Location: Dairy Forage Research2009 Annual Report
1a. Objectives (from AD-416)
1) Identify and measure plant chemical and physical characteristics and dietary interactions that may alter nutrient digestibility and excretion by lactating dairy cattle. 2) Determine the effects of level of intake and digestion kinetics on diet component digestibility with current industry-representative lactating cows. 3) Measure the impact of fermentative digestion on nutrient utilization, quantify the transformations of nutrients into end-products of fermentation, and use molecular techniques to characterize and quantify changes in populations of ruminal bacterial species as affected by diet and animal. 4) Develop an integrated system for evaluating forage genotypes and validate the usefulness of in vitro, in situ, and small ruminant digestibility in assessing the utilization of nutrients by lactating dairy cows representing current levels of production.
1b. Approach (from AD-416)
1) The effects of PPO-modified plants, silage inoculants and lauric acid on protein utilization will be studied. Digestibility of corn silage with altered lignin/phenolic characteristics and alfalfa with down-regulated COMT and CCOMT to modify lignin will be evaluated with lambs and lactating cows. 2) Intake and digestibility from lactating cow trials will be compiled and digestibility of dry matter, fiber and soluble organic matter will be regressed on intake. Digestion kinetics will be measured on ration ingredients from trials. 3) In vitro fermentations using mixed ruminal microbes will be used to measure changes in digestion kinetics and microbial populations associated with direct-fed microbials, monensin, non-fiber carbohydrate sources, forage species and pH. 4) In vitro, lamb and lactating cow digestibilities will be compared to develop an integrated system for evaluating new forage genotypes.
3. Progress Report
An experiment identified the level of supplemental crude protein (CP), as soybean meal (SBM) and the amino acid methionine, in corn silage-based diets to optimize production of milk and milk components. Level of dietary CP affected production of milk, fat-corrected milk and milk fat, protein and solids-not fat. Yields of milk and true protein were lower on 12 and 14% compared to 16 and 18% dietary CP. Results indicated that 16% CP is required to optimize production of dairy cows fed corn silage-based diets supplemented with SBM plus methionine. Manure slurry from cows fed different legume silages varying in protein-binding polyphenols was land-applied to examine links between diet, excreta chemistry and the availability of excreta N to subsequent corn silage crops. Excreta were collected from a reduced-lignin corn silage lactation trial and an effective fiber-starch digestion trial. Chemical composition of these excreta is being analyzed, and if differences due to diet are found, excreta will be used in soil-incubation and greenhouse trials. An animal trial has been completed using fermented corn stover and chopped wheat straw as physically effective fiber sources. Histopathological evaluation of 79 cow tissues and blood samples has been completed, and discussions with pathologists are in progress to interpret results. There was no effect of a direct-fed microbial on digestion kinetics, but there was a transient increase in fiber digestion at 6 hours of fermentation. Inclusion of a direct-fed microbial altered the proportion of 7 of the 11 microbial species measured. Collection and analysis of intake, grazing behavior, and in situ digestion data from heifers grazing diverse temperate grasses was completed for the second year. Analysis of forage samples collected from pastures and rumen fluid collected from fistulated cows have been completed. Ruminal pH was recorded in 8 cows for 3 days. Ruminal samples were collected prior to and at 3 and 6 h post-feeding to determine bacterial community composition. Mean ruminal pH (5.89 to 6.50), and diurnal pH range (0.45 to 1.26) varied among cows. Bacterial community composition was similar in 6 of the 8 cows despite wide differences in pH dynamics. Two cows that displayed milk fat depression had pH profiles close to the mean of all 8 cows but unusual bacterial communities: high populations of the ruminal bacterium Megasphaera elsdenii and low populations of an unidentified bacterial species. Whole-plant corn silage was generated from bmr and sfe corn mutants, which have reduced ferulate and lignin, respectively. These silages were fed to lactating cows and young lambs to determine if altered ferulate in plant cell walls would result in similar improvements in production and digestibility as reduced lignin. Digestibility of fiber in several forages was measured (See project No. 3655-31000-021-03S for details). Samples of the forages fed in these digestion trials have been fermented in vitro for 12, 24, 48 and 96 h with inoculum collected from lactating cows. Chemical analyses have been completed for trials that compared digestibilities of total mixed rations when fed to lactating cows and young lambs.
1. Replacing rumen-degraded protein from soybean meal with that from urea reduced yields of milk and milk components. Microbial protein formed in the rumen provides most of the amino acids required by the dairy cow to form protein in milk and tissues. The nutritional model of the National Research Council, which is used throughout the world for formulating diets for dairy cows, assumes that rumen-degraded protein (RDP) from nonprotein nitrogen (NPN) compounds such as urea are as effective as RDP from true protein for supporting microbial protein formation in the rumen. U.S. Dairy Forage Research Center scientists used lactating Holstein cows to study the effects of feeding differing proportions of RDP from soybean meal and urea on cow production and rumen metabolism. Diets contained 40% corn silage, 15% alfalfa silage, 28-30% high moisture corn, plus varying levels of ground dry corn, solvent soybean meal, or urea plus a soybean meal that was treated to reduce its RDP content. All diets were formulated to contain 16.1% crude protein and 10.5% RDP, with urea providing 0, 11, 23 and 35% of the RDP in the 4 diets. Results indicated that replacing soybean meal RDP with urea RDP caused linear increases in the excretion of urinary urea nitrogen and in concentrations of milk urea-nitrogen, blood urea-nitrogen and rumen ammonia. Results also showed that replacing soybean meal RDP with RDP from urea reduced yield of milk and milk components, largely because of depressed microbial protein synthesis. The major impact of this research is that it shows that substituting RDP from urea for that from soybean meal (and probably other true proteins) will reduce milk production as well as farmer profits because of impaired microbial protein formation in the rumen. Saving money by replacing true protein with NPN is false economy. Dairy farmers are better off purchasing true proteins such as soybean meal to provide RDP for the rumens of their cows.
2. Specific changes in lignification of alfalfa improved fiber and dry matter digestibility by lambs, lactating dairy cows. Lignin limits the digestibility of plant fiber. Proof-of-concept studies of the lignin biosynthetic pathway by scientists in the Consortium for Alfalfa Improvement (Noble Foundation, Forage Genetics International, Plant Science Research Unit, U.S. Dairy Forage Research Center) have developed two lines of alfalfa with reduced lignin due to the down regulation of the cinnamoyl-O-methyl transferase (COMT) enzyme or the cinnamoyl-CoA-O-methyl transferase (CCOMT) enzyme in the lignin biosynthesis pathway. Multiple digestion trials were done with growing lambs with high intakes (>3.3% body weight/day) similar to those observed in lactating cows. Alfalfas from 1st, 2nd and 3rd harvests were fed alone to lambs and those from the first harvest were fed in total mixed rations (TMRs – 40% alfalfa hay, 10% corn silage, and 50% grain/protein supplement) to lambs and lactating dairy cows. Down regulating either enzyme reduced the lignin content. When fed alone at free-choice levels of intake, alfalfa with down-regulated COMT increased total and fiber digestibility, and alfalfa with CCOMT had a tendency to do so. When fed at restricted intakes, down-regulating both COMT and CCOMT improved the total and fiber digestibility. Improvement in digestibility was greater for down-regulating the COMT than the CCOMT. Results for reduced-lignin alfalfas, when fed in TMRs to lambs or lactating cows, were similar to those obtained when fed alone to lambs. However, the fiber digestibilities were reduced when fed in TMRs. These studies are proof of the concept that specific changes in the lignin biosynthesis pathway can alter lignin content and composition in ways that improve the digestibility of alfalfa. This knowledge will be extremely useful in developing specific strategies for genetically modifying alfalfa to improve its nutritional and economic value.
Contreras-Govea, F.E., Muck, R.E., Armstrong, K.L., Albrecht, K.A. 2009. Fermentability of Corn-Lablab Bean Mixtures from Different Planting Densities. Animal Feed Science And Technology. 149(3-4):298-306.