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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Dairy Forage Research

2012 Annual Report

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: 2/23/2016
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