What We Feed Dairy Cows Impacts Manure Chemistry and the Environment

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Why Be Concerned with Feed Rations and Their Environmental Implications?

During the last part of the 20th century, animal manure management became an environmental concern. In response to these concerns, legislation was enacted to control manure management and the emission of undesirable gasses (e.g., methane, ammonia, nitrous oxide) from animal production systems. The purpose of this paper is to illustrate how mineral phosphorus (P) supplements, forage types and amounts, and the crude protein (CP) fed to lactating cows impact manure chemistry and the fate of manure nutrients in the environment.

What Did We Do?

Source-sink relationships have been used to illustrate relationships between feed nutrient sources (e.g., forms and concentrations of P and CP in lactating cows rations) and nutrient sinks (milk and manure), and relationships between manure nutrient sources (e.g., soluble P, urea N) and sinks [soil test P, runoff P, atmospheric ammonia, soil inorganic nitrogen (N), crop N] and the impact of these relationships on the environment.

What Have We Learned?

As mineral P concentrations in dairy rations increase, the excretion of total P and soluble P in manure also increases. The amount of cropland needed to recycle manure P and runoff of soluble P from cropland after manure application can be related back to the P excreted in manure, which in turn can be linked to the amount of mineral P in cow rations.  Likewise, the type and amount of CP and forage fed to dairy cows impact manure chemistry and manure N losses as ammonia, N cycling in soil, including plant N uptake. Ammonia emissions from dairy barns and soil after manure application can be related back to the urea N excreted by dairy cows in urine, which is linked to the types and concentrations of CP and forages in cow rations, and the concentrations of urea in milk (milk urea N, or MUN).  Our results demonstrate that profitable rations can be fed to satisfy the nutritional demands of healthy, high producing dairy cows, reduce manure excretion and therefore the environmental impacts of milk production.

Future Plans

We continue investigations on how the feeding of tannins to lactating dairy cows, and the use of MUN as a management tool  may enhance feed CP use efficiency (more feed CP transformed into milk, less excreted in manure) and reduce losses of ammonia, nitrates and nitrous oxide from dairy farms.


J. Mark Powell, Soil Scientist. USDA-ARS U.S. Dairy Forage Research Center, Madison, Wisconsin,  mark.powell@ars.usda.gov

Glen A. Broderick,  Dairy Scientist,  USDA-ARS U.S. Dairy Forage Research Center, Madison, Wisconsin

Additional Information

Powell, J.M. and Broderick, G.A. Transdisciplinary soil science research: Impacts of dairy nutrition on manure chemistry and the environment. Soil. Sci. Soc. Am. J. 75:2071–2078.

Powell, J.M. Alteration of Dairy Cattle Diets for Beneficial On-Farm Recycling of Manure Nutrients. pp 21-42  In: Applied Research in Animal Manure Management. Zhongqi H. (Ed.) Nova Science Publ. Inc.

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


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