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United States Department of Agriculture

Agricultural Research Service

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Location: Dairy Forage Research

2012 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:
This report summarizes progress over the project life. Various experiments investigated mechanisms to increase nitrogen (N) efficiency in lactating dairy cows. Lauric acid was expected to increase efficiency by suppressing rumen protozoa but had negative effects on milk production because it depressed feed intake. In corn silage-based diets supplemented with soybean meal and rumen-protected methionine (RPM), production was optimized when the diet was adjusted to 16% crude protein. Feeding RPM maintained or increased milk production while reducing urinary N excretion. Lactating cow experiments also compared various sources of physically effective fiber including corn stover, wheat straw, grass, and alfalfa stems, and found differences between sources and interactions with the rate of starch digestion. Urine and feces were collected in many of these experiments to determine effects on manure composition, ammonia volatilization from manure, and mineralization of manure N when applied to soil. Feeding N above recommended levels increased N in manure and increased ammonia volatilization both in the barn and after field application. Tannins, whether fed or added to the barn floor, reduced ammonia emissions. Diets that reduced milk urea N, not only improved N efficiency in the cow, but also reduced urine N and ammonia emissions. Bacterial inoculants for making silage were investigated to determine how they affected milk production. In vitro experiments determined that some inoculants increased ruminal microbial growth. Alfalfa inoculated at ensiling with one of these inoculants increased milk production compared to untreated silage; lower levels of milk urea N levels on the inoculated silage indicated improved N efficiency. The rumen bacterial community was not appreciably affected by which silage was fed, but increased microbial flow from the rumen is expected when analyses of omasal samples are complete. In studies on rumen microbial community composition, the particle-associated bacterial community was found to be more stable and distinct from the liquid-associated community. Bacterial communities differed considerably between cows. Nearly complete (>95%) exchange of rumen contents between cows with differing communities temporarily changed the community in each cow, but within weeks the community returned to the original distribution. Milk fat-depressed cows had higher levels of Megasphaera elsdenii. Heifers maintained on orchardgrass pasture (OGP) over a 3-month period displayed stability in bacterial community composition. By contrast heifers switched from OGP to orchardgrass hay displayed shifts in community composition, and these shifts were reversed upon return to grazing. Digestibility measured in vitro, in young lambs and lactating cows was used to develop an integrated system for evaluating new forage genotypes, from small plots through seed increase to field quantities. Lambs proved to be a good model for evaluating forage digestibility, giving results comparable to those in lactating cows. Several forages were successfully evaluated with this system including reduced lignin alfalfa and a corn mutant with reduced ferulate cross-linking.

4. Accomplishments
1. Controlling ammonia emissions from dairy farms through diet. Cows excrete urea nitrogen in urine, which is converted rapidly and lost as ammonia gas into the atmosphere. Milk urea nitrogen (MUN) testing was developed to help dairy producers and nutritionists evaluate the protein levels and nitrogen use efficiency of dairy cattle diets. ARS scientists at Madison, Wisconsin, determined that MUN is also a reliable indicator of concentrations of urea in urine and ammonia emissions from dairy farms. The results of six feeding trials were analyzed to determine the relationships between feed nitrogen intake, MUN, and ammonia emissions from dairy barns. Ammonia emissions dropped between 10 and 34% when MUN levels decreased from 14 to 10 mg/dL. Feeding less nitrogen would be a win-win situation, saving dairy producers approximately $740 million annually in reduced feed nitrogen costs and improving environmental quality through reduced ammonia emissions.

2. Silage inoculant improves the nitrogen efficiency of dairy cows. Inoculants, i.e., lactic acid bacteria, are commonly added to forages to enhance preservation in silos, and some inoculants increase milk production 3 to 5%. However, it is unclear why lactic acid bacteria added at the silo increase milk production. ARS scientists at Madison, Wisconsin previously found that certain inoculated silages, compared to untreated silage, increased the growth of microorganisms in fluid from the main stomach of the cow. These microorganisms are the biggest source of protein for the cow. In the current study, lactating dairy cows that were fed inoculated silage produced 2 lbs. /day more milk, compared to the cows on untreated silage, and this milk contained 10% less urea nitrogen, a marker of how efficiently the cow is using the nitrogen in her diet. Less urea in milk means proportionately less nitrogen excreted in urine and ultimately less ammonia entering the atmosphere from the farm. Using the results of this study, the inoculant costs the farmer approximately $0.03/cow/day and returns to the farmer $0.30/cow/day in increased milk production while reducing ammonia emissions from the farm by 5% - an inexpensive additive that increases profitability while reducing the environmental footprint of the farm.

Review Publications
Mohammed, R., Stevenson, D.M., Beauchemin, K.A., Muck, R.E., Weimer, P.J. 2012. Changes in ruminal bacterial community composition following feeding of alfalfa silage inoculated with a commercial silage inoculant. Journal of Dairy Science. 95:328-339.

Powell, J.M., Wattiaux, M.A., Broderick, G.A. 2011. Evaluation of milk urea nitrogen as a management tool to reduce ammonia emissions from dairy farms. Journal of Dairy Science. 94:4690-4694.

Weimer, P.J., Stevenson, D.M., Mertens, D.R., Hall, M. 2011. Fiber digestion, VFA production, and microbial population changes during in vitro ruminal fermentations of mixed rations by monensin-adapted and unadapted microbes. Animal Feed Science And Technology. 169:68-78.

Powell, J.M., Broderick, G.A. 2011. Trans-disciplinary soil science research: impacts of dairy nutrition on manure chemistry and the environment. Soil Science Society of America Journal. 40:907-914. DOI:10.2134/jeq2010.0492.

Powell, J.M., Aguerre, M.J., Wattiaux, M.A. 2011. Dietary crude protein and tannin impact dairy manure chemistry and ammonia emissions from soils. Journal of Environmental Quality. 40:1767-1774. DOI:10.2134/jeq2011.0085.

Last Modified: 08/18/2017
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