Location: Dairy Forage Research2011 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
Feeding cows alfalfa silage inoculated with a commercial silage inoculant known to improve in vitro ruminal microbial protein synthesis resulted in only minor differences in the in vivo ruminal bacterial community composition compared to cows fed silage from the same alfalfa not prepared with the inoculant. However, cows that produced milk with low fat content also had the most unusual ruminal bacterial community compositions and had relatively abundant populations of the bacterium Megasphaera elsdenii. All sample and data analysis were completed for the dairy cow lactation trial for the reduced ferulate cross linking sfe corn mutant. Feces and urine were collected separately from a lactation trial with cows fed four levels of tannin extract from red quebracho and chestnut trees, each at two levels of dietary crude protein (CP). The excreta was used in three lab-scale trials to assess dietary tannin and CP impacts on ammonia emissions from dairy barn floors: (1) mixtures of feces and urine were applied in the mass ratio they were excreted; 2) urea solution was added to feces excreted by cows fed tannins at the high CP level; and 3) tannin was applied directly to feces-urine mixtures (rather than feeding it). Tannin feeding or direct application reduced ammonia emissions from barn floors in all three experiments. For the low CP diet, average ammonia emission reductions of 30% could be attributed to feeding tannin. For the high CP diet, ammonia emissions reductions of 16% were due to tannin. Feeding tannin also decreased urease activity in feces resulting in an ammonia emission reduction of 12%. The application of tannin directly to the barn floors resulted in an ammonia emission reduction of 19%. A lactation trial tested the value of supplementing dairy cows being fed either alfalfa silage or red clover silage as their principal forage, with rumen-protected methionine, rumen-protected lysine, or both. This was done to assess whether the enzyme polyphenol oxidase in red clover causes specific loss of either of these essential amino acids. Results from this experiment showed similar production responses to the rumen-protected methionine in cows fed alfalfa or red clover silage. No response to rumen-protected lysine was detected on either forage. These results indicate that polyphenol oxidase does not result in sufficient loss of available lysine in red clover to make that amino acid more limiting than methionine. Moreover, the similar response to rumen-protected methionine on both forages suggests that red clover protein is limiting in sulfur-amino acids in much the same way as other legume proteins. Plasma amino acid analyses are being used to confirm the effectiveness of the rumen-protected amino acid supplements.
1. Understanding how silage additives improve milk production. Bacterial inoculants (lactic acid bacteria) are added to forage crops at ensiling by more than half of all farmers in the U.S. to ensure a good fermentation in the silo, minimize storage losses and increase milk production. It has long been understood how these products improve preservation in the silo. However, the biggest return on investment from using these additives comes from increased milk production, an effect that is neither consistent nor understood. In screening a number of commercial inoculants, ARS researchers at Madison, Wisconsin found that silages treated with certain inoculants produced more rumen microorganisms than untreated silages in laboratory digestion trials. Microorganisms in the rumen of the cow are a major source of protein for the cow, and increased microbial production potentially explains why cows produce more milk on inoculated silage. Beyond explaining how inoculants may affect the cow, these results may be useful to the companies that produce inoculants, allowing them to more rapidly screen for bacteria that help the cow make more efficient use of her diet.
2. More digestible corn silage. Corn silage is a major feed resource for livestock, but fiber digestibility of the stover fraction is poor. A corn mutant with reduced ferulate cross linking, an inhibitor of fiber digestion, was fed to lactating dairy cows by ARS researchers at Madison, Wisconsin, as part of a typical mixed ingredient diet. Cows fed the mutant corn silage ate more feed, did less sorting of their feed to avoid fiber, digested more fiber, and produced more milk. Because corn is a type of grass, if the gene responsible for cross linking can be isolated from this corn mutant, then the digestibility of all grass forages, not just corn silage, can be improved genetically.
Weimer, P.J., Stevenson, D.M., Mantovani, H., Man, S. 2010. Host specificity of the ruminal bacterial community in the dairy cow followng near-total exchange of ruminal contents. Journal of Dairy Science. 93:5902-5912.