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* Department of Animal Science, University of Minnesota, St. Paul, MN 55108
West Central Research and Outreach Center, University of Minnesota, Morris, MN 56267
USDA-Agriculture Research Service, St. Paul, MN 55108
Corresponding author: J. G. Linn; e-mail: linnx002{at}umn.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: corn silage hybrid • dairy cow • nutrient digestibility
Abbreviation key: COV = covariate corn silage, EE = ether extract, IVTD = in vitro true digestibility, IVNDFD = in vitro NDF digestibility, NDICP = neutral detergent insoluble CP
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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There are numerous lactation studies comparing different corn silage hybrids (Barriere et al., 1995; Oba and Allen, 1999; Kuehn et al., 1999; Bal et al., 2000; Ballard et al., 2001; Thomas et al., 2001; Clark et al., 2002). Of the available corn silage hybrid types, the brown midrib trait is the only one that consistently shows an improvement in milk production (Oba and Allen, 1999; Bal et al., 2000; Ballard et al., 2001). Several studies have reported small or no differences in milk production when leafy corn silage hybrids were fed to lactating dairy cows (Kuehn et al., 1999; Bal et al., 2000; Ballard et al., 2001). However, two studies (Thomas et al., 2001; Clark et al., 2002) have reported significant increases in milk production from feeding leafy corn silage hybrids compared with conventional corn silage hybrids to lactating dairy cows. Inclusion of leafy corn silage hybrids in dairy cattle diets often has not increased DMI over diets containing conventional corn hybrids (Kuehn et al., 1999; Bal et al., 2000; Thomas et al., 2001); however, Ballard et al. (2001) did find that Holstein heifers ate more of a leafy corn silage hybrid than a conventional hybrid, and Clark et al. (2002) observed higher DMI by midlactation Holstein cows fed diets containing a leafy corn silage hybrid than those fed diets containing conventional corn silage hybrids.
Although previous research has not shown a consistent increase in milk production or DMI from feeding a leafy corn silage hybrid, new and/or improved corn silage hybrids are introduced to the market each year. As new hybrids are developed, it is important to evaluate their agronomic traits and to determine the effects of new hybrids on dairy cattle performance. Mycogen Seeds (Dow AgroSciences, Indianapolis, IN) developed a new leafy corn silage hybrid, TMF2450, which they reported was selected for both increased NDF and starch digestibility. The objective of this study was to evaluate this new leafy corn hybrid against a conventional corn hybrid and an earlier generation leafy corn hybrid for nutrient composition and digestibility and DMI and lactation performance of dairy cows.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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A target of 33 to 35% whole plant DM and a kernel maturity of half milkline were set as targets for harvesting. However, actual kernel maturity was two thirds to full milkline when the corn silage hybrids reached the correct whole plant moisture levels. Corn silage hybrids were harvested on September 7, 8, and 11, 2000 (36F30, TMF2404, and TMF2450, respectively). The corn silages were harvested with a conventional forage harvester, without a kernel processor at a 0.95-cm theoretical length of cut. Yields for each of the corn silage hybrids were estimated by averaging the weights of individual wagonloads from measured areas of the field. Silages were fermented for a minimum of 35 d in 2.35-m diameter plastic silage bags (Ag-Bag, Int., Warrenton, OR) before the start of the feeding study.
Six plants from each hybrid were randomly selected from the fields before harvest. The plants were separated into three fractions: grain, stover, and cob plus husk. The individual plant parts were dried at 60°C in a forced-air oven to determine DM percentage and grain-to-stover ratios for each hybrid. Nutrient composition of the three corn silages was estimated for diet formulation with mini-silos. Mini-silos constructed of polyvinyl chloride pipe (10 cm in diameter by 35.5 cm tall) were packed with chopped whole corn plant material using a mechanical press and sealed on each end with a rubber cap and clamp. Gas was vented from the mini-silos via a small hole in one of the rubber caps that was fitted with a glass tube sealed with a slit rubber stopper. Six mini-silos were prepared for each hybrid from randomly collected samples of chopped silage throughout the harvest. Each silo contained approximately 2.2 kg of wet silage. Silos were allowed to ferment for 28 d before opening and compositing by hybrid. A sample from the mini-silo composite for each corn silage hybrid was analyzed by near infrared spectroscopy (Dairyland Laboratories, St. Cloud, MN) to determine nutrient composition for formulation of diets fed in the lactation study. Subsamples from the mini-silo composites were also tested for in situ starch digestibility using a rumen-fistulated cow fed a corn silage based TMR. Fifteen grams of corn silage (DM) was placed, without drying or grinding, into polyester in situ bags (25 x 35 cm). Bags were placed in the cow at 1200 h, approximately 8 h after feeding, and incubated for 16 h. Blank bags were included to correct for influx of starch into sample bags. Bags and residue were thoroughly washed by hand and dried in a 60°C forced air oven. The residue was then ground through a 1-mm cyclone mill (Udy Co., Fort Collins, CO) and analyzed for starch as described below.
Lactation Study
Cows and diets.
The lactation study was conducted from September 25, 2000, through July 15, 2001, at the West Central Research and Outreach Center, Morris, Minnesota. All cows were managed and cared for according to University of Minnesota Institutional Animal Care and Usage Committee recommendations (Animal Subjects Code 0010A69761). Multiparous Holstein cows were housed in a tie-stall barn and placed on a covariate diet immediately after parturition (Table 1
). Cows remained on the covariate diet for 21 d, after which they were assigned to one of three dietary treatments if they were healthy and producing an average of 25 kg/d or more of milk the last 3 d of the covariate period. Animals were blocked into groups of three by calving date and randomly assigned to corn silage treatments within calving date blocks. They remained on their respective treatments for 120 d. Fifty-two of the initial 60 cows assigned to dietary treatments completed the study. During the course of the study, two cows were removed from the 36F30 treatment due to Johne’s disease and death, two cows were removed from the TMF2450 treatment because of toxic mastitis and lameness, and four cows were removed from the TMF2404 treatment because of hardware disease, stifle injury, or death. Cows were milked at 0600 and 1800 h each day. Milk weights, feed intakes, and health information were recorded daily. Body weight and BCS (scale of 1 to 5 where 1 = thin to 5 = fat, Wildman et al., 1982) were taken every 2 wk. Milk samples were taken from the a.m. and p.m. milking on 1 d, every 2 wk, and analyzed for fat, true protein, and SCC (Stearns DHIA, Sauk Center, MN).
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, and composition of the grain mix is presented in Table 2. The covariate TMR contained a mixture of corn silage hybrids routinely fed at the West Central Research and Outreach Center, with other ingredients similar to those used in the experimental diets. Feed samples, orts, and TMR samples were taken on a weekly basis. Ingredient samples were checked for DM on a weekly basis, and diets were adjusted to maintain ingredients at constant percentages of the diet DM. Individual feed ingredient samples were composited every 4 wk, and subsamples were used for analysis of nutrient content. Total mixed ration and ort samples were composited every 4 wk and subsamples taken for nutrient analysis and particle sizing using a Penn State Particle Separator (NASCO; Fort Atkinson, WI) with two screens, sizes 0.79 and 1.91 cm. Smaller material passed through the screens to the collection pan.
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-amylase were included in the neutral detergent extraction, and heat stable -amylase was also added during the first two rinses (Hintz and Mertens, 1996). Acid detergent lignin was determined by digesting the ADF residue in 72% sulfuric acid (Hintz and Mertens, 1996). Samples were analyzed for ash in a muffle furnace at 500°C (AOAC, 1995). Monthly composites were analyzed for CP (NA 2100 Protein Nitrogen Analyzer, ThermoQuest Italia S. p. A., Italy; AOAC, 1995) and ether extract (EE; AOAC, 1995). Neutral detergent insoluble CP (NDICP) was determined after NDF extraction by analyzing the residue for CP. Because sodium sulfite was included in the neutral detergent solution, the NDICP concentration underestimated fiber-bound CP (Van Soest et al., 1991; Licitra et al., 1996), but NDICP was utilized in the calculation of NFC concentration. Starch was determined on feed, orts, and feces. Starch was hydrolyzed with -amylase (Sigma #A 3306; Sigma Chemical Co., St. Louis, MO) and amyloglucosidase (Sigma #A 3514). Glucose was assayed using a glucose oxidase kit (Sigma 510-A) using a plate reader at 450 nm. The NFC concentration was calculated using the following equation:
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Lactic acid and VFA concentrations of the silages and haylage were determined by GLC (Erwin et al., 1961).
In vitro true (IVTD) and NDF (IVNDFD) digestibilities of the monthly composite samples of haylage and treatment corn silages were determined after 48-h incubations with rumen fluid using the ANKOM DAISYII Incubator. Approximately 0.5 g of sample was weighed into ANKOM nylon bags (4.5 x 5.0 cm, 57-µm pore size) and heat sealed. Samples were presoaked in a mixture of McDougall’s buffer (McDougall, 1948) and porcine amylase (Sigma A-3176) for 24 h to improve repeatability of the IVNDFD measurements by removing starch prior to rumen fluid addition. Samples were subsequently incubated in a mixture of McDougall’s buffer and rumen fluid prepared in a 4:1 ratio, with the reducing agents L-cysteine hydrochloride hydrate and sodium sulfite added to the buffer solution. The rumen fluid was collected from a lactating Holstein cow fed a corn silage based TMR and strained through cheesecloth. After 48 h, bags were removed from the rumen fluid and rinsed. The samples were analyzed for NDF by the methods previously described.
The total digestible nutrients at maintenance intake (TDN1x) for haylage and corn silages were determined using nutrient analysis data and equations listed in the most recent Dairy NRC (2001). The IVNDFD means were used in the TDN1x calculations for each corn silage. The TDN1x and NEL at actual observed DMI were determined for the covariate and corn silage treatment diets using the most recent Dairy NRC model (2001).
Digestibility Study
In March 2001, digestibility of the corn silage diets used in the lactation study was determined. Fifteen cows from each dietary treatment were selected by DIM (ranging from 32 to 179 DIM) to obtain a 107-d average for each treatment. Because calving occurred over a 5-mo period, a few cows on each treatment had completed the lactation study but were retained on their respective dietary treatment for inclusion in the digestion study. Samples of the TMR from each dietary treatment were taken for 4 consecutive days. Orts from each cow were sampled 1 d after starting the TMR sampling and continued for 4 d. Individual daily ort samples were proportionately composited based on daily ort proportions relative to the 4-d total orts. Starting on d 3 of TMR sample collection, fecal samples were collected over a 3-d period every 6 to 8 h to provide 12 fecal samples per cow. Individual cow fecal samples were composited on an equal weight basis and frozen for future analysis. The composite TMR, orts, and fecal samples were dried in a 60°C forced-air oven and ground in a Wiley mill to pass through a 1-mm screen. Samples were subsequently analyzed for NDF, CP, and starch and for acid insoluble ash, which was used as an internal marker to determine apparent total-tract DM digestibilities (Van Keulen and Young, 1977).
Statistical Analysis
Milk production and composition, and feed intake data from the lactation study were analyzed as a randomized complete block design with three corn silage dietary treatments and 20 replicates. Cows were blocked according to calving date. Individual cow data from the covariate period of the study was included in the model. Data from the digestibility study were analyzed as a completely randomized design with the three dietary treatments and 15 replicates. Covariate period data were not included as a model parameter for the digestibility study. The least significant difference method was utilized to compare treatment means when the ANOVA F test was significant. All results are reported as least squares means. Differences among observations were considered significant at P < 0.05. The procedures in SAS were used for all statistical analyses (SAS, 1999).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). Grain DM percent was similar for all three hybrids at harvest (57.2 to 59.5% DM). Stalk, leaves, and tassel portions were 8 to 10 percentage units higher for TMF2450, resulting in numerically higher whole plant DM (35.7%) compared with 36F30 and TMF2404 (33.6 and 31.0%, respectively). In situ starch digestibility determined from the mini-silo samples was numerically higher for TMF2450, with approximately 4 percentage units more starch digested than TMF2404 and 8 percentage units more than 36F30 (86.2, 82.4, and 78.1%, respectively).
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. The TDN1x for 36F30, TMF2450, and TMF2404 was almost identical at 70 to 71%, which would be expected as nutrient content of the three corn silages was very similar. Although 36F30 is a conventional hybrid and would be expected to be higher in grain and lower in fiber than leafy hybrids, it contained the same amount of NDF (39%, DM basis) as the two leafy hybrids. The ADF content of all corn silages was nearly identical (20.2 to 21.5%). However, lignin content was 0.3 percentage units higher for TMF2450 than for 36F30 and TMF2404. Starch percentage did not differ among the corn silage hybrids. There were no differences in EE among the three corn silage hybrids.
In vitro true digestibility and IVNDFD for the three treatment corn silages are shown in Table 3. The IVTD tended (P < 0.10) to be higher (2 percentage units) for TMF2404 than 36F30 and TMF2450. The trend towards increased IVTD of TMF2404 reflects its possibly more digestible NDF fraction with TMF2404 being numerically 3.3 and 4.8 percentage units higher in IVNDFD than TMF2450 and 36F30, respectively; however, these numerical differences for IVNDFD were not significant. In a study by Thomas et al. (2001), even greater variation for in vitro digestibility (4.2 percentage units IVTD and 9.6 percentage units IVNDFD) was found between conventional and leafy corn silage hybrids.
Diet DM concentration was similar across all diets and averaged 51.3% (Table 4). The production NEL, based on actual average DMI (4.1 x maintenance) for the lactation study (Table 4), was similar for the three corn silage diets and averaged 1.56 Mcal/kg DM. The NDF from forage in the 36F30, TMF2450, and TMF2404 diets ranged from 20.3 to 22.1%. Total NDF, and NDF from forage and ADF concentrations in the diets were at or below the initial formulation levels, but above 2001 Dairy NRC recommendations (2001). These deviations in fiber levels may have resulted from the formulation being based on mini-silo samples, analyzed by near-infrared spectroscopy, compared with the monthly silage feed samples collected during the lactation trial and analyzed by wet chemistry. Concentrations of NDF, ADF, lignin, ash, EE, and starch were similar across diets.
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Intakes of DM, CP, and NDF were not different across the three corn silage diets (Table 5). Similarly, neither Kuehn et al. (1999) or Thomas et al. (2001) observed differences in DMI between diets containing conventional and leafy hybrids. In contrast, Clark et al. (2002) reported 0.9 kg/d higher DMI for diets containing a leafy corn silage hybrid as opposed to a conventional hybrid.
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. There was no difference in milk yield of cows fed the three corn silage diets. Lactation curves were similar for all corn hybrids (data not shown). Kuehn et al. (1999) and Ballard et al. (2001) also reported no difference in milk yields when leafy and conventional corn silage hybrids were fed to lactating cows. In contrast, cows fed diets containing leafy corn silage hybrids produced 1.5 and 1.4 kg/d more milk than cows fed conventional hybrids in two other studies (Thomas et al., 2001; Clark et al., 2002). Milk fat and protein yields were not different among treatments, ranging from 1.24 to 1.36 kg/d for milk fat and 1.01 to 1.12 kg/d for true milk protein. Clark et al. (2002) reported a 0.05 kg/d increase in milk fat production for cows fed a leafy corn silage diet compared with a diet containing conventional corn silage. In contrast, Thomas et al. (2001) reported a trend toward greater protein yield from cows fed a leafy corn silage diet. Yields of 4.0% FCM were not different at 35.4, 32.7, and 33.5 kg/d for 36F30, TMF2450, and TMF2404, respectively. Other studies have also reported no improvement (Kuehn et al., 1999; Bal et al., 2000; Ballard et al., 2001) in FCM production from feeding leafy corn silage hybrids, whereas two studies did find an increase in FCM (Thomas et al., 2001; Clark et al., 2002). Milk SCC were similar among treatment groups (data not shown). Cows fed 36F30, TMF2450, and TMF2404 had an average BW of 592, 589, and 613 kg, respectively, throughout the lactation study. The average weekly change in BW over the 17-wk lactation study for cows fed TMF2450 and 36F30 diets was -0.50 kg/wk, whereas cows fed TMF2404 diets had a small positive average BW gain. Cows fed 36F30, TMF2450, and TMF2404 diets all had normal BW curves, with small decreases in BW occurring in early lactation followed by slow gains throughout the rest of the study. The average BCS of cows was 2.87, and no treatment differences were found.
Digestibility Study
Milk yield and DMI of cows fed the three corn silage diets were not different during the digestibility study (Table 6), as was expected from the similar milk yield and DMI results during the lactation study. The similarity in DMI and diet compositions resulted in similar intakes of CP, NDF, and starch (Table 6). Apparent DM digestibility was lower for the TMF2404 diet than 36F30 or TMF2450 diets. Crude protein and NDF digestibilities were highest for the TMF2450 diet, intermediate for the 36F30 diet, and lowest for the TMF2404 diet. Because feed intake was not different among the three corn silage diets, we assume that rates of digesta passage were similar among treatments, and differences in rumen or lower gut retention times probably did not account for the observed changes in digestibility among the experimental diets. Differences among the corn silage diets for nutrient digestibilities may have resulted from intrinsic differences among the corn silages or associative effects related to the small differences among diets for ingredient proportions. The higher apparent NDF digestibility of the TMF2450 diet did not coincide with the corn silage IVNDFD data (Table 3) because TMF2450 corn silage IVNDFD was not significantly different compared with 36F30 and TMF2404. However, the TMF2450 diet contained less alfalfa haylage and more distillers grains than the other two diets. This diet composition probably resulted in the substitution of less digestible fiber from haylage for more digestible fiber from distillers grains. Apparent total-tract starch digestibility was not different between treatments and averaged 97.8% (Table 6). The numerically lower in situ 16-h starch digestibility for 36F30 (78.1%) compared with TMF2450 (86.2%) and TMF2404 (82.4%) mini-silo corn silages may indicate that rumen retention times were sufficiently long for the high-grain hybrid to reach the same extent of digestion as the leafy hybrids, or that intestinal digestion compensated for lower ruminal starch digestion of 36F30. In contrast, Bal et al. (2000) observed improved in vivo total-tract starch digestibility for a leafy corn silage containing diet.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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2 Current address: Washington State University, Puyallup, 7612 Pioneer Way, Puyallup, WA 98372; tnennich{at}wsu.edu.
Received for publication November 25, 2002. Accepted for publication April 3, 2003.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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