and Smart (1993) characterized a SG trait (i.e., the phenotypes that exhibit delayed
senescence) as having greater water and chlorophyll concentration in the leaves at maturity.
Therefore, high SG rankings are genetically correlated with high stalk and leaf moisture
concentrations (Bekavac et al., 1998). Four classes of SG have been identified by Thomas and
Smart (1993). The first two classes are functionally SG and may occur after alteration of genes
involved in the onset of senescence and the regulation of its rate of progress. However, SG in
the remaining two classes is cosmetic because the plants are green but lack photosynthetic
competence. This may be due to a loss in photosynthetic capability that normally accompanies
senescence combined with maintenance of leaf chlorophyll, or it may be related to premature
death seen in herbarium specimens or frozen foods that retain greenness because they are rapidly
killed at harvest.
Selection for improved resistance to diseases and reduced leaf senescence at high plant
densities led to introduction of corn hybrids with high SG rankings. The SG ranking is assigned
to corn hybrids to reflect greater retention of green leaf, improved health and greater lodging
resistance late in the growing season, typically beyond the black layer stage. The dry-down rates
of the ear and stover of such SG hybrids is asynchronous. The ears mature faster than the stalks
47
and leaves, therefore the leaves remain green and immature while the ear turns brown and the
kernels ripen.
Wiersma et al. (1993) and Coors et al. (1997) demonstrated that corn forage harvested at
immature stages (soft dent) was lower in quality than that harvested between ½ and ¾ kernel
milk line. Such results led to the widely held notion that corn intended for ensiling should be
harvested at the ½ kernel milk line stage to optimize nutritive value. Many modern corn hybrids
released since the research of Wiersma et al. (1993) have the SG characteristic. This trait
maintains the integrity of the plant longer into the fall improving combine-ability. However, the
presence of this characteristic implies that the traditional relationship between whole plant silage
moisture and kernel milk line may no longer hold because it probably results in silages that have
milk lines that are more advanced relative to whole-plant maturity (Bagg, 2001). Therefore,
research is needed to determine the optimal maturity at harvest for optimizing the nutritive value
of corn hybrids with high SG rankings. The objective of this study was to determine the
optimum maturity stage for harvesting corn varieties destined for silage production, and to
determine if there are differences in the nutritive value, fermentation and aerobic stability of
hybrids with contrasting SG rankings.
Materials and Methods
Plot Trial
Planting and establishment. Two varieties of corn with high (HSG) SG rankings (Pioneer
31Y43 (Pioneer Hi-Bred International, Des Moines, Iowa) and Croplan Genetics 827 (Croplan
Genetics, St. Paul, MN) were compared with two varieties with average (ASG) SG rankings
(Pioneer 32D99, Croplan Genetics 799). Each of the four varieties was grown on 2 March, 2004
in four replicated 1 x 6 m plots within each of four blocks at the Plant Science Research and
Education Center, Citra, FL. The relative maturity of the hybrids was 117 + 0.8 d.
48
Fractionation and ensiling. Corn plants within a 1 x 2 m area of each plot were harvested at 25
(Maturity 1), 32 (Maturity 2) and 37 (Maturity 3) g DM/100g on 11 and 26 June and 2 July 2004
respectively. A one-row forage harvester and a cutting height of 20 cm were used at each
harvest. The harvested forage from each plot was weighed and divided into thirds, one third for
for botanical fractionation (ear vs. stover), a second third for chemical analysis and the last third
for ensiling. The ear and stover fractions and the whole plant sample reserved for chemical
analysis were chopped (2 cm) and representatively subsampled (0.2 kg) for DM analysis (105ºC
for 24 h). Representative samples (6.5 kg) of the herbage reserved for ensiling were placed in
polythene bags within quadruplicate 20-L mini-silos (one silo per plot) and sealed. Weights of
the empty and full silos were recorded, and silos were then stored for 107 d at ambient
temperature (25ºC) in a covered barn.
Chemical analysis. Dried whole plant, stover and ear samples were ground to pass through a 1-
mm screen in a Wiley Mill (A. H. Thomas, Philadelphia, PA) and analyzed. Ash concentration
was determined in a muffle furnace at 550ºC for 6 h. Starch was determined using the procedure
of Holm et al. (1986). The anthrone reaction assay (Ministry of Agriculture Fisheries and Food,
1986) was used to quantify water-soluble carbohydrates (WSC). Concentration of total N was
determined by rapid combustion using a macro elemental N analyzer (Hanau, Germany) and
used to compute CP concentrations (CP = N x 6.25). Neutral detergent fiber (NDF) and acid
detergent fiber (ADF) concentrations were determined using an ANKOM Fiber Analyzer
(ANKOM Technology, Macedon, NY) and the method of Van Soest et al. (1991). The in vitro
apparent DM digestibility (IVDMD) was measured using an adaptation of the Tilley and Terry
(1963) procedure for ANKOM Daisy II Incubators (ANKOM Technology, Macedon, NY). The
49
rumen fluid was obtained from two nonlactating, fistulated cows fed a diet consisting of soybean
meal (400 g/day) and bermudagrass hay (Cynodon dactylon) in ad libitum amounts.
For the ensiled forage samples, final silo weights were recorded at silo opening and silages
from each treatment were subsampled for DM determination (450 g), silage juice extraction (20
g), microbial analysis (400 g), chemical analysis (800 g) and aerobic stability (1 kg wet weight).
Samples destined for microbial analyses (yeast and mold counts) were placed in an icebox, and
dispatched the same day to the American Bacteriological and Chemical Research Corporation,
Gainesville, FL. Aerobic stability was measured by placing thermocouple wires at the center of
a bag containing 1 kg of silage within an open-top polystyrene box. The silages were covered
with two layers of cheesecloth to prevent drying. The thermocouple wires were connected to
data loggers (Campbell Scientific Inc., North Logan, UT) that recorded silage and ambient
temperature every 30 min for 5 d. Aerobic stability was denoted by the hours taken for a 2ºC
rise in silage temperature above ambient temperature (23ºC). Silage DM concentration was
determined at 60ºC in a forced air oven for 48 h. Ash concentration was determined in a muffle
furnace at 550ºC for 6 h. Silage juice was obtained by blending 20 g of silage with 200 ml of
distilled water for 30 s at high speed and filtering the slurry through 2 layers of cheesecloth. The
pH was measured at opening and after aerobic stability with a pH meter (Accumet, model HP-
71, Fisher Scientific, Pittsburgh, PA). The filtrate was centrifuged at 4ºC and 21,500 x g for 20
min and the supernatant was frozen (-20ºC) in 20 ml vials for subsequent analysis of volatile
fatty acid (VFA) and ammonia-N (NH3_N). Organic acids were measured using the method of
Muck and Dickerson (1998) and a High Performance Liquid Chromatography (HPLC) system
(Hitachi, FL 7485, Tokyo, Japan) coupled to a UV detector (Spectroflow 757, ABI Analytical
Kratos Division, Ramsey, NJ) set at 210 nm. Ammonia-N was determined using an adaptation
50
for the Technicon auto analyzer (Technicon, Tarrytown, NY) of the Noel and Hambleton (1976)
procedure. Dried silage samples were ground (1-mm screen) and analyzed for WSC, starch, CP,
NDF, ADF, and IVDMD using the same procedures used for dried unensiled plant fractions.
Statistical Analysis
The experimental design was a split plot in which the whole plot was hybrid company x SG
ranking and the subplot was maturity at harvest. The data were analyzed using the GLM
procedure of SAS (SAS Inst., Inc., Cary, NC) and the following model:
Yijkl = µ + Ci + SGj + Mk + Bl + Eijkl
where
μ = overall mean
C = Effect of Company
SG = Effect of Stay-green
M = Effect of Maturity
B = Effect of Block
E = Experimental error
Least squares means and SE were reported. Polynomial contrasts were used to test the
effect of maturity (25, 32 and 37 g DM/100g) on nutritive value and yield. The coefficients for
the contrasts were generated with the IML procedure of SAS. All interactions were examined:
stay-green x maturity, stay-green x company, maturity x company, and stay-green x maturity x
company. Significance was declared at P < 0.05, and tendencies at P < 0.10.
Results and Discussion
All statements about nutritional differences in the hybrids from the two companies relate to
the performance of the hybrids under the test conditions and may not reflect quality differences
51
between other hybrids from these companies, or differences between the tested hybrids under
different growth conditions.
Yield and Chemical Composition of the Unensiled Whole Plant Samples
High SG hybrids had greater DM yield than ASG hybrids at Maturity 1 (17.8 vs. 14.1 t
DM/ha), but this trend was reversed at Maturity 3 (15.6 vs. 20.4 t DM/ha; Table 3-1). Wilkinson
and Hill (2003) found similar yields of conventional and SG corn hybrids harvested at 25.8 to
43.5 g DM/100 g and attributed this to earlier flowering in the conventional hybrids, which
increased the time available for ear development and grain filling between flowering and harvest.
Whole plant DM, ash, starch and CP concentrations were unaffected by SG ranking.
Unlike Croplan Genetics hybrids, Pioneer HSG hybrids had greater DM and starch
concentrations and IVDMD, and lower concentrations of ADF and NDF than their ASG hybrids
(SG x source interaction, P < 0.05). Wilkinson and Hill (2003) reported that whole plant DM
concentration was similar between SG and conventional (C) cultivars. However, Sudebi and Ma
(2005) found that a leafy hybrid had a greater (P < 0.05) whole plant DM concentration than a
SG hybrid. Sudebi and Ma (2005) also found that SG ranking did not affect whole plant CP
concentration at physiological maturity. They reported that SG hybrids do not require more N
than the conventional hybrids to remain green at maturity. This contrasts with previous field
studies in which SG hybrids had greater total N uptake than conventional hybrids (Ma and
Dwyer, 1998; Rajcan and Tollenaar, 1999; Borrell and Hammer, 2000; Borrell et al., 2001).
Neutral and acid detergent fiber concentrations were lower, whereas IVDMD was greater
in Croplan Genetics ASG vs. HSG hybrids. However, Pioneer hybrids had contrasting results
(SG x source interaction, P < 0.05). Nevertheless, IVDMD results for both hybrids reflected
their respective ADF and NDF concentrations.
52
Maturity had a quadratic effect (P < 0.001) on DM yield and IVDMD (P < 0.05), and a
linear effect on yield of digestible DM (P < 0.01), though the rate of change of DM yield and
yield of digestible DM with maturity depended on hybrid source (Maturity x source interaction,
P < 0.01). Whole plant DM and starch concentrations increased linearly (P < 0.001) with
maturity, whereas CP, NDF and ADF concentrations decreased linearly (P < 0.001) at rates that
largely depended on hybrid source (Maturity x source interaction, P < 0.07). These changes
reflect the transition from vegetative to reproductive growth in the plants. Ash concentration
changed quadratically with maturity at rates that differed with hybrid source (Maturity x source
interaction, P = 0.05). Changes in WSC concentration with maturity depended on hybrid source
and SG (SG x maturity x source interaction, P = 0.032). Average SG hybrids had lower yield of
digestible DM than HSG hybrids at Maturity 1 (8.2 vs. 10.1 t of digestible DM/ha), but greater
yields at Maturity 2 (9.0 vs. 8.2 t of digestible DM/ha) and Maturity 3 (11.9 vs. 8.5 t digestible
DM/ha) (SG x Maturity interaction, P < 0.001).
Chemical Composition of the Unensiled Stover Samples
The stover of ASG hybrids had greater (P < 0.05) DM concentrations (Table 3-2) than
HSG hybrids (258 vs. 239 g/kg) though the difference tended to be more pronounced in Croplan
Genetics hybrids (SG x source interaction, P = 0.09). The lower DM concentration of HSG
hybrids agrees with the statement that SG hybrids typically have more moisture in leaves than
conventional hybrids. The results also agree with the work of Sudebi and Ma (2005) who found
that a leafy hybrid had greater (P < 0.05) stover DM concentration than a SG hybrid.
Unlike that of Croplan Genetics hybrids, the stover of Pioneer ASG hybrids had less WSC
than their HSG hybrids (SG x maturity interaction, P = 0.011). The stover of HSG hybrids from
both sources had greater (P < 0.05) CP concentrations than ASG hybrids (86 vs. 74 g/kg of DM),
but the difference tended to be more pronounced for Croplan Genetics hybrids than Pioneer
53
hybrids (SG x maturity interaction, P = 0.068). These results may be due to greater proportion of
chlorophyll in hybrids with higher SG rankings due to greater green leaf proportion. Sudebi and
Ma (2005) also found that a leafy hybrid had lower N concentrations in roots and leaves than SG.
The greater total N accumulation by the SG hybrids was possibly due to the fact that they
remained green after physiological maturity such that they took up N for a longer period of time
than early-senescing hybrids (Sudebi and Ma, 2005; Borrell et al., 2005). Another reason for the
greater CP concentration of HSG hybrids is they exhibit greater retention of chloroplast proteins
than conventional hybrids (Borrell et al., 2001).
Unlike that of Pioneer hybrids, the stover of Croplan Genetics HSG hybrids tended (P =
0.08) to have greater NDF concentration (692 vs. 679 g/kg of DM) and lower (P = 0.08) ADF
concentration (376 vs. 387 g/kg of DM) than that of ASG hybrids, indicating a tendency for
greater hemicellulose concentrations in the stover of HSG hybrids (SG x source interaction, P <
0.05). Therefore, the NDF, ADF and IVDMD results obtained on the stover from each hybrid
source are consistent with those obtained from the corresponding whole plants.
Stover DM increased linearly (P < 0.05), and ash concentration tended to increase linearly
(P = 0.06) with maturity. Concentrations of CP and IVDMD decreased linearly (P < 0.001) with
maturity, whereas concentrations of WSC, NDF and ADF were unaffected. The stover of
Croplan Genetics hybrids had greater (P < 0.05) ash concentration (52 vs. 45 g/kg of DM) and
lower WSC concentration (153 vs. 120 g/kg of DM) than those of Pioneer hybrids.
Chemical Composition of the Unensiled Ear Samples
In agreement with Wilkinson and Hill (2003) and Ettle and Schwarz (2003), ear WSC
concentration decreased linearly (P < 0.001) with increasing maturity, whereas DM
concentration increased linearly (P < 0.001).
54
Unlike Croplan Genetics hybrids, Pioneer HSG hybrids had greater DM and CP
concentrations in the ear than their ASG hybrids (SG x source interaction, P < 0.05; Table 3-3).
High SG hybrids also had greater (P < 0.01) ear ash concentration than ASG hybrids (20 vs. 18
g/kg DM) but ear WSC concentrations were similar among hybrids. The results from the
Pioneer hybrids support those of Ettle and Schwarz (2003) and Wilkinson and Hill (2003) who
noted that SG corn hybrids had greater ear DM concentration than fast dry down and
conventional hybrids, respectively. The CP results contrast with others showing similar N
allocation (Ma and Dwyer, 1998) or N concentration (Sudebi and Ma, 2005) in the kernels of SG
and conventional hybrids.
Chemical Composition of Corn Silage Samples
As reported by Ettle and Schwarz (2003), Croplan Genetics HSG hybrids had lower starch
concentrations than ASG hybrids (Table 3-4). However, a reverse trend was detected among
Pioneer hybrids (SG x source interaction, P < 0.001). Since corn maturation is typically
accompanied by increasing starch deposition (Wilkinson and Phipps, 1979), HSG hybrids should
have greater starch concentration than ASG hybrids. The contrasting trend for the Croplan
Genetics hybrids is partly attributable to fiber concentration differences between hybrids.
Neutral and acid detergent fiber concentrations tended (P = 0.01) to be greater in Croplan
Genetics HSG vs. ASG hybrids, but an opposite trend was evident among Pioneer hybrids (SG x
source interaction, P < 0.001). Consequently, as in the unensiled whole plant and unensiled
stover, the IVDMD of ensiled HSG hybrids from Croplan Genetics tended to be lower than those
of their ASG hybrids, but this trend was not detected among Pioneer hybrids (SG x source
interaction, P = 0.07). Ettle and Schwarz (2003) noted that their dry down variety had greater
(P < 0.05) IVDMD than their SG variety. The lower IVDMD values found in Croplan Genetics
HSG hybrids are probably attributable to their greater NDF and ADF concentrations. The faster
55
rate of ear maturation in such HSG hybrids could have also resulted in more mature, less
digestible kernels. Lower starch and IVDMD in such HSG vs. ASG silages indicates that
nutritive value was lower in the former. This contradicts finding of similar digestibility between
HSG and conventional hybrids by Australian researchers (Havilah and Kaiser, 1994), possibly
due to differences in the prevailing temperature and humidity during the growth of the hybrids.
Kernel processing may be beneficial for improving energy availability from the Croplan
Genetics HSG hybrids.
Water-soluble carbohydrate concentration was greater (P < 0.05) in HSG (7.1 vs. 6.4 g/kg
of DM) than ASG hybrids, and CP concentration tended to be greater (P = 0.08) in HSG than
ASG hybrids (96 vs. 90 g/kg of DM). The latter disagrees with Ettle and Schwarz (2003), who
reported that a fast dry down variety had greater CP concentration than a SG variety. The higher
CP concentration of the HSG hybrids agrees with observations of higher leaf N concentrations in
SG sorghum hybrids (Borrell and Hammer, 2000). This is probably related to greater retention
of chloroplast proteins and greater capacity for N uptake in SG hybrids (Borrell et al., 2001).
Dry matter and starch concentrations increased linearly (P < 0.001) with increasing
maturity, while WSC, CP, NDF and ADF concentrations decreased linearly (P < 0.001), but
maturity did not affect IVDMD. Others have also noted that IVDMD and in situ degradability of
corn silage remained unchanged within the range of maturities examined in this study, and
attributed this to transition from vegetative to reproductive growth (Bal et al., 2000).
Fermentation Indices of Corn Silage Samples
The pH (Table 3-5) of all silages was in the range of 3.71 to 3.81, which reflects good
fermentation. Pioneer HSG hybrids had slightly less acidic pH than their ASG hybrids (3.80 vs.
3.73) but Croplan Genetics HSG hybrids had more acidic pH their ASG hybrids (3.73 vs. 3.77;
SG x source interaction, P = 0.015). Nevertheless, the differences were practically insignificant.
56
The concentrations of NH3-N and most organic acids were similar in HSG and ASG
hybrids and butyric acid was not detected in the silages. Ettle and Schwarz (2003) reported that
dry down and SG varieties had similar pH though the dry down variety had greater (P < 0.01)
lactic acid concentration but lower (P < 0.01) acetic acid concentration than the SG variety.
Silage pH increased linearly (P < 0.01) and ammonia-N concentration changed
quadratically (P < 0.05) with maturity. The pH result agrees with Ettle and Schwarz (2003) and
was partly due to linear (P < 0.001) decreases in concentrations of lactic and acetic acids with
maturity. Changes in NH3N and propionic acid concentration with maturity depended on hybrid
source and SG (SG x maturity x source interaction, P < 0.05). Mold counts were not sufficient
(1 x 105 log cfu/g) to cause spoilage but yeast counts were sufficient to cause rapid deterioration
of the silage. Yeast and mold counts changed with maturity in a manner that depended on hybrid
source and SG (SG x maturity x source interaction, P < 0.01). Nevertheless, aerobic stability
was not affected by maturity because there were sufficient numbers of yeasts to cause rapid
spoilage at all maturities.
Conclusions
Effects of SG ranking on the nutritive value of the hybrids were affected by hybrid source.
In contrast to Croplan Genetics hybrids, Pioneer HSG hybrids had greater ear and whole-plant
DM concentrations than their ASG hybrids; though stover DM concentration was lower in HSG
vs. ASG hybrids from both sources. Unlike Pioneer hybrids, Croplan Genetics HSG hybrids had
greater NDF and ADF concentrations and lower IVDMD in the unensiled whole-plant, the
stover, and the silage than the ASG hybrids, indicating that nutritive value was lower in Croplan
Genetics HSG vs. ASG hybrids. However, silage fermentation and aerobic stability were largely
unaffected by SG ranking of hybrids from both sources. This work therefore suggests that in
some corn hybrids, high SG rankings may be associated with a different moisture distribution
57
and lower nutritive value relative to conventional hybrids. However, effects of SG ranking were
not consistent across the two hybrid sources examined. There was no evidence that the
fermentation and aerobic stability of corn silage was adversely affected by the SG ranking of
corn hybrids.
As the hybrids matured, DM yield, yield of digestible DM, starch, DM concentration, and
yeast counts increased, fiber components, CP and WSC decreased, whereas IVDMD was
unchanged. However, these maturity-related changes differed with hybrid source and SG ranking.
It is concluded that the best combination of DM yield, nutritive value, fermentation quality and
yeast counts were obtained when the corn hybrids were harvested at 32 g DM/100g.
58
Table 3-1. Yield and chemical composition of unensiled whole plants from corn hybrids differing in stay-green (SG) ranking, maturity and source.
P value
Maturity¹ High SG Average SG SE SG Maturity Source2 SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) Yield, 1 17.1 18.4 15.1 13.1 1.5 ns 0.016, Q ns 0.002 ns 0.005 ns (t/ha) 2 15.9 13.8 16.3 12.9 3 13.4 17.7 17.8 22.9 DM, 1 267 220 258 265 18.3 ns <.001, L ns ns 0.05 0.01 ns g/kg 2 306 328 290 352 3 384 348 383 374 Ash, 1 33 32 35 37 2.4 ns 0.009, Q 0.012 ns ns 0.05 ns g/kg DM 2 28 29 28 29 3 29 41 29 34 Starch, 1 175 147 160 206 19.7 ns <.001, L ns ns 0.001 0.001 ns g/kg DM 2 275 276 244 355 3 347 237 279 297 WSC³, 1 91 101 91 127 8.9 0.003 ns ns ns 0.08 0.001 0.032 g/kg DM 2 116 91 136 86 3 84 75 87 130 CP, 1 99 92 95 94 6.7 ns 0.001, L ns ns ns ns ns g/kg DM 2 86 86 82 81 3 83 66 75 79
ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05 ¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN ³ WSC = Water-soluble carbohydrate
59
Table 3-1. Continued P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) NDF, 1 569 608 590 530 18.5 0.002 <.001, L ns ns <.001 0.015 ns g/kg DM 2 463 485 484 392 3 437 561 474 435 ADF, 1 305 318 318 271 15.1 0.008 <.001, L ns ns 0.001 0.065 ns g/kg DM 2 255 249 248 200 3 219 292 245 221 IVDMD, 1 621 592 613 630 17.2 0.004 0.04, Q 0.009 ns <.001 ns ns g/kg DM 2 645 593 641 669 3 652 553 624 625
Yield, 1 10.53 9.59 8.62 7.72 0.6 0.064 0.005, L ns <.001 ns <.001 ns t dig
DM/ha 2 9.53 6.83 10.48 7.6 3 7.94 9.09 10.41 13.51
ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05 ¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN ³ WSC = Water-soluble carbohydrate
60
Table 3-2. Chemical composition of unensiled stovers from corn hybrids differing in stay-green (SG) ranking, maturity and source. P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) DM, 1 235 211 247 249 16.8 0.02 0.012, L ns ns 0.09 ns ns g/kg 2 225 233 235 266 3 270 259 266 284 Ash, 1 42 45 46 49 4.6 0.11 0.06, L 0.024 ns ns ns ns g/kg DM 2 44 44 43 53 3 46 55 49 59 WSC³, 1 124 106 101 158 23.2 ns ns 0.008 ns 0.011 0.006 ns g/kg DM 2 220 77 178 122 3 144 110 151 146 CP, 1 101 99 96 85 9.6 0.02 0.001, L ns ns 0.068 ns ns g/kg DM 2 83 91 77 66 3 67 75 69 49 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN ³ WSC = Water-soluble carbohydrate
61
Table 3-2. Continued P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) NDF, 1 688 692 704 651 19.7 0.08 ns ns ns <.001 ns ns g/kg DM 2 655 715 690 651 3 680 723 690 688 ADF, 1 369 382 399 372 16.5 0.09 ns ns ns 0.005 ns ns g/kg 2 370 393 390 367 3 356 387 396 397 IVDMD, 1 570 552 557 593 22.1 ns <.001, L ns ns 0.002 ns ns g/kg DM 2 573 473 525 546 3 490 464 474 480 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN
62
Table 3-3. Chemical composition of unensiled ears from corn hybrids differing in stay-green (SG) ranking, maturity and source. P value Maturity¹ High SG Average SG SE SG Maturity Source2 SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) DM, 1 318 230 297 306 22.5 0.109 <.001, L ns ns 0.012 0.006 ns g/kg 2 447 449 430 526 3 552 526 547 587 Ash, 1 24 25 25 21 1.1 0.003 <.001, L 0.087 ns ns ns ns g/kg DM 2 18 15 17 16 3 18 20 16 16 WSC³, 1 99 108 116 111 11.4 ns <.001, L ns ns ns ns ns g/kg DM 2 76 73 52 68 3 37 56 39 53 CP, 1 99 64 92 79 7.3 ns ns 0.007 ns 0.017 ns ns g/kg DM 2 96 80 85 93 3 95 79 88 90 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN ³ WSC = Water-soluble carbohydrate
63
Table 3-4. Chemical composition of corn silages made from hybrids differing in stay-green (SG) ranking, maturity and source. P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) DM at 1 267 220 258 265 17.8 ns <.001, L ns ns 0.036 0.013 ns harvest, 2 306 322 290 352 g/kg 3 384 348 383 374 Starch, 1 169 143 153 216 15.5 0.001 <.001, L 0.002 ns <.001 ns ns g/kg DM 2 283 244 264 355 3 320 308 297 373 WSC³, 1 9.7 11.7 10.2 9.9 0.6 0.019 <.001, L ns ns ns ns ns g/kg DM 2 5.5 4.2 5.0 4.4 3 5.6 5.7 3.9 5.0 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN ³ WSC = Water-soluble carbohydrate
64
Table 3-4. Continued P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) CP, 1 111 104 100 98 5.6 0.086 <.001,L ns ns ns ns ns g/kg DM 2 96 90 88 89 3 88 84 81 82 NDF, 1 509 536 544 474 14.8 0.068 <.001, L 0.034 ns <.001 ns ns g/kg DM 2 420 446 449 382 3 424 450 450 370 ADF, 1 292 297 318 257 8.5 0.082 <.001, L 0.002 ns <.001 ns ns g/kg DM 2 219 246 264 196 3 226 252 244 187 IVDMD, 1 610 587 660 627 22.9 0.070 ns ns ns 0.07 ns ns g/kg DM 2 640 610 617 676 3 631 590 605 654
ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05 ¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN
65
Table 3-5. Fermentation indices of corn silages silages made from hybrids differing in stay-green (SG) ranking, maturity and source. P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) 1 3.8 3.7 3.7 3.7 0.03 0.09 0.003, L ns ns 0.015 ns ns pH 2 3.8 3.8 3.7 3.8 3 3.8 3.7 3.8 3.8 NHз-N, 1 142 118 137 152 8.7 ns 0.02, Q 0.114 ns ns ns 0.03 g/kg 2 131 109 108 117 Total N 3 126 122 140 112 Lactic acid, 1 76.5 73.1 63.7 86.5 7.7 ns <.001, L ns ns ns ns ns g/kg DM 2 58.4 46.2 56.5 50.8 3 43.0 47.0 56.8 45.9 Acetic acid, 1 44.9 43.1 39.1 51.2 4.7 ns <.001, L ns ns ns ns ns g/kg DM 2 30.9 24.4 28.3 25.5 3 22.6 24.5 30.9 28.8 Propionic 1 12.6 5.8 7.8 13.4 1.9 ns 0.008, L 0.099 ns ns ns 0.04 acid, 2 11.2 7.7 9.1 7.0 g/kg DM 3 7.4 5.7 8.3 3.1 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN
66
Table 3-5. Continued P value Maturity¹ High SG Average SG SE SG Maturity Source² SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99 CPL799 ( m ) ( c ) Molds, 1 3.27 3.27 3.20 3.39 0.3 ns <.001, L ns ns ns ns 0.008 log cfu/g 2 2.25 2.68 3.23 2.25 3 3.02 2.25 2.25 2.25 Yeasts, 1 4.61 5.88 7.04 6.76 0.4 <.001 0.001, L 0.105 0.03 ns 0.03 0.004 log cfu/g 2 5.97 4.54 7.18 6.66 3 8.12 6.11 7.11 7.68 Aerobic 1 24.5 24.9 24.9 24.3 0.5 ns ns ns ns ns ns ns Stability 2 24.4 25.6 25.1 24.0 (h) 3 24.1 24.1 25.1 25.0 ns = not significant, P > 0.10; L = Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
¹ Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. ² Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN
67
CHAPTER 4 EFFECT OF STAY-GREEN RANKING, MATURITY AND MOISTURE CONCENTRATION
OF CORN SILAGE ON THE HEALTH AND PRODUCTIVITY OF LACTATING DAIRY COWS
Introduction
Silage producers in Georgia and Florida have been concerned that ensiling corn hybrids with
high stay-green (SG) rankings has led to increased incidences of digestive upsets, Variable Manure
Syndrome and Hemorrhagic Bowel Syndrome in their cattle in recent years. These problems may
be partly due to excessive moisture levels in corn plants harvested at previously recommended
maturity stages (⅓ to ⅔ milk line) for optimizing corn yield, nutritive value and dairy cow
performance (Bal et al., 1997; Moss et al., 2001).
The SG characteristic typically occurs in variants with delayed leaf senescence due to
partial or complete inhibition of deconstruction of the photosynthetic apparatus during leaf
senescence. Although the SG phenotype is superficially similar in all crop species and
genotypes, the genetic and physiological basis is diverse. Sorghum genotypes with the SG trait
continue to fill their grain normally under drought (Rosenow and Clark, 1981) and exhibit
increased resistance to charcoal rot (Rosenow, 1984) and lodging (Henzell et al., 1984; Woodfin
et al., 1988). Corn silage hybrids with the SG characteristic, grown at relatively high plant
populations, may show improved disease resistance compared with conventional hybrids. This
benefit may, however, be outweighed by lower whole plant DM in SG cultivars than in
conventional cultivars as a result of their higher proportion of green leaf (Havilah and Kaiser,
1994).
The SG trait is beneficial for grain growers because it confers lodging and disease resistance
on the plant thus facilitating combining. However, this trait presents problems for silage producers
because it causes asynchronous maturity and dry down rates in the ear and the stover. The
68
presence of the characteristic implies that the traditional relationship between whole plant silage
moisture concentration and kernel milk line may no longer be valid, and this may be the reason
why farmers are observing increased seepage from silo when using kernel milk line to predict
when to harvest SG corn destined for silage (Lauer, 1998). The SG characteristic hinders
prediction of corn harvest dates with the kernel milk line because kernels get very mature while
whole plant DM remains under 305 g/kg of DM (Thomas, 2001).
Harvesting forages when they are too wet or too dry makes the silage susceptible to effluent
losses and respiration losses, respectively (Barnett, 1954). Crops ensiled with excess moisture are
often poorly fermented due to proliferation of butyric acid-producing clostridia. Delaying harvests
of SG hybrids to allow the stover to dry can predispose to disease infestation. It is also difficult to
ensile crops with excessive DM concentrations because they are difficult to consolidate adequately
in the silo, and the residual oxygen in the silo hinders the fermentation. There is very little
information in the literature on how the SG characteristic affects the performance of cattle and
whether rainfall at harvest or ensiling increases problems associated with SG hybrids. The aim of
this study was to determine the effects of corn hybrid SG ranking, maturity and water addition at
ensiling on health, feed intake and milk production of dairy cows.
Materials and Methods
Two experiments were carried out at the Dairy Research Unit of the University of Florida
from October to November 2005 to evaluate how the SG ranking of corn hybrids affects the
performance of dairy cows. In the first experiment, 30 lactating Holstein cows in mid-lactation (92
+ 18 days in milk) were allocated randomly to five dietary treatments for two, 28-d periods. Each
period consisted of 14 d for adaptation to a new diet and 14 d for sample collection. Near isogenic
corn hybrids with high SG (Croplan Genetics 691) and low SG (Croplan Genetics 737) ranking
were grown side by side on a 25-acre field at the Dairy Research Unit, University of Florida. Both
69
varieties were planted on 6 April, 2005, harvested on 12 July, 2005 at 26 g DM/100g (Maturity 1)
and packed into 32-ton, 2.4-m wide Ag-Bags with a Versa Bagger (model ID 1012; Versa Corp.,
Astoria, OR). A further treatment involved adding 15 l of water per ton of silage to the high SG
hybrid during packing with a hose pipe to simulate rainfall. The quantity of water added was the
maximum amount possible that allowed normal operation of the bagger. Both hybrids also were
harvested on 19 July, 2005 at 35 g DM/100g (Maturity 2) and packed into Ag-Bags. The forages
were ensiled for 84 d (Maturity 1) and 77 d (Maturity 2) before the bags were opened.
Diets
For both experiments, the TMR contained corn silage, alfalfa hay and concentrate mixed at
35, 10 and 55% of dietary DM respectively (Table 4.1). The dietary treatments evaluated were the
following: 1) Low stay-green hybrid (LSG) harvested at 26 g DM/100g, 2) High stay-green hybrid
(HSG) harvested at 26 g DM/100g, 3) High stay-green hybrid harvested at 35 g DM/100g, 4) Low
stay-green hybrid harvested at 35 g DM/100g, 5) High stay-green hybrid (HSG wet) harvested at
26 g DM/100g and irrigated. Cows were fed individually twice daily (at 0700 and 1330 h), using
Calan gates (American Calan Inc., Northwood, NH). Feed refusals were collected daily at 0600 h.
Cows were trained to use Calan gates for 10 d before the beginning of the trial. Diets were mixed
prior to feeding using 250-kg Calan Data Rangers (American Calan Inc., Northwood, NH).
Sample Collection and Analysis
In Experiment 1, cows were balanced for parity, milk production and days in milk (DIM) and
assigned to each treatment at the beginning of Period 1. At the end of Period 1, cows were
randomly assigned to another treatment such that no cow was on the same treatment as it was in
Period 1 and no treatment in Period 2 had more than 2 cows from the same treatment in Period 1.
Cows were milked thrice daily at 0200, 1000 and 1800 h and milk production (MP) was measured
for the last 14 d of each period. Milk samples were collected from 2 consecutive milkings on 2 d
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during each week in the last 14 d of each period, preserved with potassium dichromate and stored
at 4ºC. Milk samples were analyzed by Southeast Milk lab (Belleview, FL) for concentration of
fat, true protein and SCC using a Bentley 2000 Near Infrared Reflectance Spectrophotometer
(Bentley Instruments Inc., Chaska, MN). Feed efficiency was calculated as kg of milk/kg of DMI.
Body weight was measured for 3 consecutive days after the 1000 h milking at the beginning and
end of each period. Rectal temperature and the number of ruminal contractions in 2 min period
were measured at 1900 h on the last 5 d of each period. Manure was scored using a 1 to 4 scale,
where 1 was dry manure, 2 was normal manure, 3 was loose manure and 4 was diarrhea. Blood
samples (10 ml) were taken using vacutainers (BD Vacutainer. Franklin Lakes, NJ) containing
sodium heparin by caudal arteriovenipuncture on the last day of each period. Samples were
centrifuged at 2500 x g for 20 min and the plasma was frozen at -20ºC. Concentration of plasma
glucose (Glc) was determined using a Technicon Autoanalyzer II (Bran-Luebbe, Elinsford, NY)
and a method modified from Gochman and Schmidz (1972). Blood urea nitrogen was determined
using an autoanalyzer method (Technicon Industrial systems Autoanalyzer II; Industrial method #
339-01; Tarrytown, NY), which is a modification of the carbamido-diacetyl reaction, described by
Coulombe and Favreau (1963). Plasma concentration of BHBA was determined using the
procedure described by Williamson et al. (1962). Chromic oxide (Cr2O3) was used as an external
marker for determination of apparent digestibility. Chromic oxide powder (Fisher Scientific,
Fairlawn, NJ) was weighed into gelatin capsules (Jorgensen Lab. Loveland, CO) and dosed twice
daily with a balling gun (10 g/dose at 0700 and 1900 h) for 10 consecutive d in each experimental
period. Fecal samples (approximately 150 g) were collected during the last 5 d of each period at
the time of dosing. Feces were dried to constant weight at 60ºC in a convection oven, ground to
pass through a 1-mm screen in a Wiley mill and a composite sample was made from all 10 fecal
71
samples per cow per period. Chromium concentration in feces was determined using a Perkin
Elmer 5000 (Wellesley, MA) Atomic Absorption Spectrometer, according to the procedure
described by Williams et al. (1962). Apparent digestibility of DM, CP, ADF, and NDF were
calculated by the marker ratio technique (Schneider and Flatt, 1975).
Two representative samples of the concentrate, each forage and the TMR were collected
during each week of each collection period and composited, sub-sampled and analyzed for CP,
NDF, ADF, water-soluble carbohydrates (WSC) and starch. Concentration of N was determined
by rapid combustion using Macro elemental N analyzer (Elementar, Hanau, Germany). The NDF
and ADF concentrations were determined using an ANKOM Fiber Analyzer (ANKOM
Technology, Macedon, NY). The anthrone reaction assay (Ministry of Agriculture, Fisheries and
Food, 1986) was used to quantify WSC. Each corn silage also was analyzed for aerobic stability
by placing thermocouple wires at the center of a bag containing 1 kg of silage, within an open-top
polystyrene box. The silages were covered with 2 layers of cheesecloth to prevent drying. The
thermocouple wires were connected to data loggers (Campbell Scientific Inc., North Logan, UT)
that recorded the temperature every 30 min for 10 d. Aerobic stability was denoted by the time
taken (h) for a 2ºC rise in silage temperature above ambient temperature (23ºC).
In Experiment 2, 5 ruminally-fistulated lactating cows were used to evaluate the effect of the
dietary treatments on ruminal pH, VFA concentration and ammonia-N concentration, during 3
consecutive 15-d periods. Each period consisted of 14 d of adaptation and 1 d of ruminal fluid
collection. Ruminal fluid was collected (200 ml) by aspiration and filtered through two layers of
cheesecloth at 0, 2, 4, 6, 8, 10 and 12 h after feeding on the last day of each period. The pH was
measured within 20 min collection using a pH meter (Accumet, model HP-71, Fisher Scientific,
Pittsburg, PA). The ruminal fluid was acidified with 3 ml/sample of H2SO4 (50% v/v). Samples
72
were centrifuged at 12,000 x g for 20 min, after which the supernatant was collected and frozen (-
20ºC) in 20-ml vials. Volatile fatty acids were measured using the method of Muck and Dickerson
(1988) and a High Performance Liquid Chromatograph (Hitachi®, FL 7485, Tokyo, Japan)
coupled to a UV Detector (Spectroflow 757, ABI Analytical Kratos Division, Ramsey, NJ) set at
210 nm. The column used was a Bio-Rad Aminex HPX-87H (Bio-Rad Laboratories, Hercules,
CA 9454) column with 0.015M sulfuric acid mobile phase and a flow rate of 0.7 ml/min at 45ºC.
Ammonia N was determined with a Technicon Auto analyzer (Technicon, Tarrytown, NY, USA)
and an adaptation of the Noel and Hambleton (1976) procedure.
Statistical Analysis
Both experiments involved cross-over designs and the data were analyzed with the Proc
Mixed Procedure of SAS (2002). The model used for analyzing the results from Experiment 1
was:
Yijk = µ + Ti + Pj + Ck + Rl + Eijkl
where
µ: general mean
Ti: treatment effect (fixed effect)
Pj: period effect (fixed)
Ck: cow effect (random effect)
Rl: residual effect
Eijkl: experimental error
The model used for analyzing rumen VFA and ammonia-N data in Experiment 2 was
Yijk = µ + Ti + Pj + Hk + Cl + Eijkl
where
µ: general mean
73
Ti: treatment effect (fixed effect)
Pj: period effect (fixed)
Hk: time effect (repeated measurement)
Cl: cow effect (random effect)
Eijkl: experimental error
The covariance structure used was AR (1), and a slice statement was used to detect
differences among treatments at each incubation time. Significance was declared at P < 0.05 and
tendencies at P < 0.15.
The covariance structure used was AR (1), and a slice statement was used to detect
differences among treatments at each incubation time. For both experiments, orthogonal contrasts
were used to examine effects of SG, maturity and moisture addition (HSG vs. HSG (wet) at
Maturity 1). Significance was declared at P < 0.05 and tendencies at P < 0.15.
Results and Discussion
Chemical Composition of Corn Silage
The ingredient and chemical composition of the TMR is shown in Table 4-1. The silages had
similar DM concentration at silo opening (Table 4-2), though LSG silages had numerically higher
values than HSG silages. Starch concentration was greater for HSG than LSG at Maturity 1 but
lower at Maturity 2. Yeast and mold counts were greater and aerobic stability was lower in the
HSG silage vs. the LSG silage at Maturity 1, but not at Maturity 2. Adding moisture to the HSG
hybrid increased yeast and mold counts and decreased CP, NDF and ADF concentrations. These
results suggest that higher SG ranking was associated with more yeast and mold growth and
spoilage when corn was harvested at 26 g DM/100g, or when water addition increased the
moisture concentration of corn harvested at 26 g DM/100g.
74
Voluntary Intake
Dry matter intake was similar across diets (Table 4-3) but intake of starch tended (P = 0.09)
to be lower for cows fed the HSG diet. Adding moisture to the Maturity 1 HSG hybrid resulted in
increased (P = 0.05) starch intake (5.8 vs. 6.7 kg/d) and a tendency for increased CP intake (P =
0.014). Intakes of CP, NDF and ADF were lower (P < 0.05) in cows fed the HSG diet than those
fed the LSG diet, but these differences tended to be more pronounced in the Maturity 1 silage than
the Maturity 2 silage (SG x maturity interaction, P < 0.01). Ettle and Schwarz (2003) found that
corn silage variety had no effect on feed intake, but daily intake of crude fiber was considerably
less (2.7 kg per cow) for a variety with rapid kernel dry down (DD) compared to a SG variety (3.0
kg per cow), possibly due to a lower concentration of fiber in the DD variety.
Intakes of DM (DMI) and starch were not affected by maturity, while intake of NDF and
ADF decreased (P < 0.05) with maturity. Phipps et al. (2000) reported that DMI of dairy cows
was lower when they consumed corn silage harvested at 39% DM compared to 26 or 29% DM.
Forouzmand et al. (2005) reported that intakes of DM, CP, NDF and ADF were lower when silage
had 37.7% DM (Black layer stage; BL) compared to 26.8% DM (⅓ milk line; ML) or 30.5% DM
(⅔ ML). However, Ettle and Schwarz (2003) reported that total DMI and DMI of corn silage
harvested at 30 to 32% DM (16.5 and 10.5 kg of DM per cow, respectively) were lower (P < 0.05)
than the corresponding intakes in corn silage harvested at 38 to 42% DM (17.8 and 11.8 kg of DM
per cow, respectively). Bal et al. (1997) found no differences in DMI in corn silages with DM at
harvest ranging from 30.1 to 42%. These discrepancies in maturity effects on DMI probably
reflect varietal differences in the experimental silages particularly differences in the concentration
and digestibility of NDF.
Cows fed LSG hybrids had greater (P < 0.01) DM, NDF and CP digestibilities than those fed
HSG hybrids, and the difference in NDF digestibility was more pronounced at Maturity 1
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(Maturity x SG interaction, P= 0.03). Starch digestibility was unaffected by SG ranking. Ettle
and Schwarz (2003) reported that their DD variety had greater (P < 0.05) digestibility of OMD
than a SG variety. The poorer DM digestibilities of the HSG hybrids were largely due to lower
digestibility of NDF and CP in HSG hybrids.
Apparent DM and CP digestibilities were not affected by maturity. Bal et al. (1997) reported
that DMD was similar for cows fed corn silage harvested at 30.1, 32.4 and 35.1% DM. Ettle and
Schwarz (2003) also reported that stage of maturity (30 to 32% DM and 38 to 42% DM) did not
affect OM digestibility. Starch digestibility decreased (P < 0.05) with maturity and tended to be
greater in HSG vs. LSG at Maturity 1 though not at Maturity 2 (SG x maturity interaction, P=
0.12). Bal et al. (1997) also reported a decline in starch digestibility with maturity. The decline in
starch digestibility could be related to lower efficiency of postruminal starch digestion or more
whole kernel passage from the rumen of cows fed the more mature silage (Harrison et al., 1996).
Adding moisture to the Maturity 1 HSG hybrid increased (P < 0.05) CP digestibility (62.3 vs.
65.2%), possibly due to provision of adequate moisture for microbial digestion.
Milk Production and Composition
Milk production and the concentration of milk constituents were largely unaffected by SG
ranking. There was a tendency (P = 0.12) for greater milk production in cows fed Maturity 1 vs.
Maturity 2 diets (Table 4-4). Ettle and Schwarz (2003) reported similar milk yields for DD and SG
varieties. Phipps et al. (2000) also reported that cows fed corn silage harvested at 29 to 30% DM
had greater milk yield than cows fed corn silage harvested at 39% DM. Bal et al. (1997) noted
greater (P < 0.07) milk yield when cows were fed corn silage harvested at 35% DM rather than
30% DM (33.4 vs. 32.4 kg/d). The latter study examined a narrower maturity range than that
explored in this study or those of Phipps et al. 2000, possibly due to varietal differences in NDF
digestibility.
76
Cows fed HSG hybrids had lower milk fat concentration (3.5%) than those fed LSG hybrids
(3.8%) when the hybrids were harvested at Maturity 1, but the reverse occurred in hybrids
harvested at Maturity 2 (SG x maturity interaction, P = 0.04). There was a tendency (P = 0.08)
for milk fat yield to decrease with maturity. Johnson et al. (2002) reported that milk fat yield was
lower (P < 0.02) in corn harvested at 38.2% DM compared to that harvested at 27.1 and 33.3%
DM, and milk fat concentration was lower (P < 0.04) for cows fed corn silage of 38.2% DM
compared to those fed silage at 27.1% DM. A similar decline in milk fat concentration with
increasing maturity was reported also by Phipps et al. (2000) and Forouzmand et al. (2005). In
contrast, Bal et al. (1997) reported that milk fat concentration and milk fat production were not
affected by maturity. The maturity-related decreases in milk fat concentration and yield in this
study are not attributable to differences in fiber concentration of the hybrids at the two maturities,
since ADF and NDF concentrations decreased with maturity.
Milk protein and milk protein yield were not affected by maturity. Johnson et al. (1999) also
found that milk protein concentration was not affected by maturity. However, Bal et al. (1997)
reported that milk protein production was greater (P < 0.05) for cows fed corn silage harvested at
35.1% DM than that harvested at 30.1% DM (ED), 32.4% DM (¼ ML) or 42% DM (BL stage).
They suggested that this was due to the higher starch concentration and digestibility of corn silage
harvested at 35.1% DM.
Efficiency of feed conversion into milk tended (P = 0.14) to improve with corn silage
maturity. This agrees with Forouzmand et al. (2005) who reported that cows fed corn silage
harvested at 37.7% DM were more efficient (P < 0.05) than those cows fed corn silage harvested at
26.8 or 30.5% DM. Adding moisture to the HSG hybrid did not affect milk production, milk
constituent yield or concentration or feed efficiency.
77
Body Weight and Plasma Metabolites
Mean BW was unaffected by SG ranking or maturity, but BW gain increased with maturity
of corn plants and it was lower in cows fed LSG vs. HSG diets (Table 4-5). The latter was
probably because cows fed HSG diets partitioned more nutrients to BW gain. Ettle and Schwarz
(2003) also reported that BW was not affected by variety or maturity. Concentrations of plasma
glucose were not affected by SG ranking, but tended to increase (P = 0.09) with maturity. This
increase was in part due to the greater concentration of starch in the more mature hybrid. Plasma
BUN and BHBA concentrations were not affected by SG ranking or maturity.
Rumen Parameters and Health Indices
Rectal temperature was greater in cows fed HSG (P < 0.05) vs. LSG (38.1 vs. 38.0 ºC), but
the values were within the normal physiological range. Ruminal contraction rate and manure score
were not affected by SG ranking but they increased with maturity (Table 4-6). Ruminal pH tended
to slightly increase with maturity (P = 0.09) reflecting the increased ruminal contraction rate with
maturity. Ruminal pH decreased progressively (P < 0.001) after feeding (Figure 4-1) but only fell
below 6 in cows fed the LSG, Maturity 1 diet.
Ruminal NH3-N concentration was lower (P < 0.01) in cows fed LSG hybrids than in cows
fed HSG hybrids, though this tended to be more evident in cows fed Maturity 1 vs. Maturity 2
diets (Figure 4-2) (SG x maturity interaction, P = 0.06). This suggests that there was enhanced
absorption or uptake of ammonia-N by the ruminal microbes on the LSG diet probably due to
greater fermentable metabolizable energy availability. Ruminal NH3-N concentration decreased
with maturity in cows fed HSG hybrids (27.9 vs. 20.9 mg/dl), but was unchanged with maturity in
cows fed LSG hybrids (19.0 vs. 19.1 mg/dl) (SG x maturity interaction, P = 0.06). Adding
moisture to the HSG hybrid reduced (P < 0.05) the concentration of ammonia-N.
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Ruminal concentration of lactic acid was not affected by SG ranking or maturity, but adding
moisture to the Maturity 1 HSG hybrid reduced (P < 0.05) the concentration of lactic acid.
Ruminal concentration of acetic acid (Figure 4-3) was not affected by SG ranking or moisture
addition. However, acetic acid concentrations decreased (P < 0.001) with hybrid maturity, partly
due to decreases in fiber concentration with maturity. Ruminal concentration of propionic acid
(Figure 4-4) decreased with maturity in cows fed LSG hybrids (19.1 vs. 18.3 molar %), but
increased with maturity in cows fed HSG hybrids (18.3 vs. 20.2 molar %) (SG x maturity
interaction, P < 0.001). Adding moisture to the Maturity 1 HSG hybrid increased (P = 0.05) the
concentration of propionic acid reflecting the greater starch intake in cows fed the HSG wet diet.
Ruminal concentration of iso-butyric acid increased with maturity in cows fed LSG hybrids
(3.1 vs. 4.9 molar %), but was similar at both maturities in cows fed HSG hybrids (3.5 vs. 3.7
molar %) (SG x maturity interaction, P < 0.05). Ruminal concentration of butyric acid (Figure 4-
5) decreased with maturity in cows fed LSG hybrids (12.7 vs. 11.1 molar %), but was similar at
both maturities in cows fed HSG hybrids (12.4 vs. 12.4 molar %) (SG x maturity interaction, P <
0.01). Adding moisture to the HSG hybrids tended (P = 0.09) to decrease butyric acid
concentration. Ruminal concentration of iso-valeric and 2-methyl butyric acids were not affected
by SG ranking but the iso-valeric and 2-methyl butyric acids concentrations increased with
maturity in cows fed LSG hybrids (3.8 vs. 5.1 molar %) and not HSG hybrids (4.6 vs. 4.5 molar
%) (SG x maturity interaction, P < 0.05). Cows fed LSG hybrids had greater (P < 0.01) ruminal
concentration of valeric acid than cows fed HSG hybrids. Concentration of valeric acid was not
affected by maturity or moisture addition.
Ruminal fluid acetate: propionate ratio (Figure 4-6) was lower in cows fed LSG hybrids (3.0
vs. 3.2) at Maturity 1 than HSG hybrids, but this ratio was greater in cows fed LSG hybrids (3.1
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vs. 2.6) at Maturity 2 than HSG hybrids (SG x maturity interaction, P < 0.001). This indicates that
the efficiency of rumen fermentation was greater in cows fed LSG hybrids at Maturity 1 but it was
greater in cows fed HSG hybrids at Maturity 2.
Total VFA concentration was lower (P < 0.01) in cows fed HSG hybrids than cows fed LSG
hybrids at both maturities. However, total VFA concentration decreased with maturity in cows fed
LSG hybrids (99.5 vs. 75.2 mM) but cows fed HSG hybrids had similar values at both maturities
(67.6 mM) (SG x maturity interaction, P < 0.05). Adding moisture to Maturity 1 HSG hybrids
increased (P < 0.001) total VFA concentration which indicates that the extent of fermentation was
increased by this treatment (Figure 4-7). This may have resulted from the greater CP and starch
intake and CP digestibility that occurred when moisture was added to the Maturity 1 HSG diet.
Apparent digestibility is often proportional to ruminal total VFA concentration. The disparity
between these measures in this study may reflect greater post ruminal digestion of the HSG(wet)
diet.
Conclusions
This study shows that the effect of maturity on several performance attributes of the cows
was influenced by the SG ranking of the hybrids. Nevertheless, harvesting corn silage at 35
instead of 26 g DM/100g tended to decrease milk yield and milk fat yield, but increased manure
score, rumen contractions and BW gain, and tended to increase rumen pH, plasma glucose
concentration and the efficiency of feed utilization for milk production. This suggests that corn
silage should be harvested at 35 instead of 26 g DM/100g to optimize rumen health and improve
the efficiency of feed conversion into milk.
Feeding a hybrid that had a higher SG ranking resulted in lower apparent DM and CP
digestibilities, greater BW gain, greater though physiologically normal rectal temperature; but did
not adversely affect other health measures or milk production by the cows. No incidence of
80
digestive upset, diarrhea or Hemorrhagic Bowel Syndrome occurred in the cows. Therefore no
direct link between high SG rankings in corn silages and the incidence of these problems was
found in this study.
Addition of moisture to HSG hybrids to simulate rainfall at harvest increased CP and starch
intake, CP digestibility and total VFA concentrations in ruminal fluid. However, moisture addition
was also associated with greater numbers of yeasts and molds decreased aerobic stability
indicating the importance of harvesting and ensiling corn under dry conditions.
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Table 4-1. Ingredient and chemical composition of the diets
Ingredient g/100g of DM Corn silage 35.0 Alfalfa hay 10.0 Cottonseed meal 4.4 Citrus pulp 4.8 Cottonseed hulls 4.7 Soy Plus 4.2 Corn meal 17.3 Soybean meal 4.2 Whole cottonseed 9.2 Molasses 2.8 Mineral mix¹ 3.4
Chemical composition
Maturity at harvest Maturity 1 Maturity 2 SE LSG2 HSG3 HSG(wet)4 LSG2 HSG3 DM, g/100g 51.5 51.0 50.0 59.7 59.7 0.14 Starch, g/100g of DM 22.5 23.1 24.0 24.9 24.0 0.09 CP, g/100g of DM 18.7 18.7 18.6 18.5 18.6 0.01 NDF, g/100g of DM 32.2 31.9 30.8 30.3 30.7 0.09 ADF, g/100g of DM 21.1 21.2 20.4 19.9 20.1 0.07
1 Mineral mix contained 24.75% CP, 9.9% Ca, 1.1% P, 7.15% K, 2.75% Mg, 8.25% Na, 1448 mg/kg of Mn, 445 mg/kg of Cu, 1552 mg/kg of Zn, 8.54 mg/kg of Se, and 15.5 mg/kg of I. 147,756 IU of vitamin A/kg, and 717 IU of vitamin E/kg (DM basis).
Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest
2 LSG = Low stay-green hybrid 3 HSG = High stay-green hybrid 4 HSG (wet) = HSG hybrid wetted with 15 L of water/ton of forage at ensiling
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Table 4-2. Chemical composition of corn silages differing in maturity, SG ranking and moisture treatment at ensiling (n=4) Maturity 1 Maturity 2 SE LSG1 HSG2 HSG(wet)3 LSG1 HSG2 DM at silo opening, g/kg 303 289 295 353 350 5.7 Ash, g/kg DM 41 39 33 35 38 0.9 Starch, g/kg DM 291 332 333 360 333 2.6 WSC4, g/kg DM 9.5 9.5 9.8 9.8 9.5 0.1 CP, g/kg DM 89 90 87 85 84 0.3 NDF, g/kg DM 458 449 400 392 411 6.8 ADF, g/kg DM 271 275 243 226 243 3.7 Yeast, log cfu5/g 1.00 3.38 6.11 4.83 4.58 0.5 Mold, log cfu5/g 1.45 2.45 6.30 5.92 5.09 0.3 Aerobic stability6, h 18.3 7.3 6.8 7.3 6.5 0.8
Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest 1 LSG = Low stay-green hybrid 2 HSG = High stay-green hybrid 3 HSG (wet) = HSG hybrid wetted with 15 l of water/ton of forage at ensiling. 4 WSC = Water soluble carbohydrate 5 cfu = colony forming units 6 Aerobic stability = Number of hours that elapsed before silage temperature exceeded ambient temperature by > 2ºC.
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Table 4-3. Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on feed intake and digestibility of lactating dairy cows.
Maturity 1 Maturity 2 SE Effects (P value) LSG1 HSG2 HSG(wet)3 LSG1 HSG2 SG MAT SG*MAT MOISTIntake, kg/d DM 29.8 26.3 27.3 26.7 26.1 1.4 ns ns ns ns Starch 6.6 5.8 6.7 6.5 6.2 0.3 0.09 ns ns 0.05 CP 5.6 4.7 5.1 4.9 4.8 0.2 0.02 0.080 0.07 0.14 NDF 9.6 8.0 8.4 8.0 7.9 0.4 0.04 0.011 0.05 ns ADF 6.3 5.3 5.6 5.3 5.1 0.3 0.02 0.004 0.05 ns Digestibility, g/100g DM 68.4 61.6 63.9 68.4 64.7 1.2 0.001 ns ns ns NDF 60.1 49.2 47.0 54.6 50.7 1.8 0.001 0.12 0.03 ns CP 69.1 62.3 65.2 68.7 64.3 1.1 <.001 ns ns 0.03 Starch 98.1 98.5 98.4 97.9 97.8 0.2 ns 0.01 0.12 ns
Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest ns = not significant, P > 0.15 1 LSG = Low stay-green hybrid 2 HSG = High stay-green hybrid 3 HSG (wet) = HSG hybrid wetted with 15 l of water/ton of forage at ensiling
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Table 4-4. Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on milk production and composition from lactating dairy cows.
Maturity 1 Maturity 2 SE Effects (P value) LSG1 HSG2 HSG(wet)3 LSG1 HSG2 SG MAT SG*MAT MOISTMilk, kg/d 36.9 37.5 37.5 36.2 36.3 1.3 ns 0.12 ns ns Milk fat, g /100g 3.79 3.49 3.71 3.33 3.54 0.1 ns 0.08 0.04 ns Milk protein, g/100g 2.93 2.91 2.90 2.95 2.90 0.0 ns ns ns ns Milk fat, kg/d 1.40 1.33 1.33 1.28 1.28 0.1 ns 0.09 ns ns Milk protein, kg/d 1.08 1.12 1.09 1.08 1.09 0.0 ns ns ns ns SCC, 10³ cells/ml 578 634 477 567 347 197 ns ns ns ns Feed efficiency, kg milk/kg DMI 1.25 1.38 1.40 1.39 1.42 0.1 ns 0.14 ns ns Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest ns = not significant, P > 0.15
1 LSG = Low stay-green hybrid 2 HSG = High stay-green hybrid 3 HSG (wet) = HSG hybrid wetted with 15 l of water/ton of forage at ensiling
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Table 4-5. Effect of maturity and moisture addition to corn silages with contrasting stay-green (SG) rankings on body weight and plasma metabolites in lactating dairy cows.
Maturity 1 Maturity 2 SE Effects (P value) LSG1 HSG2 HSG(wet)3 LSG1 HSG2 SG MAT SG*MAT MOISTBW, kg 628 638 638 634 636 14.0 ns ns ns ns BW gain, kg/d 0.30 0.61 0.74 0.62 0.80 0.11 0.03 0.03 ns ns Plasma BUN, mg/dl 19.4 19.4 19.1 18.8 19.7 0.8 ns ns ns ns Plasma glucose, mg/dl 64.4 66.1 66.6 66.9 66.9 1.0 ns 0.09 ns ns β-Hydroxybutyrate, mmol/l 0.25 0.29 0.29 0.27 0.26 0.03 ns ns ns ns
Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest ns = not significant, P > 0.15
1 LSG = Low stay-green hybrid 2 HSG = High stay-green hybrid 3 HSG (wet) = HSG hybrid wetted with 15 l of water/ ton of forage at ensiling
86
Table 4-6. Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on rumen parameters and health indices of lactating dairy cows.
Maturity 1 Maturity 2 SE Effects (P value) LSG1 HSG2 HSG(wet)3 LSG1 HSG2 SG MAT SG*MAT MOISTRectal temperature, ºC 38.06 38.11 38.00 37.89 38.17 0.1 0.03 ns ns ns Rumen contractions, /min 2.21 2.22 2.14 2.44 2.41 0.1 ns 0.12 ns ns Manure score4 2.48 2.53 2.68 2.72 2.63 0.14 ns 0.03 ns ns pH 5.9 6.0 6.1 6.1 6.0 0.1 ns 0.09 ns ns NHз-N, mg/dl 19.0 27.9 21.6 19.1 20.9 2.0 0.008 0.08 0.06 0.03 Lactic acid, molar % 1.7 1.9 0.4 1.1 1.9 0.5 ns ns ns 0.02 Acetic acid, molar % 58.1 57.8 57.6 55.8 54.1 0.6 ns <.001 ns ns Propionic acid, molar % 19.1 18.3 19.2 18.3 20.2 1.2 0.09 0.12 <.001 0.05 Iso Butyric acid, molar % 3.1 3.5 3.2 4.9 3.7 0.4 0.14 0.002 0.014 ns Butyric acid, molar % 12.7 12.4 11.9 11.1 12.4 0.6 0.01 0.001 0.001 0.09 Iso Valeric acid and 2-methyl butyric acids, molar % 3.8 4.6 4.5 5.1 4.5 0.7 ns 0.03 0.014 ns Valeric acid, molar % 2.6 2.2 2.5 2.5 2.0 0.3 0.003 ns ns ns Acetate: Propionate 3.0 3.2 3.0 3.1 2.6 0.1 <.001 <.001 <.001 0.04 Total VFA, mM 99.5 67.6 112.4 75.2 67.2 5.7 0.001 0.03 0.04 <.001
Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest ns = not significant, P > 0.15
1 LSG = Low stay-green hybrid 2 HSG = High stay-green hybrid 3 HSG (wet) = HSG hybrid wetted with 15 l of water/ton of forage at ensiling
4 Manure was scored on a scale of 1 to 4; 1 = dry, 2 = normal, 3 = loose, 4 = diarrhea
87
5
5.5
6
6.5
7
0 2 4 6 8 10 12
Time after feeding, h
pH
LSG Mat 1HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-1. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal fluid pH. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water/ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
88
0
6
12
18
24
30
36
42
48
0 2 4 6 8 10 12
Time after feeding, h
NH
3-N
, mg/
dl
LSG Mat 1
HSG Mat 1
HSG Mat 2
LSG Mat 2
HSG(wet) Mat 1
Figure 4-2. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal NH3-N concentration. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water/ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
89
48
50
52
54
56
58
60
62
0 2 4 6 8 10 12
Time after feeding, h
Ace
tic a
cid,
mol
ar % LSG Mat 1
HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-3. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal acetic acid molar percentage. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water /ton of forage at ensiling/ton, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
90
14
16
18
20
22
24
0 2 4 6 8 10 12
Time after feeding, h
Prop
ioni
c ac
id, m
olar
%
LSG Mat 1HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-4. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal propionic acid molar percentage. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water /ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
91
9
10
11
12
13
14
0 2 4 6 8 10 12
Time after feeding, h
But
yric
aci
d, m
olar
%
LSG Mat 1HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-5. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal butyric acid molar percentage. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water/ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
92
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
0 2 4 6 8 10 12
Time after feeding, h
C2:
C3
ratio
LSG Mat 1HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-6. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal acetic: propionic acid ratio. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water/ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
93
40
60
80
100
120
140
160
180
0 2 4 6 8 10 12
Time after feeding, h
Tota
l VFA
, mM LSG Mat 1
HSG Mat 1HSG Mat 2LSG Mat 2HSG(wet) Mat 1
Figure 4-7. Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on ruminal total VFA concentration. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (wet) = HSG wetted with 15 L of water/ton of forage at ensiling, Mat 1 = 26 g DM/100g at harvest, Mat 2 = 35 g DM/100g at harvest.
94
CHAPTER 5 GENERAL SUMMARY
A series of studies were conducted to determine the maturity at which the nutritive value of
stay-green (SG) corn hybrids is optimized and to investigate whether corn hybrids with high SG
rankings cause Variable Manure Syndrome (VMS) and Hemorrhagic Bowel Syndrome (HBS) in
dairy cows. The SG characteristic is desirable for corn grain production because it confers
resistance to lodging and disease infestation to corn plants. However, this characteristic is
undesirable for silage producers because it results in asynchronous drying rates in the ear and
stover, which may invalidate the use of the milk line for accurate prediction of harvest dates.
Several dairy producers in Florida have associated increased incidence of HBS in their cows in
recent years with intake of SG corn hybrids. Therefore there is a need for research into optimal
maturity at harvest of such hybrids and the existence of a link between HBS and SG corn intake.
The objective of Experiment 1 was to determine the optimum maturity stage for harvesting
SG corn varieties for silage production, and to determine if there are differences in the
fermentation and aerobic stability of hybrids with contrasting SG rankings. Two varieties of corn
with high (HSG) SG rankings (Pioneer 31Y43, Croplan Genetics 827) were compared with two
varieties with average (ASG) stay-green rankings (Pioneer 32D99, Croplan Genetics 799). These
varieties were grown on 1 x 6 m plots and harvested at 25 (Maturity 1), 32 (Maturity 2) and 37
(Maturity 3) g DM/100g. The harvested forage was divided into three portions, one each for
botanical fractionation (ear vs. stover), whole plant chemical analysis and ensiling. Representative
samples (6.5 kg) of the herbage reserved for ensiling were placed in polythene bags in
quadruplicate within 20-l mini silos and sealed. Silos were stored for at least 107 d at ambient
temperature (25ºC) in a covered barn.
95
The stover of ASG hybrids had greater DM concentrations and lower CP concentrations than
those of HSG hybrids from both sources, though these differences tended to be more pronounced
in Croplan Genetics hybrids. These results reflect the greater green leaf and stem proportion in
HSG hybrids. Unlike those of Pioneer hybrids, the stover, whole plant and silage from Croplan
Genetics HSG hybrids had greater NDF and ADF concentrations and lower starch concentration
and IVDMD than the corresponding ASG hybrids. Thus, the higher SG ranking was associated
with poorer nutritive value in Croplan Genetics hybrids. Therefore this study indicates that
hybrids from different companies may have different nutritional attributes. The SG attribute may
affect the moisture distribution of some corn hybrids, whereas it affects the nutritive value of
others. However, the fermentation and aerobic stability of ASG and HSG hybrids were largely
similar, therefore the SG attribute did not adversely affect silage quality in this study.
As the hybrids matured, DM yield, yield of digestible DM, starch, DM concentration, and
yeast counts increased, whereas fiber components, CP and WSC decreased, consequently IVDMD
was unchanged. However, the nature of these maturity-related changes differed with hybrid source
and SG ranking. It is concluded that the best combination of DM yield, nutritive value,
fermentation quality and yeast counts was obtained when the corn hybrids were harvested at 32 g
DM/100g.
The objective of Experiment 2 was to determine the effects of SG ranking, maturity and
simulated rainfall on the quality of corn silage and health, feed intake and milk production of dairy
cows. The near isogenic hybrids used were Croplan Genetics 691 (high stay-green, HSG) and
Croplan Genetics 737 (low stay-green, LSG). The hybrids were harvested at 26 g DM/100g
(Maturity 1) and 35 g DM/100g (Maturity 2) and packed into 2.4-m wide, 32-ton Ag-Bags. A
further treatment involved adding 15 l of water per ton of silage to forage harvested at Maturity 1
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to simulate rainfall at harvest. The water was added with a hosepipe during packing. Thirty
lactating Holstein cows in mid-lactation (92 days in milk (DIM)) were allocated randomly to the
five silages for two, 28-d periods. The silages formed part of a TMR consisting of corn silage,
alfalfa hay and concentrate mixed at 35, 10 and 55 g/100g (DM basis) respectively. Dry matter
intake, digestibility, milk production and composition, blood and ruminal function parameters
were measured.
Intake of starch, CP, NDF and ADF were lower in cows fed HSG vs. LSG hybrids, though
the differences in CP and fiber intakes were more pronounced in cows fed Maturity 1 vs. Maturity
2 diets. The digestibilities of DM, NDF and CP were also lower in cows fed HSG vs. LSG hybrids,
though the difference in NDF digestibility was more pronounced at Maturity 1. Cows fed HSG
diets also had greater rectal temperature and BW gain. However, milk production and the
concentration of milk constituents were largely unaffected by SG ranking. These results suggest
that the higher SG ranking was associated with lower feed digestibility and intake but it did not
adversely affect the health of the cows.
Milk production tended to be greater in cows fed Maturity 1 vs. Maturity 2 diets. Cows fed
HSG hybrids had lower milk fat concentration than those fed LSG hybrids harvested at Maturity 1,
but the reverse occurred in hybrids harvested at Maturity 2. There was a tendency for milk fat
yield to decrease with maturity. Milk protein concentration and yield were not affected by
maturity. However, manure score, rumen contractions BW gain, ruminal pH, plasma glucose
concentration and the efficiency of feed conversion into milk improved or tended to improve with
corn silage maturity. This suggests that corn silage should be harvested at 35 instead of 26 g
DM/100g to optimize rumen health and improve the efficiency of feed conversion into milk.
97
Adding water to the Maturity 1, HSG hybrid reduced ruminal ammonia-N concentration but
increased starch intake, CP digestibility and ruminal VFA concentration, and tended to increase CP
intake. This suggests that water addition improved dietary protein and energy utilization, probably
because the added water provided more conducive conditions for enzymatic nutrient hydrolysis.
However water addition was associated with greater yeast and mold counts and poorer silage
aerobic stability, reflecting the importance of harvesting and ensiling corn silage under dry
conditions.
These experiments did not demonstrate a direct link between HSG corn hybrids and VMS
and HBS. Indeed several researchers now consider HBS to be caused by multiple factors
including bad silage management practices such as inadequate packing, harvesting or ensiling
while it is raining, harvesting crops too early or feeding excess levels of readily fermentable
carbohydrates, etc. Although this work has not shown a direct link between HBS and SG, it
confirms the finding that higher SG rankings are associated with poorer nutritive values in hybrids
from Croplan Genetics.
More work is needed to investigate the causes of HBS in dairy cows and the role of SG
hybrids in the etiology of the disease. Such studies should:
(i) Compare SG hybrids to traditional non-SG hybrids.
(ii) Examine diurnal fluctuations in body temperature of cows fed such diets.
(iii) Monitor levels of indices of the immune status of the cows.
(iv) Examine the existence of an interaction between dietary concentrate level, SG ranking
and moisture at ensiling.
(v) Sample silages and blood samples for A. fumigatus and C. perfringens counts.
98
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BIOGRAPHICAL SKETCH
Kathy Gisela Arriola was born on September 18, 1973, in San Francisco, California. The
youngest of four children, she grew up mostly in Lima, Peru. She graduated with honors from
Liceo Naval Teniente Clavero High School in 1990 and she earned her B.S. in animal science
from the Universidad Nacional Agraria La Molina, Peru in 1998. While at the Agraria La
Molina she earned pre-professional experience in the Investigation Program for swine, beef
and dairy cattle. After working for one year as a consultant for dairy farmers, she moved to
Florida in 2000 and worked. In 2004, Kathy was accepted into the M.S. program in the
Department of Animal Sciences at the University of Florida (UF) under the guidance of Dr.
Adegbola Adesogan. While pursuing her M.S. in ruminant nutrition she was given the
opportunity to assist in several projects related to her field. Kathy was involved in the Animal
Science Graduate Student Association and she was an active member of Gamma Sigma Delta.