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Effect of Stay-Green Ranking, Maturity, and Moisture Concentration of Corn Hybrids on Silage Quality and the Health and ...

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 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Literature review
 Effect of maturity at harvest of...
 Effect of stay-green ranking, maturity...
 General summary
 References
 Biographical sketch
 

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1 EFFECT OF STAY-GREEN RANKING, MATU RITY AND MOISTURE CONCENTRATION OF CORN HYBRIDS ON SI LAGE 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 FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

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2 Copyright 2006 by Kathy Gisela Arriola

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3 To my adorable son Wilhelm Andre.

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4 ACKNOWLEDGMENTS I would like to thank my supervisory co mmittee 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. pr ogram. 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 Hu isden, Dervin Dean, Nathan Krueger, SamChurl Kim, Jamie Foster, Susan Chikagwa-Malun ga, Mustapha Salawu, Tolu Ososanya, Sergei Sennikov and Ashley Hughes) for their help durin g 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 importa nt 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 la boratory and field. Finally, I thank my son, Wilhelm Andre, who has been my daily inspiration.

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5 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 Nutri tive Value of Corn Plants............................................................13 Hybrid......................................................................................................................... .....13 Brown midrib hybrids..............................................................................................14 Grain digestibility (flin t vs. dent hybrids)................................................................14 High-oil hybrids.......................................................................................................17 High-grain yield a nd 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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6 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 th e 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 RANKI NG, 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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7 LIST OF TABLES Table page 3-1 Yield and chemical composition of un ensiled whole plants from corn hybrids differing in stay-green (SG) ra nking, 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 co rn silages silages made from hybrids differing in staygreen (SG) ranking, maturity and source...........................................................................65 4-1 Ingredient and chemical composition of the diets.............................................................81 4-2 Chemical composition of corn silages di ffering 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 a nd 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 producti on 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 me tabolites 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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8 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 prop ionic acid molar percentage.....................................90 4-5 Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green rankings on ruminal but yric 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 rumina l total VFA concentration..................................................93

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9 Abstract of Thesis Presen ted 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, MATU RITY AND MOISTURE CONCENTRATION OF CORN HYBRIDS ON SI LAGE 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 nu tritive value of corn (Zea mays L .) hybrids with contrasting (stay-green) SG rankings and the performance of dairy cattle. Experiment 1 determined how maturity a ffects dry matter (DM) yiel d, 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 pl ant chemical analysis, and ensiling. The latter was ensiled (15 kg) in quadruplicate in 20-L mini-s ilos 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 di d not affect silage fermenta tion 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 dair y 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 (Matur ity 2) and ensiled in 32-ton plastic bags for at least 77 d.

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10 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 si lage, 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. Harves ting corn silage at 35 instead of 26 g DM/100g increased the efficiency of feed utilization fo r milk production but decreased or tended to decrease intakes of CP and NDF, apparent diges tibility 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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11 CHAPTER 1 INTRODUCTION Several dairy producers in Florida have experi enced considerable losses in milk production in the past few years due to Variable Manur e Syndrome and Hemorrhagic Bowel Syndrome. Many producers believe that these problems are cause d by corn silage with high stay-green (SG) ranking. Stay-green hybrids have asynchronous ear and st alk dry down rates, th erefore their ears turn brown and their kernels dry down and mature fa ster 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 wate r and chlorophyll concentration in the leaves at maturity. Therefore, high SG rankings are genetically co rrelated with high stal k and leaf moisture concentrations (Bekavac et al., 1998). The pres ence 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 harv esting 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, respectivel y (Barnett, 1954). Crops ensiled with excess moisture are often poorly fermented due to prolifera tion of butyric acid-producing clostr idia. It is also difficult to ensile crops with excessive DM concentrations becau se 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 re adily available commercially because most current hybrids have the SG phenot ype. 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 no t determine how the SG

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12 ranking affects the ideal maturity at harvest of corn silage. Therefore, there is a need to determine the ideal maturity stage for harv esting SG corn hybrids that are wi dely used for silage production. The aim of this study was to determine the effect of maturity at harvest on th e nutritive value of the corn silage hybrids with contra sting SG rankings, and to determin e the effect of feeding corn silages differing in SG ranking, maturity and mois ture concentration on the performance of dairy cattle.

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13 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 concen trations 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 matte r 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 resi stance and drought tolerance. However these measurements alone are poor indicators of nutritive value (Cox and Cherney, 2001). More recent criteria utilized for hybrid selection incl ude fiber and starch digestibi lity in order to maximize milk production per hectare or milk pr oduction per ton of silage (Hunt et al., 1993; Barriere et al., 1995). In selection of corn hybrids, more emphasi s has been placed on grain production than silage production. Grain producers have been reluctant to select hybr ids based on nutritional quality because this attracts re latively little economic value. Ye t hybrid selection for agronomic potential and nutritive value is one of the most important management deci sions influencing corn silage production and subsequent m ilk yields (Allen et al., 1997). Xu et al. (1995) reported that corn silage hybrid and maturity affected the DM concentration of vari ous plant parts including leaves, ear, husk, stalk and stover. Johnson et al. (2001) harveste d 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 starc h, non fiber carbohydrates (NFC), and crude protein (CP) than

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14 Quanta. Some current areas of focus in hybrid sel ection that have nutritional implications will be discussed in the following paragraphs. Brown midrib hybrids The recent focus of most of the genetic improve ment of corn silage has been on enhancing fiber digestibility in order to increase DM inta ke (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 y ears after their initial discovery, BMR mutations were found to have a major effect on lignin conc entration (Lechtenberg et al., 1972) leading to improved digestibility of corn si lage by ruminants. Brown midrib hybrids contain less lignin in the stalks and leaves than normal hybrids, resulting in greater stover digestib ility and in vitro true digestibility (IVTD) (Lecht enberg 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 (Frenchi ck et al., 1976; Miller and G eadelman, 1983; Cherney et al., 1991; Allen et al., 1997), and had increased susceptibility to l odging (Cherney et al., 1991). Feeding studies with BMR corn silage have re sulted in greater milk yields (Rook et al., 1977; Block et al., 1981; Stallings et al., 1982). However, others ha ve 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 (Frenchi ck 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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15 Bal et al. (2000) evaluated Pioneer 3563 as a conventional hybrid (CH) and Cargill F657 as a BMR hybrid in feeding trials with lactati ng dairy cows. They found lower NDF, ADF and lignin concentrations for BMR vs. CH. Dry matte r intake was not different between treatments groups, perhaps due to higher forage concentratio n in the BMR diet. Milk production was lower for cows fed the bm3 than the CH hybrids. M ilk 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) stat ed that though BMR hybrids ha ve 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 dige stibility was attributed to greater DMI for the bm3 mutant treatment (Rook et al., 1977), because total tract digestib ility 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 poten tial digestibility. Brown midrib 3 (bm3) is a gene mutation that has been incor porated into corn plants to imp rove fiber digestibility. This bm3 mutation resulted from structural changes in the caffeic acid O-methyltransferase (COMT) gene, which encodes the enzyme O-methyltransferase (COM T; EC 2.1.1.6) involved in lignin biosynthesis. Therefore, the lignin biosynthesis in bm3 is restricted a nd structural carbohydrates are more accessible by ruminal microorganisms. Oba and Allen (2000) showed th at, in spite of incr eased in vitro NDF digestibility (NDFd), bm3 corn silage did not have greater NDF digestib ility 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 fora ges. These authors noted that

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16 the bm3 corn silage had a greater passage rate fo r indigestible NDF and NDF, and surmised that enhanced in vitro digestibility of NDF might i ndicate 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) Ca rgill F337 (Cargill), which is a BMR hybrid, and 3) Pioneer 3861 (Pioneer), which is a dual purpo se hybrid for silage a nd grain yield. Using a plot trial, they found no differences in plant popu lation, infected ears, or lodged plants between hybrids. However, it should be not ed that there was no excessive ra in 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 dr y matter digestibility (IVTDMD) and in vitro neutral detergent fiber digestibility (IVNDFD), whic h 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 fe d 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 attribut ed 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 ru minal 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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17 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 diges tion of dietary starch strongly influences the nature of the end products of di gestion and how starch is utilized by the animal (Nocek and Tamminga, 1991; Huntington, 1997). Th erefore knowledge of the rate of ruminal starch degradation of a hybrid is important in ration formulation. Some authors reported that the lower in situ degr adability of starch in flint corn was caused by a lower proportion of the rapidly degradable frac tion, a lower rate constant of degradation, or both (Michalet-Doreau and Champion, 1995; Verbic et al., 1995; Phili ppeau and MichaletDoreau, 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 unens iled 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 main ly due to a difference in the rapidly degradable fractions (34.8 and 9.9%) of the respective hyb rids. 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 produc tion from dairy cattle can be increased by replacing dietary conventional co rn 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 ru minal microbes. Using oilseeds such as soybean

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18 ( Glycine max ) or high-oil corn (HOC) as the fat sour ce may slow the release of oil into the rumen and lessen ruminal biohydrogenation (Aldri ch et al., 1997), which may minimize ruminal disturbances while still delivering fatty acids to the animal. High-o il 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 con centration is typically 1 to 2% units higher (Dado, 1999). Dietary feeds that contain li pids 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 (5 7%) and high-oil (55%) hybrids. Lysine and other essential amino acid (AA) c oncentrations 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 cont ains 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 re sult 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 protei n 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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19 livestock indicate that feeding HOC improves feed efficiency and increases rate of gain over livestock fed conventiona l corn (Lambert, 2001). Whitlock et al. (2003) evaluated the performan ce 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 con centration 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) wh en cows were fed the HOC. Unsaturated fatty acid concentration increased (P < 0.01) and satu rated fatty acid concentration decreased (P < 0.03) when cows were fed the HOC di ets 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 s ilage was processed, the TDN concentration of HOC silage was similar to that of conventi onal silage. Kernel processing increased TDN concentration of the conven tional 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 conve ntional 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 c oncentration and that of processed corn silage was largely caused by increased starch diges tibility. 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 be tween processing treatments when high oil corn silage was fed, and no interaction was observed be tween varieties and processing for FCM yield.

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20 The variety of corn silage did not affect milk fa t 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 le ad to improved digestibility and better animal performance (Tolera and Sundstol, 1999; C ox and Cherney, 2001). Thomas et al. (2001) reported that Novartis NX3018 corn hybrid (s elected for increased leaf proportion and digestibility) had a higher proporti on of stover and lower proportion of grain compared with their Novartis NF29-F1 dual-purpose corn hybrid despite the use of sim ilar plant populations, their similar DM yields, and similar percent ba rren and lodged plants. Even though the nutrient composition of the two corn hybrids was rela tively similar, NX3018 had higher IVTDMD and IVNDFD both before and after ensiling in mini silo s 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 cont aining N29-F1 corn silage. Bal et al. (1998), however, reported that cows fed TMRs containing leafy or highgrain corn silages had similar milk yields. Bal et al. (2000) evaluated My cogen 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 popula tions. A diet containi ng the LFY hybrid diet resulted in lower DMI and higher milk fat perc entage compared with one containing the CH hybrid, though milk yield did not differ among tr eatments. Apparent digestibilities of DM, organic matter (OM), ADF and NDF were hi gher for diets containing CH than LFY.

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21 Kuehn et al. (1999) grew and fed 3 corn hybr ids: 1) Mycogen TMF94, (94-d maturity) a leafy hybrid, 2) Dekalb 442 (Dekalb Genetics Co rp., 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 concen tration 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 ba sis) silages. The leaf y silage had greater IVNDFD compared with the other hybrids. Dry ma tter 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. Di etary treatment did not affect yi elds of milk and 3.5% FCM, or milk composition. Clark et al. (2002) compared a leafy hybrid (M ycogen TMF94) selected for its silage yield and leafiness (94-d maturity) with a high grain corn hybrid (Pion eer 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 co mpared with a control grain t ype 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 yi eld, 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 digest ible (Tolera and Sundstol, 1999). Corn silage yield decreased by 15% as the cu tter bar was raised from 15.2 to 45.7 cm above the soil surface; however, silage quality (milk pe r ton) increased (Lauer 1998). Cummins and

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22 Burns (1969) reported that corn forage yields decreased by about 18% but that IVTD increased by 60 g kg1 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 kg1, NDF digestibility increased by 8 g kg1, and starch concentration increased by 27 g kg1. 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 an imal response to harvest date and cutting height of three corn hybrids, Pioneer 34B 23 (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 cont rast, 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 cu tting 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. Aver age stover IVTD increased by 16 g kg-1 as cutting height increased from 15 to 30 cm but remained unchang ed as cutting height increased to 46 cm.

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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 concentr ation. Half of the fo rage on plots containing each variety was cut at a height of 10.2 cm (normal) and the remaini ng half was cut at a height of 30.5 cm (high). They reported that corn silage ha rvested 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 concentra tion, yield of milk fat and protein, or energycorrected milk yield (ECM) were observe d among varieties or cutting heights. In a trial utilizing several leafy corn silage hyb rids 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 th e concentrations of ADF, NDF, and ADL but increasing th e 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) observe d 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 s ilage cut at height of 23 cm (NC) or 71 cm

PAGE 24

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 dige stibility 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 harves ted, ensiled, and fed to lactat ing 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 gr ain portions (kernel). As the corn plant matures, the ratio of stover to grain decreases, and dige stibility of the whole plant te nds 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 I VDMD (Russell, 1986; Tolera et al., 1999). The NDF concentration of whole plant corn silage dec lined as maturity advanced from milk to 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 ML to black layer (BL). As kernel fill increased from 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 in crease in starch concentration and a decrease in fiber concentration (H arrison et al., 1996; Bal et al., 1997). Bal et al. (1997) evaluated the effect of harvestin g corn silage at four stages of maturity on the performance of dairy cows. They found that moisture concentrati on declined from 69.9 to 58.0% as maturity of the corn advanced from th e early dent (ED) stage to the BL stage; and concentrations of NDF and ADF declined while starch concentration in creased. However, no decline in NDF and ADF concentration or increa se in starch concentration was observed from the ML stage to the BL stage.

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25 Poor starch fill (and grain yiel d) can cause photosynthetic energy to remain as sugar in the stover and leaves, thus diluting fiber content bu t not yielding the expect ed net energy (Fairey, 1983; Coors et al., 1997). Johnson and McClure ( 1968) reported an increa sing concentration of soluble carbohydrate in stalks fr om 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 fo rage and silage increased and stover quality decreased as harvest time progr essed through the growing season. Generally, forage quality was always lowest when ha rvest 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, qu ality and performance indices will remain at 95% of the optimum values if co rn 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 kg1 of DM concentration in an ir rigated 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. (1 993), 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 con centration increased by an average of 3.2 and 2.9 percentage units of NDF and ADF respectively during the pe riod from soft dough to no ML.

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26 Whole plant fiber concentration generally declin ed from soft dough to ML and then plateaued after ML. Decreases in whole plant fiber c oncentration from soft dough to ML averaged 7.6 and 4.4 percentage units for NDF and ADF, respectively. Stage of maturity has important effects on ma ny characteristics of corn crops grown for silage. Total crop yield, grain and DM concen tration, stover digest ibility (Daynard and Hunter,1975), ensiling losse s (Giardini et al., 1976), and silage intake (Malterre, 1976) can all be influenced by crop maturity and are important co nsiderations 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 b een to harvest corn plants when the ML is half to three quarters of the way down the kern el. 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 (Wie rsma 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 Harri son et al. (1996) found higher milk production for cows fed silage from w hole-plant corn harveste d at the one-half milkline 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, a nd harvesting at MLS 2-3 (under Australian conditions) would provide near maximum yiel d, optimum DM content for ensiling, and high digestibility. Whole-crop DM concentration has been a usef ul determinant of the correct stage of harvest. The ideal DM concentration for th e coincidence of optim um 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 sila ge can be achieved. Harvesting forages when

PAGE 27

27 they are too wet or too dry makes the silage suscep tible to effluent losses and respiration losses, respectively (Barnett, 1954). Ensiling crops with lower DM concentration also poses a risk of poor fermentation while adequate pa king of high DM crops in the si lo 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 carbo hydrates and IVDMD decreased and fiber concentration increased in stover with advancing maturity (Russell, 1986). Russell et al. (1992) reported that IVDMD of corn stover decr eased 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 pl ant maturity and digest ibility of whole plant corn silage. Hunt et al. (1989) studied maturity effects of si x corn hybrids across 2 yr and two locations. Concentrations of NDF and ADF in th e 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 dige stibility increased with advancing plant maturity until DM concentration reached 35 to 40%, but Daynard a nd 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.

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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 st arch digestibility (Philippeau and MichaletDoreau, 1997). Animal performance Two continuous studies (20 wk and 4.4 wk, re spectively) were conducted to determine how maturity at harvest of corn silage affects dairy cows in early lactation (H uber et al., 1965; 1968). In the first study CP and crude fi ber concentration tended to decr ease and nitrog en-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 produc tion (P < 0.08) increased as DM of the corn silage increased from 25.4 to 33.3% DM. Milk co mposition, 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). L actic and acetic acid concentrations declined and ADIN increased as matu rity of corn silage advanced from 36 to 44% DM. Milk production, DMI, and corn silage intake tended to be greatest fo r 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 tw o trials with primiparous Hols tein 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 diges tible energy estimates. In recent studies, the

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29 concentrations of NDF, ADF, and CP tended to decline and DM and starch increased with advancing maturity from milk to BL stages (H unt et al., 1989; Xu et al., 1995; Harrison et al., 1996; Bal et al., 1997). In addition, silage pH was lowest and lact ate 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 di fferences in DMI or milk fat yield were found (Harrison et al., 1996; Bal et al., 1997). In c ontrast, milk and milk protein yields were maximized when corn silage was harvested between and ML (Harrison et al., 1996; Bal et al., 1997). Harvesting corn silage at BL maturity resulted in decrea sed total tract di gestibility of starch by approximately 5 and 9 pe rcentage units, respectively, when compared with corn silage harvested at ML and 1/2 ML (Harrison et al., 1996; Bal et al., 1997). Forouzmand et al. (2005) also found that feeding corn silage harves ted at BL stage of maturity decreased TMR, silage and nutrient intake but did not have a ma jor impact on performance of mid-lactation dairy cows. Most of these studies suggest that the DM c oncentration ranges at ha rvest that optimize the nutritive value of corn silage and animal pe rformance are between 30 to 39% DM and to ML. Factors Affecting the Fermentation of Corn Silage Important criteria for the effec tive preservation of an ensile d 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 pr oduce silage that is st able under anaerobic

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30 conditions. However, several fa ctors affect lactic acid produc tion 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 (Woolfo rd, 1984). MacDonald et al. (1991) suggested that pH tends to incr ease and organic acids tend to decline as maturity advances because there is less fermentable substrate availabl e. McDonald et al. (1991) suggested that the lower pH of less mature corn silage could be related to higher mois ture and water soluble carbohydrate concentrations. Others also have reported a decline in lact ate (Huber et al., 1968; Bal et al., 1997; Johnson et al., 1997), acetate (Huber et al., 1968; Bal et al., 1997), and etha nol (Bal et al., 1997) concentration as maturity advanced. However, Johnson et al. (2002) showed that lactate and acetate concentrations and pH were similar acro ss different maturities of corn silage in two experiments. In the first experiment, Pion eer hybrid 3845 was harveste d at 1) the hard dough stage, 25.3% DM, 2) ML, 28.5% DM, and 3) ML, 27.9% DM. In a second experiment at ML, 27.1% DM, ML, 33.3% DM, and BL, 38 % DM. Etha nol concentration was greatest (P <0.0001) at the advanced maturity stage (two-third s 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 to ML and ML to BL respectively, and they found that pH was less acidic as maturity increased. Inoculants Inoculation of forage crops with homofe rmentative lactic acid bacteria (LAB) can improve silage fermentation (Muck and Bolsen, 1991) if sufficient fermentable substrate is available

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31 (Muck, 1988). Inoculation of grass or legume s ilage with bacteria ha s lowered silage pH, reduced NH3-N, and increased the lact ate: 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), a nd 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 fi rst 4 to 7 d of fermentation has been increased in some studies (Bolsen et al., 1989). Hunt et al. (1993) studied th e effect of two corn hybrid s (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 si lage 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) reporte d 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 affect ed; propionic and butyric acid were generally undetectable. The small difference in concentr ations of lactic, acet ic, and propionic acids between the silages from forages inoculated with propionibacteria and the control silage suggests that the added propionibacteria did not affect normal metabo lic activity with respect to carbohydrates and lactic acid during the ensiling period.

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32 Chop Length Particle size plays a key role in digestion and passage of f eed through the gastrointestinal tract of ruminants and th erefore in feed intake. Fernandez and Michalet-Doreau (2002) studied the fermentation characteristics of four corn silages (Safrane variet y, 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 variab les. At the late maturity stage, coarselychopped silage was more fermented than the fine s ilage, resulting in higher lactic acid (52.5 vs. 37.1 g/kg DM) and ethanol (4.7 vs. 1.5 g/kg DM) con centrations, despite the slightly higher DM concentration. Fernandez et al. (2004) compared two corn hybr ids of whole plant corn silage (WPCS) at two theoretical chop lengths (TCL), namely fine (5.0 mm) and coarse (1 3.0 mm). They found that lactic acid concentration was greater for th e 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 c oncentration and DM loss are affected by mechanical processing (Johnson et al., 1997). Roja s-Bourrillon et al. (19 87) 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 ke rnel processed corn sila ge 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 co rn silage than unprocessed silage. However, Dhiman et al. (2000) found similar pH fo r processed and unprocessed corn silage.

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33 Chemical Additives Britt and Huber (1975) reported that high con centrations of ammonia, but not urea, depressed lactic acid formati on 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 gr owth 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 addi ng 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, th e effects of the propionic acid-based additive on silage fermentation were unremarkable. Factors Affecting Aerobic St ability of Corn Silage Yeasts Yeasts are facultative, an aerobic, heterotrophic microorga nisms and are considered undesirable in silages. Silage yeas ts 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 ethano lic 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 th e 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 s ilage. Some authors reported that during the first weeks of ensiling, yeast populat ions can increase up to 107colony forming units per gram (cfu/g),

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34 though prolonged storage will lead to a gradual d ecrease in yeast numbers (Jonsson and Pahlow, 1984; Middelhoven and Van Balen, 1988). The pres ence 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 indicati ve of aerobic instability Molds and Mycotoxins Molds are eukaryotic microorganisms that de velop in silage when oxygen is present. Silage infested with mold, is usually easily id entified by the large filamentous structures and colored spores that many species produce. Mold species that have regula rly 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 nega tive effect on human and animal health. Scudamore and Livesey (1998) reported that such mycotoxicose s 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 he avily 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 pres ent (Nout et al., 1993). It is possible to have visible molds without mycotoxins. Therefore, the visible mold-mycotoxin occu rrence relationship is not clear. Mycotoxins are now more freque ntly associated with crops li ke corn silage that include grain and stover fractions Recently mycotoxins in corn silage have been implicated as the cause

PAGE 35

35 of dairy herd health problems during years with near ideal growing cond itions 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). Th erefore, the Food and Drug Administration stipulated that the concentration of aflatoxi ns in US should not exceed 20 ppb in feeds and 0.5 ppb in milk. Molds within the genus Fusarium produce se veral classes of si gnificant mycotoxins including the fumonisins, thicho thecenes and zearalenone (DMe llo et al., 1999). Fumonisins are produced by Fusarium proliferatum and F. verticillioides as well as numerous other related Fusaria. These two species are extremely comm on on corn plants and ca use ear and stalk rot diseases (Payne, 1999). In additi on, 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 s ilage during the feedout phase are important in silage preservation (Bolsen et al., 1996). Failure to achieve such conditions may cause lower

PAGE 36

36 recovery of nutrients, and th e production of poor quality sila ge 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 mustine ss occurring a few cm to several m on the face or surface of the silo during feedout. Oxygen is th e 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, ra pid filling, adequate packing, and covering with plastic. This exclusion of oxygen from the s ilage promotes rapid fermentation by anaerobic hetero and homofermentative bacteria, thereby re ducing the growth of yeasts and molds during the initial stages of fermentation. Microbial Inoculants Higginbotham et al. (1998) examined the e ffect of microbial in oculants containing propionibacteria eith er 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 l onger time to reach their peak temperature. They concluded that the microbial inoc ulants evaluated did not prevent detrimental changes in quality when corn silage was exposed to air. Howeve r, propionic acid-based preservatives have been used to improve the aerobic stabil ity of corn silages because of th e 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 relativ ely low concentrations (0.1 to 0.2% of fresh forage weight) of several additives that contained buffered propionic acid as their primary active ingredient.

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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 stab ility of silages by i nhibiting 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 en siling at the rate of 106 cfu per gram of fresh material, L. buchneri has increased aerobic stability of hi gh moisture corn, corn silage, alfalfa silage, and small-grain silages relative to untreated controls (Muc k, 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 yeas ts (Driehius, et al., 1999). Yeast and mold counts of L. buchneri inoculated silages are generally lower at feedout and do not increase as ra pidly 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 instab ility are expected. Corn silage, small-grain silages, and high-moisture corn are more susceptib le to spoilage once exposed to air than legume silages and therefore the latter often re spond 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 stabi lity 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 heterola ctic fermentation that resulted in a marked enhancement in aerobic stability. Ni shino et al. (2004) repor ted that population of yeas ts was lowered to about

PAGE 38

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 th e concentrations of lactic and acetic acids (Muck and Kung, 1997), decreased proteoly sis (Huber et al., 1979; Huber et al., 1980), improved DM r ecovery (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 s ilage improves aerobic stability because of its fungicidal properties (Depasquale and Montville, 1990). Kung et al (2000) studied the effect of ammonia hydroxide (application ra te of 0.30% N of fresh fora ge (35 g DM/100g) weight) on corn silage. They found that th e 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 sila ges. The number of yeasts in control silages increa sed 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 afte r treatment with ammonia. Britt and Huber (1975) also reported that ammoni ation decreased numbers of funga l colonies in corn silage within 30 min of initial treatment. Ammoniation at moderate concentration (l ower than 0.7%) decreased yeast and mold counts in corn silage; however, an undesirabl e 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,

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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 (O ndarza, 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. U pon 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 diet s, ages of cows, levels of milk production, a full spectrum of blood chemistry and biochemical assa ys 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. Ea rly postmortem examinati on of cattle with HBS shows intestinal lesions with hemo rrhages 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 relationshi p between rumen acidosis, which facilitates the passage of more starch to the cows 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

PAGE 40

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 st udies have demonstrated potential for Aspergillus species to infect the ruminant gut at va rious sites and to cause enteri c hemorrhage. Sheridan (1981) reported aspergillosis in the calf abomasum. In 1989, Jensen et al (1989) reported that A. fumigatus infected the terminal gastri c compartments, particularly the omasum. Dairy producers in Florida have had increasing inci dences of HBS in their herds a nd 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 o ccurs sporadically in ot her regions of the US (Kelbert, 2004). Variable Manure Syndrome or a drastic swing from normal to loose manure indicates rumen pH instability a nd 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 a nd 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 s poradically in a herd on the same day, without ration changes. The condition is often prevalent after corn is harvested under wet conditions.

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41 Three out of the last four co rn harvest seasons (2000, 2001, 2002 a nd 2003) in Florida have been wet (Kelbert, 2004). During the we t years, silage was typically harvested at below 32% DM and during the dry years silage was usually harves ted above 32% DM. During these wet harvest years, if the harvest management or rain c onditions resulted in a DM below 32% increased incidence of VMS occurred (Kelbert, 2004). VM S was not seen prior to 1998 when it was common to harvest corn earlier (<30% DM) rather th an 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 Florid a 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 pl ant 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 a lteration of genes involved in the on set of senescence and the regulation of its rate of progress. However, SG in the re maining two classes is cosm etic, because the plants are green but lack photosyntheti c competence. This may be due to a loss in photosynthetic capability that normally accompanies senescen ce 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 rapidl y 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 understandi ng of the physiological processes underlying the development of this tr ait in such hybrids. Selection for improved resistance to disease and reduced leaf senescen ce at high plant densitie s (Cavalieri and Smith,

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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 remobiliza tion to actively growing kernels of maize (Borras et al., 2003). During senescence, leaves lose their greenne ss as a result of a decline in chlorophyll concentration, providing a clear visual symptom of leaf senes cence. Delayed appearance of visual symptoms of leaf senes cence 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 f illing (Borrell et al., 2001). Borrell et al. (2001) suggested that roots of th e 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 grai n 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 in dications of greater N allocati on to the kernels of the SG corn. Green leaf area at physiological maturity has prov ed to be an excellent indicator of SG, and has been used successfully to select drought-res istant sorghums in the US (Rosenow et al., 1983). The duration of leaf senescence is a functi on 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 an d Andrade, 1995) and or changes in the sourceto-sink ratio, that is, the ratio between assimilate supply and the potential of the grain to

PAGE 43

43 accommodate assimilates (Tollenaar, 1977). Premat ure 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 l eaf 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, Sude bi and Ma (2005) report ed that three corn hybrids contrasting in leaf number and stay-g reenness grown with a precisely controlled N supply did not differ in N acquisition, partitioning, a nd remobilization to different plant parts at physiological maturity. The SG hybrid remained gr een at physiological maturity only when there was an unrestricted N supply, indicating that SG is a trait that is exhib ited only under adequate N availability. During post-anthesis drought, genotypes po ssessing 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 effici ency, were largest from 3 wk postsilking 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 la te grain filling. Corn silage hybrids with the SG characteristic, grown at re latively high plant populations, may show improved disease resistance compared with conventional hybrids. This benefit may,

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44 however be outweighed by lower whol e plant DM in SG cultivars th an other cultivars as a result of their higher proportio n of green leaf (Hav ilah 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 th is may have limited whole-plant yi eld by providing less sink for photosynthate as the crop progresse d through the later stages of growth. It is notable that yield of DM was only higher in C cultivars than SG cul tivars in the warmest of the four environments, indicating that environmenta l effects on yield are likel y 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 ha d 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 co rn 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 sc ore equivalent to 2.5. The SG characteristic further invalidates the use of the milk line for pr edicting harvest dates for corn forage destined for ensiling. In situations of relatively low late-season te mperatures, without the occurrence of frosts to kill the leaves, the starch in th e endosperm of SG hybrids may become progressively harder with advancing grain maturity while the stover (l eaf and stem) remains too wet for ensiling (Wilkinson et al., 1998). This can lead to lowe r grain digestibility and production of significant amounts of effluent during the ensiling period. Any advantage in crop yield due to the SG

PAGE 45

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 hy brids did not compare such hybrids to conventional hybrids. The objectives of this st udy were the following: To determine the optimum maturity st age for harvesting SG corn varieties destined for silage produc tion, and to determine if th ere are differences in the fermentation and aerobic stability of hybrids with contra sting 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.

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46 CHAPTER 3 EFFECT OF MATURITY AT HARVEST OF CORN HYBRIDS DIFFERING IN STAYGREEN RANKING ON THE QUALITY OF CORN SILAGE Introduction Corn silage has been used across the US as a source of energy and dige stible fiber for dairy cattle. Florida dairy producers have been concerned about a po ssible link between reduced milk yield, digestive upsets and Hemorrhagic Bowel S yndrome 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 tr ait (i.e., the phenotypes that exhibit delayed senescence) as having greater wate r and chlorophyll conc entration in the leaves at maturity. Therefore, high SG rankings are genetically co rrelated with high stal k and leaf moisture concentrations (Bekavac et al., 1998). Four cl asses of SG have been identified by Thomas and Smart (1993). The first two classes are functiona lly SG and may occur after alteration of genes involved in the onset of senescence and the regula tion 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 phot osynthetic capability that normally accompanies senescence combined with mainte nance of leaf chlorophyll, or it may be related to premature death seen in herbarium specimens or frozen foods that retain greenness be cause 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 h ealth and greater lodging resistance late in the growing season, typically beyond the black la yer stage. The dry-down rates of the ear and stover of such SG hybrids is async hronous. The ears mature faster than the stalks

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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 and kernel milk line. Such results led to the widely held notion that corn intende d for ensiling should be harvested at the 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 im plies that the traditional relation ship 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 harv esting corn varieties destined for silage production, and to determine if there are differences in the nutr itive value, fermentation and aerobic stability of hybrids with contra sting SG rankings. Materials and Methods Plot Trial Planting and establishment Two varieties of corn with high (HSG) SG rankings (Pioneer 31Y43 (Pioneer Hi-Bred Internat ional, Des Moines, Iowa) and Croplan Genetics 827 (Croplan Genetics, St. Paul, MN) were compared with two varieties with aver age (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.

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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 in to 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 th e whole plant sample reserved for chemical analysis were chopped (2 cm) and representatively subsampled (0.2 kg) for DM analysis (105C for 24 h). Representative samples (6.5 kg) of th e herbage reserved for ensiling were placed in polythene bags within quadruplicate 20-L mini-silo s (one silo per plot) a nd sealed. Weights of the empty and full silos were recorded, and silos were then stored for 107 d at ambient temperature (25C) in a covered barn. Chemical analysis Dried whole plant, stover and ear sa mples were ground to pass through a 1mm screen in a Wiley Mill (A. H. Thomas, Philadelphia, PA) and analyzed. Ash concentration was determined in a muffle furnace at 550C for 6 h. Starch was determined using the procedure of Holm et al. (1986). The anthrone reaction a ssay (Ministry of Agriculture Fisheries and Food, 1986) was used to quantify water-soluble carbohydr ates (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 Incubato rs (ANKOM Technology, Macedon, NY). The

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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 weig hts were recorded at s ilo opening and silages from each treatment were subsampled for DM de termination (450 g), sila ge juice extraction (20 g), microbial analysis (400 g), chemical analysis (800 g) and aerobic stabi lity (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 Bact eriological 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 opentop polystyrene box. The silages were covered with two layers of cheesecloth to prevent dryi ng. 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 stab ility was denoted by the hours taken for a 2C rise in silage temperature above ambient temp erature (23C). Silage DM concentration was determined at 60C in a forced air oven for 48 h. Ash concentration was determined in a muffle furnace at 550C for 6 h. Silage juice was obtai ned 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 me ter (Accumet, model HP71, Fisher Scientific, Pittsburgh, PA). The f iltrate was centrifuged at 4C and 21,500 x g for 20 min and the supernatant was frozen (-20C) 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 Perfor mance 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

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50 for the Technicon auto analyzer (Technicon, Ta rrytown, 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 sa me 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 maturi ty at harvest. The data were analyzed using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC) and the following model: Yijkl = + Ci + SGj + Mk + Bl + Eijkl where = 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. Po lynomial 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 proced ure of SAS. All intera ctions were examined: stay-green x maturity, stay-gre en 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 co nditions and may not refl ect quality differences

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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 conven tional and SG corn hybrids harvested at 25.8 to 43.5 g DM/100 g and attributed this to earlier flowering in the conve ntional hybrids, which increased the time available for ear development and grain filling between flow ering and harvest. Whole plant DM, ash, starch and CP concentr ations were unaffected by SG ranking. Unlike Croplan Genetics hybrids, Pioneer HSG hybrids had greater DM and starch concentrations and IVDMD, and lower concentr ations 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 ma turity. 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 tota l N uptake than conven tional hybrids (Ma and Dwyer, 1998; Rajcan and Tollenaar, 1999; Borrell and Hammer, 2000; Borrell et al., 2001). Neutral and acid detergent fibe r 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.

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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 depende d on hybrid source (Matur ity x source interaction, P < 0.01) Whole plant DM and starch c oncentrations incr eased linearly ( P < 0.001) with maturity, whereas CP, NDF and ADF c oncentrations 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 vegeta tive to reproductive growth in the plants. Ash concentration changed quadratically with maturity at rates th at differed with hybrid s ource (Maturity x source interaction, P = 0.05). Changes in WSC concentration wi th 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 Matu rity 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 concentrati ons (Table 3-2) than HSG hybrids (258 vs. 239 g/kg) though the differen ce 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 mois ture in leaves than conventional hybrids. The results also agree w ith 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, th e 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

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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 root s and leaves than SG. The greater total N accumulation by the SG hybrid s was possibly due to the fact that they remained green after physiological maturity such that they took up N fo r a longer period of time than early-senescing hybrids (Sudebi and Ma, 20 05; 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 (B orrell et al., 2001). Unlike that of Pioneer hybrids, the stover of Croplan Genetics HSG hybrids tended ( P = 0.08) to have greater NDF concentrati on (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 hyb rids, indicating a tendency for greater hemicellulose concentra tions in the stover of HSG hy brids (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 obtaine d from the corresponding whole plants. Stover DM increased linearly ( P < 0.05), and ash concentratio n tended to increase linearly ( P = 0.06) with maturity. Concentrations of CP and IVDMD decreased linearly ( P < 0.001) with maturity, whereas concentrati ons 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).

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54 Unlike Croplan Genetics hybrids, Pioneer HSG hybrids had greater DM and CP concentrations in the ear than thei r ASG hybrids (SG x source interaction, P < 0.05; Table 3-3). High SG hybrids also had greater ( P < 0.01) ear ash concentrati on than ASG hybrids (20 vs. 18 g/kg DM) but ear WSC concentrations were si milar among hybrids. The results from the Pioneer hybrids support those of Ettle and Sc hwarz (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 resu lts contrast with othe rs 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), Cr oplan 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 (Wilk inson and Phipps, 1979), HSG hybrids should have greater starch concentra tion than ASG hybrids. The cont rasting trend for the Croplan Genetics hybrids is partly attributable to fi ber concentration differe nces between hybrids. Neutral and acid detergent fi ber concentrations tended ( P = 0.01) to be greater in Croplan Genetics HSG vs. ASG hybrids, but an opposite trend was eviden t among Pioneer hybrids (SG x source interaction, P < 0.001). Consequently, as in the unensiled whole pl ant and unensiled stover, the IVDMD of ensiled HSG hybrids from Cr oplan 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 attributab le to their greater NDF and ADF concentrations. The faster

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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 cont radicts finding of similar digestibility between HSG and conventional hybrids by Australian res earchers (Havilah and Kaiser, 1994), possibly due to differences in the prevai ling temperature and humidity duri ng the growth of the hybrids. Kernel processing may be beneficial for im proving energy availability from the Croplan Genetics HSG hybrids. Water-soluble carbohydrate c oncentration was greater ( P < 0.05) in HSG (7.1 vs. 6.4 g/kg of DM) than ASG hybrids, and CP c oncentration 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 va riety had greater CP concentrati on 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). Th is is probably related to greater retention of chloroplast proteins and greater capacity fo r N uptake in SG hybrids (Borrell et al., 2001). Dry matter and starch concentr ations 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 IVDM D and in situ degradability of corn silage remained unchanged within the ra nge of maturities examin ed 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 mo re acidic pH their ASG hybrids (3.73 vs. 3.77; SG x source interaction, P = 0.015). Nevertheless, the differen ces were practically insignificant.

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56 The concentrations of NH3-N and most organic acids were similar in HSG and ASG hybrids and butyric acid was not dete cted in the silages. Ettle a nd 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 concentra tion 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 ag rees 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 sufficien t to cause rapid deterioration of the silage. Yeast and mold counts changed wi th 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, Pione er HSG hybrids had greate r ear and whole-plant DM concentrations than their ASG hybrids; t hough 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 lowe r IVDMD in the unensiled whole-plant, the stover, and the silage than the ASG hybrids, indi cating that nutritive valu e 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 sour ces. This work therefore suggests that in some corn hybrids, high SG rankings may be asso ciated with a different moisture distribution

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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 di gestible DM, starch, DM concentration, and yeast counts increased, fiber components, CP and WSC decreased, whereas IVDMD was unchanged. However, these maturity-related cha nges differed with hybrid source and SG ranking. It is concluded that the best combination of DM yield, nutritiv e value, fermentation quality and yeast counts were obtained when the corn hybrids were harvested at 32 g DM/100g.

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58Table 3-1. Yield and chemical composition of unensiled whole plants from corn hybrid s differing in stay-green (SG) ranking, maturity and source. P value Maturity High SG Average SG SE SG Maturity Source2 SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 0.0010.001 ns g/kg DM 2 275 276 244 355 3 347 237 279 297 WSC 1 91 101 91 127 8.9 0.003ns 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN WSC = Water-s oluble carbohydrate

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59Table 3-1. Continued P value Maturity High SG Average SG SE SG MaturitySource SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 <.001ns 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN WSC = Water-s oluble carbohydrate

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60Table 3-2. Chemical composition of unensiled stovers from corn hybrids differing in st ay-green (SG) ranking maturity and sour ce. P value Maturity High SG Average SG SE SG Maturity Source SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 WSC 1 124 106 101 158 23.2 ns ns 0.008 ns 0.011 0.006ns 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN WSC = Water-s oluble carbohydrate

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61Table 3-2. Continued P value Maturity High SG Average SG SE SG Maturity Source SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN

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62Table 3-3. Chemical composition of unensiled ears from corn hybrids differing in st ay-green (SG) ranking, maturity and source. P value Maturity High SG Average SG SE SG Maturity Source2SG*mSG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( m ) ( c ) DM, 1 318 230 297 306 22.5 0.109 <.001, L ns ns 0.012 0.006ns 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 WSC, 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN WSC = Water-s oluble carbohydrate

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63 Table 3-4. Chemical composition of corn silages made from hybrids differing in stay -green (SG) ranking, maturity and source. P value Maturity High SG Average SG SE SG MaturitySource SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 <.001ns ns g/kg DM 2 283 244 264 355 3 320 308 297 373 WSC 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN WSC = Water-s oluble carbohydrate

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64Table 3-4. Continued P value Maturity High SG Average SG SE SG Maturity Source SG*mSG*c m*cSG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 <.001ns 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 <.001ns 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN

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65Table 3-5. Fermentation indices of corn si lages silages made from hybrids differing in stay-green (SG) ranking, maturity and s ource. P value Maturity High SG Average SG SE SG MaturitySource SG*m SG*c m*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( m ) ( c ) 1 3.8 3.7 3.7 3.7 0.03 0.09 0.003, L ns ns 0.015ns ns pH 2 3.8 3.8 3.7 3.8 3 3.8 3.7 3.8 3.8 NH -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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN

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66Table 3-5. Continued P value Maturity High SG Average SG SE SG MaturitySource SG*m SG*cm*c SG*m*c PN31Y43 CPL827 PN32D99CPL799 ( 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 Maturity 1, 2 and 3 = 25, 32 and 37 g DM/100g at harvest, respectively. Source = Pioneer (PN) Hi-Bred Inte rnational, Des Moines, Iowa and Cropl an (CPL)Genetics, St. Paul, MN

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67 CHAPTER 4 EFFECT OF STAY-GREEN RANKING, MATU RITY AND MOISTURE CONCENTRATION OF CORN SILAGE ON THE HEALTH AN D PRODUCTIVITY OF LACTATING DAIRY COWS Introduction Silage producers in Georgia and Florida have be en concerned that ensi ling 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 ( to 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 va riants with delayed leaf senescence due to partial or complete inhibition of deconstruction of the photosyn thetic apparatus during leaf senescence. Although the SG phenotype is supe rficially similar in all crop species and genotypes, the genetic and physiolo gical basis is diverse. Sor ghum genotypes with the SG trait continue to fill their grain normally under dr ought (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 di sease 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 hi gher 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 facilita ting combining. However, this trait pr esents problems for silage producers because it causes asynchronous maturity and dry down rates in the ear and the stover. The

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68 presence of the characteristic implies that the tr aditional relationship between whole plant silage moisture concentration and kernel milk line ma y 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, resp ectively (Barnett, 1954). Crops en siled with excess moisture are often poorly fermented due to pro liferation of butyric acid-produci ng clostridia. Delaying harvests of SG hybrids to allow the stover to dry can predispose to disease infe station. It is also difficult to ensile crops with excessive DM concentrations becau se 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 charac teristic affects the perf ormance 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 hy brid SG ranking, maturity and water addition at ensiling on health, feed intake a nd 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 dietar y treatments for two, 28-d periods. Each period consisted of 14 d for adaptation to a new di et and 14 d for sample collection. Near isogenic corn hybrids with high SG (Croplan Genetics 69 1) 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

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69 varieties were planted on 6 April, 2005, harv ested on 12 July, 2005 at 26 g DM/100g (Maturity 1) and packed into 32-ton, 2.4-m wide Ag-Bags w ith 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 pi pe to simulate rainfall. The quantity of water added was the maximum amount possible that allowed normal opera tion of the bagger. Both hybrids also were harvested on 19 July, 2005 at 35 g DM/100g (Maturit y 2) and packed into Ag-Bags. The forages were ensiled for 84 d (Maturity 1) and 77 d (M aturity 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 treatme nts evaluated were the following: 1) Low stay-green hybrid (LSG) harv ested at 26 g DM/100g, 2) High stay-green hybrid (HSG) harvested at 26 g DM/100g, 3) High stay-g reen hybrid harvested at 35 g DM/100g, 4) Low stay-green hybrid harv ested at 35 g DM/100g, 5) High stay-gr een hybrid (HSG wet) harvested at 26 g DM/100g and irrigated. Cows were fed in dividually 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 befo re the beginning of the tr ial. 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 par ity, 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 trea tment 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 a nd 1800 h and milk producti on (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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70 during each week in the last 14 d of each period, preserved with potassium dichromate and stored at 4C. Milk samples were analyzed by Southeas t Milk lab (Belleview, FL ) for concentration of fat, true protein and SCC using a Bentley 2000 Near Infrared Refl ectance Spectrophotometer (Bentley Instruments Inc., Chaska, MN ). Feed efficiency was calcula ted as kg of milk/kg of DMI. Body weight was measured for 3 consecutive da ys after the 1000 h milki ng at the beginning and end of each period. Rectal temperature and the nu mber 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 (B D Vacutainer. Franklin Lakes, NJ) containing sodium heparin by caudal arteriovenipuncture on th e last day of each period. Samples were centrifuged at 2500 x g for 20 min and the plasma was frozen at -20C. Concentration of plasma glucose (Glc) was determined using a Technicon Autoanalyzer II (Bran-Luebbe, Elinsford, NY) and a method modified from Gochman and Schmid z (1972). Blood urea nitrogen was determined using an autoanalyzer method (Technicon Industria l 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 concen tration 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 digestib ility. Chromic oxide powder (Fisher Scientific, Fairlawn, NJ) was weighed into gelatin capsules (Jor gensen 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 60C 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

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71 samples per cow per period. Chromium concentra tion 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 tech nique (Schneider and Flatt, 1975). Two representative samples of the concentrate, each forage and the TMR were collected during each week of each colle ction period and composited, subsampled and analyzed for CP, NDF, ADF, water-soluble carbohydrates (WSC) and starch. Concentr ation 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 a ssay (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 ba g containing 1 kg of silage, within an open-top polystyrene box. The silages were covered with 2 layers of chees ecloth to prevent drying. The thermocouple wires were connected to data logg ers (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 2C rise in silage temper ature above ambient temperature (23C). In Experiment 2, 5 ruminally-fistulated lactating co ws were used to evaluate the effect of the dietary treatments on ruminal pH, VFA concentr ation and ammonia-N concentration, during 3 consecutive 15-d periods. Each period consisted of 14 d of adap tation 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 feedi ng on the last day of each period. The pH was measured within 20 min collection using a pH me ter (Accumet, model HP-71, Fisher Scientific, Pittsburg, PA). The ruminal fluid was acidified with 3 ml/sample of H2SO4 (50% v/v). Samples

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72 were centrifuged at 12,000 x g for 20 min, after whic h the supernatant was collected and frozen (20C) in 20-ml vials. Volatile fatty acids were measured using the method of Muck and Dickerson (1988) and a High Performance Liquid Chroma tograph (Hitachi, FL 7485, Tokyo, Japan) coupled to a UV Detector (Spect roflow 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 45C. Ammonia N was determined with a Technicon Au to analyzer (Technicon, Tarrytown, NY, USA) and an adaptation of the Noel a nd 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 = + Ti + Pj + Ck + Rl + Eijkl where : 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 = + Ti + Pj + Hk + Cl + Eijkl where : general mean

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73 Ti: treatment effect (fixed effect) Pj: period effect (fixed) Hk: time effect (repea ted 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 incubati on 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 tim e. 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 silage s 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 stab ility 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 decr eased CP, NDF and ADF concentrations. These results suggest that higher SG ranking was asso ciated with more yeas t and mold growth and spoilage when corn was harvested at 26 g DM/100g, or when water addition increased the moisture concentration of co rn harvested at 26 g DM/100g.

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74 Voluntary Intake Dry matter intake was similar across diets (T able 4-3) but intake of starch tended ( P = 0.09) to be lower for cows fed the HSG diet. Adding mo isture 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 (S G 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 kern el dry down (DD) compared to a SG variety (3.0 kg per cow), possibly due to a lower concen tration of fiber in the DD variety. Intakes of DM (DMI) and starch were not a ffected 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 harv ested 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 ( milk line; ML) or 30.5% DM ( ML). However, Ettle and Schwarz (2003) repor ted 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 ha rvested at 38 to 42% DM (17.8 and 11.8 kg of DM per cow, respectively). Bal et al. (1997) found no di fferences in DMI in corn silages with DM at harvest ranging from 30.1 to 42%. These discre pancies in maturity effects on DMI probably reflect varietal differences in th e experimental silages particularly differences in the concentration and digestibility of NDF. Cows fed LSG hybrids had greater ( P < 0.01) DM, NDF and CP dige stibilities than those fed HSG hybrids, and the difference in NDF digest ibility was more pronounced at Maturity 1

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75 (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 digestibilit ies of the HSG hybrids were largely due to lower digestibility of NDF and CP in HSG hybrids. Apparent DM and CP digestibilities were not a ffected 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 th at stage of maturity (30 to 32% DM and 38 to 42% DM) did not affect OM digestibility. Star ch 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 effi ciency of postruminal st arch digestion or more whole kernel passage from the rumen of cows fed the more mature silage (Harrison et al., 1996). Adding moisture to the Matur ity 1 HSG hybrid increased ( P < 0.05) CP digestibility (62.3 vs. 65.2%), possibly due to provisi on 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 producti on in cows fed Maturity 1 vs. Maturity 2 diets (Table 4-4). Et tle 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 exam ined 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.

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76 Cows fed HSG hybrids had lower milk fat con centration (3.5%) than those fed LSG hybrids (3.8%) when the hybrids were harvested at Matu rity 1, but the revers e 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. John son et al. (2002) reported that milk fat yield was lower ( P < 0.02) in corn harvested at 38.2% DM co mpared 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 si milar 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 concentra tion and milk fat production were not affected by maturity. The maturity-related decreas es in milk fat concentration and yield in this study are not attributable to differences in fiber concentration of the hybrid s at the two maturities, since ADF and NDF concentrations decreased with maturity. Milk protein and milk protein yi eld were not affected by maturit y. Johnson et al. (1999) also found that milk protein concentration was not af fected by maturity. However, Bal et al. (1997) reported that milk protei n 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 ( ML) or 42% DM (BL stage). They suggested that this was due to the higher star ch concentration and diges tibility 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. (2 005) 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.

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77 Body Weight and Plasma Metabolites Mean BW was unaffected by SG ranking or matur ity, 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 diet s partitioned more nutrients to BW gain. Ettle and Schwarz (2003) also reported that BW was not affected by variety or matur ity. 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 concentra tion 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 gr eater in cows fed HSG ( P < 0.05) vs. LSG (38.1 vs. 38.0 C), but the values were within the norma l physiological range. Ruminal c ontraction rate and manure score were not affected by SG ranking bu t 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 (Fi gure 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 rumi nal 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 unchange d with maturity in cows fed LSG hybrids (19.0 vs. 19.1 mg/d l) (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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78 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 43) 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 ma turity. Ruminal concentration of propionic acid (Figure 4-4) decreased with maturity in co ws 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 refl ecting the greater starch intake in cows fed the HSG wet diet. Ruminal concentration of iso-but yric acid increased with matur ity 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 matu rity interaction, P < 0.05). Ruminal concentrati on of butyric acid (Figure 45) 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 concentrat ion of iso-valeric and 2-methyl butyric acids were not affected by SG ranking but the iso-valeric and 2-methyl butyric acids c oncentrations increased with maturity in cows fed LSG hybrids (3.8 vs. 5.1 mo lar %) 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. Con centration 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 co ws fed LSG hybrids (3.1

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79 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 c oncentration decreased with maturity in cows fed LSG hybrids (99.5 vs. 75.2 mM) but cows fed HSG hybr ids 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 indicat es that the extent of fermentation was increased by this treatment (Figure 4-7). This ma y have resulted from the greater CP and starch intake and CP digestibility that occurred when moisture was a dded to the Maturity 1 HSG diet. Apparent digestibility is ofte n proportional to ruminal total VF A concentration. The disparity between these measures in this study may reflect greater post ruminal dige stion of the HSG(wet) diet. Conclusions This study shows that the effect of maturity on several perfor mance attributes of the cows was influenced by the SG ranking of the hybrids. Nevertheless, harvestin g 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 ranki ng resulted in lower apparent DM and CP digestibilities, greater BW gai n, greater though physiologically norma l rectal temperature; but did not adversely affect other health measures or milk production by the cows. No incidence of

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80 digestive upset, diarrh ea or Hemorrhagic Bowel Syndrome o ccurred in the cows. Therefore no direct link between high SG rankings in corn s ilages 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 co rn under dry conditions.

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81Table 4-1. Ingredient and chem ical 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 mix 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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82Table 4-2. Chemical composition of corn silages differing in maturity, SG ranking a nd 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 harves t, 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 > 2C.

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83Table 4-3. Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on fe ed intake and digestibility of lactating dairy cows. Maturity 1 Maturity 2 SE Effects ( P value) LSG1 HSG2 HSG(wet)3 LSG1 HSG2 SG MATSG*MATMOIST Intake, 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 0.0800.07 0.14 NDF 9.6 8.0 8.4 8.0 7.9 0.4 0.04 0.0110.05 ns ADF 6.3 5.3 5.6 5.3 5.1 0.3 0.02 0.0040.05 ns Digestibility, g/100g DM 68.4 61.6 63.9 68.4 64.7 1.2 0.001ns ns ns NDF 60.1 49.2 47.0 54.6 50.7 1.8 0.0010.12 0.03 ns CP 69.1 62.3 65.2 68.7 64.3 1.1 <.001ns 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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84Table 4-4. Effect of maturity at harvest and moisture addition to corn silages with contrasting stay-green (SG) rankings on mi lk production and composition from lactating dairy cows. Maturity 1 Maturity 2 SE Effects ( P value) LSG1HSG2 HSG(wet)3 LSG1 HSG2 SG MATSG*MATMOIST Milk, 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, 10 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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85Table 4-5. Effect of maturity and moistu re addition to corn silages with contras ting stay-green (SG) rankings on body weight a nd plasma metabolites in lactating dairy cows. Maturity 1 Maturity 2 SE Effects ( P value) LSG1HSG2HSG(wet)3 LSG1 HSG2 SG MATSG*MATMOIST BW, 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 0.030.03 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 -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 harves t, 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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86Table 4-6. Effect of maturity at harvest and moisture addition to corn silages with contrasti ng stay-green (SG) rankings on rum en 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*MATMOIST Rectal temperature, C 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 NH -N, mg/dl 19.0 27.9 21.6 19.1 20.9 2.0 0.0080.08 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 0.003ns 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 0.0010.03 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

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87 5 5.5 6 6.5 7 024681012Time after feeding, hpH LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-1. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on rumina l 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 harves t, Mat 2 = 35 g DM/100g at harvest.

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88 0 6 12 18 24 30 36 42 48 024681012 Time after feeding, hNH3-N, mg/d l 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 mo isture addition to corn silages with contrasting stay-green rankings on ruminal NH3-N concentration. LSG = Low stay-green hybrid, HSG = High stay-green hybri d, 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.

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89 48 50 52 54 56 58 60 62 024681012 Time after feeding, hAcetic acid, molar % LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-3. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on ruminal acetic acid mo lar percentage. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HSG (w et) = 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.

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90 14 16 18 20 22 24 024681012 Time after feeding, hPropionic acid, molar % LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-4. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on rumina l propionic acid molar percentage. LSG = Low staygreen hybrid, HSG = High stay-green hybri d, 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.

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91 9 10 11 12 13 14 024681012 Time after feeding, hButyric acid, molar % LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-5. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on rumina l butyric acid molar percentage. LSG = Low staygreen hybrid, HSG = High stay-green hybri d, 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.

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92 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 024681012 Time after feeding, hC2: C3 ratio LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-6. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on rumina l acetic: propionic acid rati o. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HS G (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.

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93 40 60 80 100 120 140 160 180 024681012 Time after feeding, hTotal VFA, m M LSG Mat 1 HSG Mat 1 HSG Mat 2 LSG Mat 2 HSG(wet) Mat 1 Figure 4-7. Effect of maturity at harvest and mo isture addition to corn silages with contrasting stay-green rankings on rumi nal total VFA concentration. LSG = Low stay-green hybrid, HSG = High stay-green hybrid, HS G (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.

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94 CHAPTER 5 GENERAL SUMMARY A series of studies were conduc ted 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 characteris tic is desirable for corn grai n production because it confers resistance to lodging and disease infestation to corn plants. Howe ver, this characteristic is undesirable for silage producers because it result s 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 incide nce of HBS in their cows in recent years with intake of SG co rn hybrids. Therefore there is a need for research into optimal maturity at harvest of such hybrids and the exis tence of a link between HBS and SG corn intake. The objective of Experiment 1 was to determin e 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, Cr oplan Genetics 827) were compared with two varieties with average (ASG) st ay-green rankings (Pioneer 32D 99, Croplan Genetics 799). These varieties were grown on 1 x 6 m plots and harves ted at 25 (Maturity 1), 32 (Maturity 2) and 37 (Maturity 3) g DM/100g. The harv ested forage was divided into three portions, one each for botanical fractionation (ear vs. stov er), whole plant chemical analys is 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 (25C) in a covered barn.

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95 The stover of ASG hybrids had greater DM concen trations and lower CP concentrations than those of HSG hybrids from both sources, though th ese differences tended to be more pronounced in Croplan Genetics hybrids. These results refl ect the greater green leaf and stem proportion in HSG hybrids. Unlike those of Pioneer hybrids, th e stover, whole plant and silage from Croplan Genetics HSG hybrids had greater NDF and ADF con centrations 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 h ybrids. 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 a dversely affect silage quality in this study. As the hybrids matured, DM yield, yield of di gestible DM, starch, DM concentration, and yeast counts increased, whereas fiber component s, CP and WSC decreased, consequently IVDMD was unchanged. However, the nature of these matu rity-related changes differed with hybrid source and SG ranking. It is concluded that the be st combination of DM yield, nutritive value, fermentation quality and yeast counts was obtaine d when the corn hybrids were harvested at 32 g DM/100g. The objective of Experiment 2 was to determ ine the effects of SG ranking, maturity and simulated rainfall on the qua lity 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) an d packed into 2.4-m wide, 32-ton Ag-Bags. A further treatment involved adding 15 l of water per t on of silage to forage harvested at Maturity 1

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96 to simulate rainfall at harvest. The water wa s added with a hosepipe during packing. Thirty lactating Holstein cows in mid-la ctation (92 days in milk (DIM)) were allocated randomly to the five silages for two, 28-d periods. The silages fo rmed part of a TMR consisting of corn silage, alfalfa hay and concentrate mixed at 35, 10 a nd 55 g/100g (DM basis) re spectively. Dry matter intake, digestibility, milk production and com position, blood and ruminal function parameters were measured. Intake of starch, CP, NDF and ADF were lo wer 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 digestibilit ies of DM, NDF and CP were also lo wer in cows fed HSG vs. LSG hybrids, though the difference in NDF digestibility was mo re 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 fe d Maturity 1 vs. Maturity 2 diets. Cows fed HSG hybrids had lower milk fat concentration than those fed LSG hybrids ha rvested 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 protei n concentration and yield were not affected by maturity. However, manure score, rumen contra ctions BW gain, ruminal pH, plasma glucose concentration and the efficiency of feed conversion into milk imp roved 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.

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97 Adding water to the Maturity 1, HSG hybrid re duced ruminal ammonia-N concentration but increased starch intake, CP digestibility and rumi nal VFA concentration, and tended to increase CP intake. This suggests that wate r addition improved dietary protei n and energy utilization, probably because the added water provided more conducive conditions for enzymatic nutrient hydrolysis. However water addition was associated with gr eater yeast and mold counts and poorer silage aerobic stability, reflecting the importance of harvesting and en siling corn silage under dry conditions. These experiments did not demonstrate a di rect 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 a ssociated with poorer nutritive values in hybrids from Croplan Genetics. More work is needed to investigate the cause s of HBS in dairy cows and the role of SG hybrids in the etiology of the di sease. Such studies should: (i) Compare SG hybrids to traditional non-SG hybrids. (ii) Examine diurnal fluctuations in b ody 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.

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98 LIST OF REFERENCES Adesogan, A.T., M. Huisden, K. Arriola, S. Ki m, and J. Foster. 2005. Factors affecting the quality of corn silage grown in hot, humid areas 2: Effect of a pplying two dual-purpose inoculants or molasses. J. Anim Sci. 83(Suppl. 1):383. (Abstr.) Aldrich, C.G., N.R. Merchen, J.K. Drackley, S.S. Gonzalez, G.C. Fahey, Jr., and L.L. Berger. 1997. The effect of chemical treatment of whole canola seed on lipid and protein digestion by steers. J. Anim. Sci. 75:502-511. Alii, I.R. Fairbairn, B.E. Baker, L.E. Philip, and H. Garino. 1983. Effects of anhydrous ammonia on fermentation of chopped, high-mo isture ear corn. J. Dairy Sci. 66:23432348. Allen, M.S., M. Oba, D. Storck, and J.F. Bec k. 1997. Effect of brown midrib 3 gene on forage quality and yield of corn hybrids. J. Dairy Sci. 80(Suppl. 1):157. (Abstr.) Andrae, J.G., C.W. Hunt, S.K. Duckett, L.R. Kennington, P. Feng, F.N. Owens, and S. Soderlund. 2000. Effect of high-oil corn on grow th performance, diet digestibility, and energy content of finishing diets fed to beef cattle. J. Anim. Sci. 78:2257-2262. Auerbach, H., E. Oldenburg, and F. Weissbach. 1998. Incidence of Penicillium roqueforti and roquefortine C in silages. J. Sci. Food Agric. 76:565-572. Avila, C.D., E.J. DePeters, H. Perez-Monti, S. J. Taylor, and R.A. Zi nn. 2000. Influences of saturation ratio of supplemental dietary fat on digestion and milk yield in dairy cows. J. Dairy Sci. 83:1505-1519. Bacon, C.W., and D.M. Hint on. 1996. Symptomless endophytic colonization of maize by Fusarium moniliforme. Can. J. Bot. 74:1195-1202. Bagg, J. 2001. Harvesting corn silage at the right moisture. Ontari o Ministry of Agriculture and Fd. Ext. Publ. August, 2001. Online. Available: http://www.omafra.gov.on.ca/english/ crops/facts/harvesting_corn.htm Accessed Jan. 12, 2005. Baker, T. 2002. Be on the lookout for hemorrhagic bowel syndrome. Hoards Dairyman. Page 776. November, 2002. Bal, M.A., J.G. Coors, and R.D. Shaver. 1997. Impact of the maturity of corn for use as silage in the diets of dairy cows on intake, dige stion, and milk produc tion. J. Dairy Sci. 80:2497-2503. Bal, M.A, R.D. Shaver, K.J. Shinners, and L.D. Satter. 1998. Effect of mechanical processing on the utilization of whole-plan t corn silage by lactating dairy cows. J. Anim. Sci. 76(Suppl. 1):334. (Abstr.)

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99 Bal, M.A, R.D. Shaver, H. Al-Jobeile, J.G. Coors, and J.G. Lauer. 2000. Corn silage hybrid effects on intake, digestion, and milk produc tion by dairy cows. J. Dairy Sci. 83:28492858. Ballard, C.S., E.D. Thomas, D.S. Tsang, P. Mandebvu, C.J. Sniffen, M.I. Endres, and M.P. Carter. 2000. Effect of corn silage hybrid on dry matter yield, nutrient composition, in vitro digestion, intake by dairy heifers, and milk production by dairy cows. J. Dairy Sci. 84:442-452. Barnett, A.J.G. 1954. Silage fermentation. Academic Press, New York. Barriere, Y., J.C. Emile, R. Traineau, and Y. Hebert. 1995. Genetic variation in the feeding efficiency of maize genotypes evaluated from experiments with dairy cows. Plant Breed. 114:144-148. Bastiman, B., and J.F.B. Altman. 1985. Losses at various stages in si lage making. Res. Dev. Agric. 2:19-25. Bekavac, G., M. Stojakovic, D. Jockovic, J. Bo canski and B. Purar. 1998. Path analysis of stay-green trait in maize. Cer. Res. Comm. 26:161-167. Bernard, J.K, J.W. West, D.S. Trammell, and G. H. Cross. 2004. Influence of corn variety and cutting height on nutritive value of silage fe d to lactating dairy cows. J. Dairy Sci. 87:2171-2176. Block, E., L.D. Muller, L.C. Griel, Jr., a nd D.L. Garwood. 1981. Brown midrib-3 corn silage and heat extruded soybeans fo r early lactating dairy cows J. Dairy Sci. 64:1813-1825. Bolsen, K. K., H. J. Ilg, and D. E. Axe. 1980 Additives for corn silage. J. Anim Sci. 51(Suppl 1):230. (Abstr.) Bolsen, K.K., A. Laytimi, and J. White. 1989. Effects of enzyme and inoculant additives on preservation of alfafa silage. J. Dairy Sci. 72(Suppl. 1):297. (Abstr.) Bolsen, K.K., D.R. Bonilla, G.L. Huck, M.A. Young, and R.A. Hart-Thakur. 1996. Effect of a propionic acid bacterial inocul ant on fermentation and aerobic stability of whole-plant corn silage. Kansas Agric. Exp. Stn. Prog. Rep. 756:77-80. Borras, L., G.A. Maddonni, and M.E. Otegui. 2 003. Leaf senescence in maize hybrids: plant population, row spacing and kernel set e ffects. Field Crops Res. 82:13-26. Borrell, A.K., and G.L. Hammer. 2000. Nitrogen dynamics and the physiological basis of staygreen in sorghum. Crop. Sci. 40:1295-1307.

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100 Borrell, A.K., and G.L. Hammer, and E.V. Oo steron. 2001. Stay-green: A consequence of the balance between supply and demand for nitr ogen during grain filling? Ann. Appl. Biol. 138:91-95. Britt, D.G., and J.T. Huber. 1975. Preservation of animal performance of high moisture corn treated with ammonia or propioni c acid. J. Dairy Sci. 59:668-674. Britt, D.G., J.T. Huber, and A.L. Rogers 1975. Fungal growth and acid production during fermentation and refermentation of organic acid treated corn silages. J. Dairy Sci. 58:532539. Buck, G.R., W.G. Merrill, C.E. Coppock, and S.T. Slack. 1969. Effect of recutting and plant maturity on kernel passage and feeding valu e of corn silage. J. Dairy Sci. 52:1617-1632. Casper, D.P., and D.J. Schingoethe. 1989. Mode l to describe and a lleviate milk protein depression in early lactation dairy cows fed a high fat diet J. Dairy Sci. 72:3327-3335. Cavalieri, A.J., and O.S. Smith. 1985. Grain fillin g and field drying of a set of maize hybrids released from 1930 to 1982. Crop Sci. 25:856-860. Chen, J., M.R. Stokes, and C.R. Wallace. 1994. Effect of enzyme-inoculant systems on preservation and nutritive value of haycrop and corn silage. J. Dairy Sci. 77:501-512. Cherney, J.H., D.J.R. Cherney, D.E. Akin, and J.D. Axtell. 1991. Potential of brown-midrib, low-lignin mutants for improving fo rage quality. Adv. Agron. 46:157-198. Clark, P.W., S. Kelm, and M.I. Endres. 2002. Effect of feeding a corn hybrid selected for leafiness as silage or grain to lacta ting dairy cattle. J. Dairy Sci. 85:607-612. Cleale, R.M., IV, J.L. Firkins, F. Van Der Bee k, J.H. Clark, E.H. Jaster, C.G. McCoy, and T.H. Klusmeyer. 1990. Effect of inoculation of whole plant corn forage with Pediococcus acidilactici and Lactobacillus xylosus on preservation of silage and heifer growth. J. Dairy Sci. 73:711-718. Cole, R.J., J.W. Kirksey, J.W. Dorner, D.M. W ilson, J. Johnson, D. Bedell, J.P. Springer, K.K. Chexal, J. Clardy, and R.H. Cox. 1977. Mycotoxins produced by Aspergillus fumigatus isolated from silage. Ann. Nutr. Aliment. 31:685-691. Colenbrander, V.F., V.L. Lechtenberg, and L.F. Bauman. 1973. Digestibility and feeding value of brown midrib corn silage. J. Anim. Sci. 37:294-295. Cooke, K.M., and J.K. Bernard. 2005. Effect of length of cut and kernel processing on use of corn silage by lactating dairy cows. J. Dairy Sci. 88:310-316. Coors, J.G., K.A. Albrecht, and E.J. Bures. 1997. Ear-fill effects on yiel d and quality of corn silage. Crop Sci. 37:243-247.

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101 Coulombe, J.J., and L. Favreau. 1963. A ne w simple semi micro method for colorimetric determination of urea. Clin. Chem. 9:102-108. Cox, W.J., and D.J.R. Cherney. 2001. Influence of brown midrib, leafy, and transgenic hybrids on corn forage production. Agron. J. 93:790-796. Crosbie, T.M. 1982. Changes in phy siological traits associated w ith long-term breeding efforts to improve grain yield of maize. Pages 206223 in H.D. Loden and D. Wilkin son (ed.) Proc. 37th Annu. Corn and Sorghum Ind. Res. Conf., Chicago, IL. 5-9 Dec. 1982. Am. Seed Trade Assoc. Washington, DC. Cummins, D.G., and R.E. Burns. 1969. Yield and quality of corn silage as influenced by harvest height. Agron. J. 61:468-470. Cummins, D.G. 1970. Quality and yield of corn plants and component parts when harvested for silage at different matu rity stages. Agron. J. 62:781-784. Curran, B., and Posch. 2001. Agronomic management of silage for yield and quality-silage cutting height. Crop Insights 10(2):1-4. Dado, R.G. 1999. Nutritional benefits of specialty corn grain hybrid in dairy diets. J. Anim. Sci. 77:197-207. Darby, H.M., and J.G. Lauer. 2002. Harvest date and hybrid influence on corn forage yield, quality, and preservati on. Agron. J. 94:559-566. Davies, J.H., and J.M. Wilkinson. 1993. Is the m ilk line score a useful indicator of the dry matter content of forage maize? Pages 1-5 in Proc. Ann.Conf. UK Maize Growers Assoc., Univ. Reading, United Kingdom. Daynard, T.B., and R.B. Hunter. 1975. Rela tionship among whole plant moisture, grain moisture, dry matter yield, and quality of w hole plant corn silage. Can. J. Plant Sci. 55:77-84. Dennison, A.C., D.C. VanMetre, R.J. Callan, P. Dinsmore, G.R. Mason, R.P. Ellis. 2002. Hemorrhagic Bowel Syndrome in dairy cattle : 22 cases (1997-2000). J. Am. Vet. Med. Assoc. Sep 1; 221(5):686-689. DePasquale, D.A., and T.J. Montville. 1990. Mechanism by which ammonium bicarbonate and ammonium sulfate inhibit mycotoxigenic fungi. Appl. Environ. Microbiol. 56:3711-3717. Dhiman, T.R., M.A. Bal, Z. Wu., V.R. Moreira, R.D. Shaver, L.D. Satter, K.J. Shinners, and R.P. Walgenbach. 2000. Influence of mechanical processing on utilization of corn silage by lactating dairy cows. J. Dairy Sci. 83:2521-2528.

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102 Dominguez, D.D., V.R. Moreira, and L.D. Satte r. 2002. Effect of feeding brown midrib corn silage or conventional corn silage cut at either 9 or 28 on milk yield and milk composition. Pages 98-99 in US. Dairy Fora ge Research Center 200-2001 Research Report, Madison, WI. D'Mello J.P.F., C.M. Placinta, and A.M.C. M acdonald. 1999. Fusarium myco toxins: a review of global implications for animal health, welfar e and productivity. Anim. Feed Sci. Technol. 80:183-205. Drackley, J.K. 1997. Update on high oil corn for dairy cattle. Pages 108-117 in Proc. 4-State Applied Nutrition and Management Confer ence. University Wisconsin, Madison, WI. Driehuis, F.S., and P.G. van Wikselaar. 1996. Eff ects of addition of formic, acetic or propionic acid to maize silage and low dry matter gras s silage on the microbial flora and aerobic stability. Pages 256-257 in D.I.H. Jones, R. Jones, R. Dewhurst, R. Merry, and P.M. Haigh (ed.) Proc. 11th Int. Silage Conference, Aberystwyth, UK. 8-11 September 1996. IGER, Aberystwyth, UK. Driehuis, F.S., J.W.H. Oude Elferink, and S.F. Spoelstra. 1999. Anaerobic lactic acid degradation during ensilage of w hole crop maize inoculated with Lactobacillus buchneri inhibits yeast growth and improve aerobic stability. J. Appl. Microbiol. 87:583-594. Duvick, D.N. 1997. What is yiel d? Pages 332-335 in G.O. Edm eades et al. (ed.) Developing drought and low N-tolerant maize. Proc of a Symp. 25-29 Mar. 1996. CIMMYT, El Batan, Mexico. Elliot, J.P., J.K. Drackley, D.J. Schauff, and E.H. Jaster. 1993. Diets containing high-oil corn and tallow for dairy cows during earl y lactation. J. Da iry Sci. 76:775-789. Ettle, T., and F.J. Schwarz. 2003. Effect of maize variety harvested at different maturity stages on feeding value and performance of dairy cows. Anim. Res. 52:337-349. Fakorede, M.A.B., and J.J. Mock. 1980 Growth analysis of maize variety hybrids obtained from two recurrent selection programme s for grain yield. New Phytol. 85:393-408. Fairey, N.A. 1983. Yield, quality and development of forage maize as influenced by dates of planting and harvesting. Can. J. Plant Sci. 63:157-168. Fernandez, I. and B. Michalet-Doreau. 2002. Eff ect of maturity stag e and chopping length of maize silage on particle size reduction in dairy cows. Anim. Res. 51:445-454. Fernandez, I., C. Martin, M. Champion, and B. Michalet-Doreau. 2004. Effect of corn hybrid and chop length of whole-plant corn silage on digestion and intake by dairy cows. J. Dairy Sci. 87:1298-1309.

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103 Flachowsky, G., W. Peyker, A. Schneider, and K. Henkel. 1993. Fibre analyses and in sacco degradability of plant fractions of two corn varieties harvested at various times. Anim. Feed Sci. Technol. 43:41-50. Forouzmand, M.A., G. R. Ghorbani and M. A likhani. 2005. Influence of hybrid and maturity on the nutritional value of corn silage for l actating dairy cows. I: Intake, milk production and component yield. Pakistan J. of Nutr. 4 (6):435-441. Frenchick, G.E., D.G. Johnson, J.M. Murphy, and D.E. Otterby. 1976. Brown midrib corn silage in dairy cattle rati ons. J. Dairy Sci. 59:2126-2129. Ganoe, K.H., and G.W. Roth. 1992. Kernel milk line as a harvest indicator for corn silage in Pennsylvania. J. Prod. Agric. 5:519-523. Giardini, A., F. Gaspari, M. V ecchiettini, and P. Schenoni. 1976. E ffect of maize silage harvest stage on yield, plant composition and fermen tation losses. Anim. Feed Sci. Technol. 1:313-326. Gochman, N., and J.M. Schmidz. 1972. Applicati on of a new peroxide indicator reaction to the specific, automated determination of glucos e with glucose oxidase. Clin. Chem. 18:943952. Goeger, D.E., R.T. Riley, J.W. Dorner, and R. J. Cole. 1988. Cyclopiazonic acid inhibition of the Ca2+-transport ATPase in rat skeletal musc le sarcoplasmic reticulum vesicles. Biochem. Pharmacol. Mar. 1; 37(5):978-981. Goering, H.K., and D.R. Waldo. 1980. Anhydrous a mmonia addition to whole corn plant for ensiling. J. Dairy Sci. 63(Suppl. 1):183. (Abstr.) Grummer, R.R. 1991. Effect of feed on the composition of milk fat. J. Dairy Sci. 74:32443257. Hammes, D.J. 1997. Developing markets for optimu m EG high oil corn. Pages 1-10 in Proc. Annu. III. Corn Breeders School, 33rd. Dept. Of Crop Sciences, Un iv. of Illinois, UrbanaChampaign, IL. Harrison, J.H., L. Johnson, R. Riley, S. Xu, K. Loney, C.W. Hunt, a nd D. Sapienza. 1996. Effect of harvest maturity of whole plant corn silage on milk production and component yield, and passage of corn grain and starch into feces. J. Dairy Sci. 79(Suppl. 1):149. (Abstr.) Havilah, E.J. and A.G. Kaiser. 1991. Milk line score as a guide to ha rvest time for forage maize in Australia. Pages 102-103 in Moran J.B. (ed.) Maize in Australia Food, Forage and Grain. Agric. Res. Inst. Ky abram, Victoria, Australia. Havilah, E.J. and A.G. Kaiser. 1994. The sta y-green characteristic and maize silage production. Proceedings of the Second Aust ralian Maize Conf. Gatton, Queensland.

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106 Kruczynska, H., K. Darul, W. Nowak, and I. Kowalik. 2001. The chemical composition and ruminal degradability of maize silages depe nding on the cultivar and mowing height at harvest. Anim. Feed Sci. Technol. 10(Suppl. 2):331-337. Kuehn, C.S., J.G. Linn, D.G. Johnson, H.G. Jung and M.I. Endres. 1999. Effect of feeding silages from corn hybrids selected for leafiness or grain to la ctating dairy cattle. J. Dairy Sci. 82:2746-2755. Kung, L. Jr., A.C. Sheperd, A.M. Smagala, K.M. Endres, C.A. Bessett, N.K. Ranjit, and J.L. Glancey. 1998. The effect of preservatives based on propionic acid on the fermentation and aerobic stability of corn silage and a to tal mixed ration. J. Dairy Sci. 81:1322-1330. Kung, L. Jr., J.R. Robinson, N.K. Ranjit, J.H. Chen, C.M. Golt, and J.D. Pesek. 2000. Microbial populations, fermentation end-products, and aerobi c stability of corn silage treated with ammonia or a propionic acid-base pr eservative. J. Dairy Sci. 83:1479-1486. Kung, L., and N.K. Ranjit. 2001. The effect of Lactobacillus buchneri and other additives on the fermentation and aerobic stability of ba rley silage. J. Dairy Sci. 84:1149-1155. Kung, L. Jr., C.C. Taylor, M.P. Lynch and J.M. Neylon. 2003. The effect of treating alfalfa with Lactobacillus buchneri 40788 on silage fermentation, aerob ic stability, and nutritive value for lactating dairy cows. J. Dairy Sci. 86:336-343. Lacey, J. 1989. Preand post-harvest ecology of fungi causing spoilage of foods and other stored products. J. Appl. Bacteriol. 67(Suppl.), 11S-25S. LaCount, D.W., J.K. Drackley, T.M. Cicela, a nd J.H. Clark. 1995. High oil corn as silage or grain for dairy cows during an entire lactation. J. Dair y Sci. 78:1745-1754. Lambert, R.J. 2001. High-oil hybrids. Pages 131154 in A.R. Hallauer (ed.) Specialty corns. CRC Press, Boca Raton, FL. Lauer, J. 1998. Corn kernel milk stage and silage harvest moisture in Proceedings of the 1998 Forage Symp. University of Wisconsin, Madison, WI. Leaver, J.D. 1975. The use of propionic acid as an additive for maize silage. J. Br. Grassl. Soc. 30:17-21. Lechtenberg, V.L., L.D. Muller, L.F. Ba uman, C.L. Rhykerd, and R.F. Barnes. 1972. Laboratory and in vitro eval uations or inbred and F2 populations of brown midrib mutants of Zea mays L Agron. J. 64:657-660. Lewis, A.L., W.J Cox, and J.H Cherney. 2004. Hybrid, maturity, and cutting height interactions on corn forage yiel d and quality. Agron. J. 96:267-274.

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113 Whitlock, L.A., D.J. Schingoethe, A.R. Hippen, K.F. Kalscheur, and A.A. AbuGhazaleh. 2003. Milk production and composition from cows fe d high oil or conven tional corn at two forage concentrations. J. Dairy Sci. 86:2428-2437. Wilkinson, J.M., and R.H. Phipps. 1979. The development of plant components and their effects on the composition of fresh and ensiled forage maize. 2. The effect of genotype, plant density and date of harvest on the co mposition of maize silage. J. Agric. Sci. 92:485-491. Wilkinson, J.M., G. Newman, and D.M. Alle n. 1998. Maize producing and feeding maize silage. Lincoln: Chalcombe Publications. Wilkinson, J. M., and J. Hill. 2003. Effect on yi eld and dry-matter distribution of the staygreen characteristics in cultivars of forage maize grown in England. Grass and Forage Science. 58:258-264. Williams, C.H., D.J. David, and O. Iismaa. 1962. The determination of chromic oxide in feces samples by atomic absorption spectrophot ometry. J. Agric. Sci 59:381-385. Williamson, D.H., J. Mellanby, and H.A. Krebs. 1962. Enzymatic determination of D (-) Bhydroxybutyric acid and acetoacetic acid in blood. Biochem. J. 228:727733. Wolfe, D.W., D.W. Henderson, T. C.Hsiao, and A. Alvino. 1988. Inte ractive water and nitrogen effects on senescence of maize. I. Leaf area duration. Agron. J. 80:859-864. Woodfin, C.A., D.T. Rosenow, and L.E. Clark. 19 88. Association between the stay-green trait and lodging resistance in sorghum. Page 102 in Agron. Abstr., ASA, Madison, WI. Woolford, M.K, K.K. Bolsen, and L.A. Peart. 1982. Studies on the aerobic deterioration of whole crop cereal silages. J. Agric. Sci. 98:529-535. Woolford, M.K. 1984. The Silage Fermentati on. Marcel Dekker, Inc., New York, NY. Xu, S., J. H. Harrison, W. Kezar, N. Entriki n, K.A. Loney, and R.E. Riley. 1995. Evaluation of yield, quality, and plant composition of early -maturing corn hybrids harvested at three stages of maturity. Prof. Anim. Sci. 11:157-165.

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114 BIOGRAPHICAL SKETCH Kathy Gisela Arriola was born on Septembe r 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 Moli na, Peru in 1998. While at the Agraria La Molina she earned pre-professional experience in the Investigation Prog ram 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 Univer sity 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 pr ojects related to her field. Ka thy was involved in the Animal Science Graduate Student Association and she was an active member of Gamma Sigma Delta.


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Title: Effect of Stay-Green Ranking, Maturity, and Moisture Concentration of Corn Hybrids on Silage Quality and the Health and Productivity of Lactating Dairy Cows
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Copyright Date: 2008

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Table of Contents
    Title Page
        Page 1
        Page 2
    Dedication
        Page 3
    Acknowledgement
        Page 4
    Table of Contents
        Page 5
        Page 6
    List of Tables
        Page 7
    List of Figures
        Page 8
    Abstract
        Page 9
        Page 10
    Introduction
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    Literature review
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    Effect of maturity at harvest of corn hybrids differing in stay-green ranking on the quality of corn silage
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    Effect of stay-green ranking, maturity and moisture concentration of corn silage on the health and productivity of lactating dairy cows
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    General summary
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    References
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Full Text





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

































Copyright 2006

by

Kathy Gisela Arriola

































To my adorable son Wilhelm Andre.









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.









TABLE OF CONTENTS



A C K N O W L E D G M E N T S ..............................................................................................................4

L IST O F T A B L E S ......................................................................................................... ........ .. 7

LIST OF FIGURES ............................................. .. .......... ............ ...............8

A B S T R A C T .................................................................................................................... ......... .. 9

CHAPTER


1 INTRODUCTION .................................. .. ........... ............................. 11

2 L ITE R A TU R E R E V IE W .............. ..................................................................... 13

Factors Affecting the Nutritive Value of Corn Plants .......................................................13
Hybrid ................................................. ............ .... ..................... 13
B row n m idrib hy b rid s ............................................................................ ............... 14
Grain digestibility (flint vs. dent hybrids).......................................................... 14
H ig h -o il h y b rid s ....................................................................................................... 17
High-grain yield and leafy hybrids.....................................................20
C u ttin g H eig h t ................................................................................................................ 2 1
M atu rity ......................................................................................................... ....... .. 2 4
D ig e stib ility .............................................................................................................. 2 7
A nim al perform ance ............................................. .. ...................... .. .. ............... 28
Factors Affecting the Fermentation of Corn Silage...........................................................29
M a tu rity ........................................................................................................................... 3 0
In o cu lan ts ...................................................................................................... ........ .. 3 0
C h o p L e n g th .................................................................................................................. .. 3 2
P ro cessin g ....................................................................................................... ........ .. 3 2
C h em ical A d ditiv es ................................................................................................. 3 3
Factors Affecting Aerobic Stability of Corn Silage ..........................................................33
Y e a sts ............................................................................................................. ........ .. 3 3
Molds and Mycotoxins ............................... .... ......... ...... ............... 34
Microbial Inoculants....................... .. ........... ...............................36
A m m on ia ...................................................................................................... ....... .. 3 8
H em orrhagic B ow el Syndrom e .. .................................................................... ................ 39
V ariable M anure Syndrom e.................................................. ............................................ 40
Stay-green C orn H ybrids ............... .. .................. .................. .......................... .................4 1

3 EFFECT OF MATURITY AT HARVEST OF CORN HYBRIDS DIFFERING IN
STAY-GREEN RANKING ON THE QUALITY OF CORN SILAGE ................................46









Introduction ........................................................ .................. 46
M materials and M methods .............. .............................................................................. 47
P lo t T ria l ............................................ ..................................................... ...............4 7
P planting and establish ent........................................ ....................... ................ 47
Fractionation and ensiling. ................ ............................................................ 48
Chemical analysis ..... ............... .. ........... .....................................48
S tatistic al A n aly sis ..........................................................................................................5 0
R results and D 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
Ferm entation Indices of Corn Silage Sam ples ........................................... ................ 54
C o n clu sio n s............................................................................................................. ........ .. 5 5

4 EFFECT OF STAY-GREEN RANKING, MATURITY AND MOISTURE
CONCENTRATION OF CORN SILAGE ON THE HEALTH AND PRODUCTIVITY
O F L A C TA TIN G D A IR Y C O W S .........................................................................................67

Introduction ........................................................ .................. 67
M materials and M methods .............. .............................................................................. 68
Diets ................................. ......................... ....... ..................... 69
Sam ple C collection and A nalysis.................................... ....................... ................ 69
S tatistic al A n aly sis ..........................................................................................................7 2
R results and D iscu ssion .................................................... ............................................... 73
Chem ical Com position of Corn Silage....................................................... ................ 73
V voluntary Intake ......................................................................................................... 74
M ilk Production and C om position ..................................... ..................... ................ 75
Body W eight and Plasm a M etabolites ....................... ............................................ 77
Rum en Param eters and H health Indices....................................................... ................ 77
Conclusions ..................................................... .................. 79

5 G E N E R A L SU M M A R Y .................................................... .............................................. 94

L IST O F R EFE R E N C E S ............................................................................................. 98

B IO G R A PH IC A L SK E T C H .................................................... ............................................. 114














6









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, m aturity and source ...................................... ...................... ................ 60

3-3 Chemical composition of unensiled ears from corn hybrids differing in stay-green
(SG ) ranking, m aturity and source ...................................... ...................... ................ 62

3-4 Chemical composition of corn silages made from hybrids differing in stay-green
(SG ) ranking, m aturity and source ...................................... ...................... ................ 63

3-5 Fermentation indices of corn silages silages made from hybrids differing in stay-
green (SG ) ranking, m aturity 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
treatm ent 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
c o w s ........................................................................................................ ........ . ....... 8 4

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
c o w s ........................................................................................................ ........ . ....... 8 6









LIST OF FIGURES


Figure page

4-1 Effect of maturity at harvest and moisture addition to corn silages with contrasting
stay-green rankings on rum inal 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









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.









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.









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









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.









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









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.









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









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









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









(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









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.









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-F 1 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 TMF 106, 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.









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









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 1 Ig 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.









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









(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 12 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 12 ML to black layer (BL). As kernel

fill increased from % 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 % ML stage to the BL stage.









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.









Whole plant fiber concentration generally declined from soft dough to 12 ML and then plateaued

after 1/ ML. Decreases in whole plant fiber concentration from soft dough to 1/ 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









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 parking 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.









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









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 12 and % 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 23 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 maj or 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 1/2 to 23

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









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) ML, 28.5% DM, and 3) % ML, 27.9% DM. In a second experiment at 1/

ML, 27.1% DM, 2/% 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 1/3 to 2/3 ML and 23% 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









(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.









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.









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 H20 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),









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 Aspergillusfumigatus, 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









of dairy herd health problems during years with near ideal growing conditions and record corn

yields (Rankin and Grau, 2004).

Two species of Aspergillus, Aspergillusflavus and A. fumigatus and/or their mycotoxins,

are reported regularly in silages. Aspergillusflavus 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









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.









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 ofL. 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 Ixl06 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









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,









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 Clostridiumperfringens 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









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.

Aspergillusfumigatus 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 Aspergillusfumigatus 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.









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,









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









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,









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









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.









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









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 1/ and % kernel

milk line. Such results led to the widely held notion that corn intended for ensiling should be

harvested at the 12 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.









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 (105C

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 (25C) 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 550C 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









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 2C

rise in silage temperature above ambient temperature (23C). Silage DM concentration was

determined at 60C in a forced air oven for 48 h. Ash concentration was determined in a muffle

furnace at 550C 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 4C and 21,500 x g for 20

min and the supernatant was frozen (-20C) 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









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 = + Ci + SGj + Mk + B + Eijkl

where

[t = 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









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.









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









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).









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









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.









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









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.










Table 3-1. Yield and chemical composition of unensiled whole plants from corn hybrids differing in stay-green (SG) ranking,
maturity and source.


Maturity1 High SG
PN31Y43 CPL827
1 17.1 18.4
2 15.9 13.8
3 13.4 17.7


Average SG
PN32D99 CPL799
15.1 13.1
16.3 12.9
17.8 22.9


SE SG Maturity
(m)
1.5 ns 0.016, Q


IP value


Source'
(c)
ns


SG*m SG*c m*c SG*m*c

0.002 ns 0.005 ns


18.3 ns <.001, L ns ns 0.05 0.01



2.4 ns 0.009, Q 0.012 ns ns 0.05


206 19.7 ns <.001, L ns ns 0.001 0.001 ns
355
297

127 8.9 0.003 ns ns ns 0.08 0.001 0.032


CP, 1 99 92
g/kg DM 2 86 86
3 83 66
ns = not significant, P > 0.10; L


1 Maturity 1, 2 and 3


94 6.7 ns 0.001, L ns ns ns ns ns


Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05


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


Yield,
(t/ha)


DM,
g/kg


Ash,
g/kg DM


Starch,
g/kg DM


WSC3,
g/kg DM










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:; = Quadratic effect. P < 0.05


' 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









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
' Maturity 1, 2 and 3 = 25, 32 and 37 g DM/lOOg 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










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









Table 3-3. Chemical composition of unensiled ears from corn hybrids differing in stay-green (SG) ranking, maturity and source.

P value
Maturity' 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,
' Maturity 1, 2 and 3


P > 0.10; L
= 25, 32 and


= Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
37 g DM/lOOg 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











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,
' Maturity 1, 2 and 3


P > 0.10; L
= 25, 32 and


= Linear effect, P < 0.05; Q = Quadratic effect, P < 0.05
37 g DM/lOOg 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










Table 3-4. Continued


Maturity1 High SG


PN31Y43
111
96


CPL827
104
90


Average SG
PN32D99 CPL799
100 98
88 89


SE SG Maturity
(m)
5.6 0.086 <.001,L


P value
Source2 SG*m SG*c m*c


(c)
ns


SG*m*c


ns ns ns ns


88 84


474 14.8 0.068 <.001, L 0.034
382
370

257 8.5 0.082 <.001, L 0.002


ns <.001 ns




ns <.001 ns


IVDMD, 1
g/kg DM 2
3
ns = not significant,
' Maturity 1, 2 and 3


610
640
631
P > 0.10; L


Linear effect


660
617
605
P < 0.05;


25, 32 and 37 g DM/100g at harvest, respectively.


22.9 0.070 ns ns ns 0.07 ns


654
Q = Quadratic effect, P < 0.05


2 Source = Pioneer (PN) Hi-Bred International, Des Moines, Iowa and Croplan (CPL)Genetics, St. Paul, MN


CP,
g/kg DM



NDF,
g/kg DM



ADF,
g/kg DM










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


3.7 3.8
3.8 3.8


8.7 ns 0.02, Q 0.114


76.5
58.4
43.0

44.9
30.9
22.6


73.1
46.2
47.0

43.1
24.4
24.5


63.7
56.5
56.8

39.1
28.3
30.9


86.5
50.8
45.9

51.2
25.5
28.8


7.7 ns <.001, L




4.7 ns <.001, L


ns ns ns 0.03


ns ns ns ns ns




ns ns ns ns ns


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
' 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


3.8 3.8
3.8 3.7


NH3-N,
g/kg
Total N


Lactic acid,
g/kg DM



Acetic acid,
g/kg DM










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:; = Quadratic effect. P < 0.05


' 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









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 (1/3 to 23 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









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









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 1 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









during each week in the last 14 d of each period, preserved with potassium dichromate and stored

at 4C. 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 -20C. 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 (Cr203) 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 60C 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









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 composite, 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 2C rise in silage temperature above ambient temperature (23C).

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









were centrifuged at 12,000 x g for 20 min, after which the supernatant was collected and frozen (-

20C) 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 45C.

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 = + Ti + Pj + Ck + R + Eijkl

where

i: general mean

Ti: treatment effect (fixed effect)

Pj: period effect (fixed)

Ck: cow effect (random effect)

RI: residual effect

Eijkj: experimental error

The model used for analyzing rumen VFA and ammonia-N data in Experiment 2 was

Yijk = + Ti+ Pj + Hk + C + Eijkl

where

i: general mean









Ti: treatment effect (fixed effect)

Pj: period effect (fixed)

Hk: time effect (repeated measurement)

Ci: cow effect (random effect)

Eijkj: 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 atP < 0.05 and tendencies atP < 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.









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 (1 milk line; ML) or 30.5% DM

(23 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









(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.









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 (14 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.









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 C), 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.









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









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/lOOg 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/lOOg 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









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.










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
00
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/lOOg 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









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 cfu/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
00 Maturity 1 = 26 g DM/100g at harvest, Maturity 2 = 35 g DM/100g at harvest
S 1 LSG = Low stay-green hybrid
2 HSG = High stay-green hybrid
3 HSG (wet) = HSG hybrid wetted with 15 1 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 > 2C.









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 MOIST
Intake, 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/lOOg
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 1 of water/ton of forage at ensiling









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 MOIST
Milk, 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
00 2
2 HSG = High stay-green hybrid
3 HSG (wet) = HSG hybrid wetted with 15 1 of water/ton of forage at ensiling









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 MOIST


BW, kg 628 638 638 634 636
BW gain, kg/d 0.30 0.61 0.74 0.62 0.80
Plasma BUN, mg/dl 19.4 19.4 19.1 18.8 19.7
Plasma glucose, mg/dl 64.4 66.1 66.6 66.9 66.9
P3-Hydroxybutyrate, mmol/1 0.25 0.29 0.29 0.27 0.26
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 1 of water/ ton of forage at ensiling


14.0
0.11
0.8
1.0
0.03


ns ns ns
0.03 0.03 ns
ns ns ns
ns 0.09 ns
ns ns ns









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 MOIST
Rectal 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
NH3-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
S 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
1LSG = Low stay-green hybrid
2 HSG = High stay-green hybrid
3 HSG (wet) = HSG hybrid wetted with 15 1 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














6.5
6h-- LSG Mat 1
--0- HSGMat 1
S6 ---HSG Mat 2
A LSG Mat2
5.5-o- HS G(wet) Mat 1
5.5


5
0 2 4 6 8 10 12
Time after feeding, h


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.










48

42
36 --LSGMat 1

23 --o- HSG Mat 1

S24 -- HSGMat 2
S18 --LSGMat2
12
-o- HSG(wet) Mat 1
6

0
0 2 4 6 8 10 12
Time after feeding, h


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 DMI100g at harvest, Mat 2 = 35 g DMI100g at
harvest.












60

S58 --LSGMat 1

56 -o-HSGMat 1
-m-HSGMat2
S54
54 -A-LSGMat2
o 52 -o- HSG(wet) Mat 1

50

48
0 2 4 6 8 10 12
Time after feeding, h


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.














22 -A-LSGMat 1
20 -- HSG Mat 1
--- HSG Mat 2
18 LSGMat2
-o-- HSG(wet) Mat 1
16


14
0 2 4 6 8 10 12
Time after feeding, h


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 DMI100g at harvest, Mat 2 = 35 g
DM/100g at harvest.














-LSGMat 1
E 12 -- HSG Mat 1
-HSG Mat 2
11 --LSGMat 2
-o-- HSG(wet) Mat 1
10


9
0 2 4 6 8 10 12
Time after feeding, h


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.












3.4

3.2
LSGMat 1
.0 3
3 HSG Mat 1
2.8 -m- HSG Mat 2
2.6 -A-LSGMat2
-o0- HSG(wet) Mat 1
2.4

2.2

2
0 2 4 6 8 10 12
Time after feeding, h


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.










180


160 A

140 ---- LSGMat 1

120 --HSG Mat 1
S7 --- HSG Mat 2
S100 --LSGMat2
S80 -- HSG(wet) Mat 1

60 -

40
0 2 4 6 8 10 12
Time after feeding, h


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.









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 20-1 mini silos and sealed. Silos were stored for at least 107 d at ambient

temperature (25C) in a covered barn.









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 1 of water per ton of silage to forage harvested at Maturity 1









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/lOOg (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.









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.









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