Research - Animal Nutrition Management

The goal of our research is to reduce pollution of air and water resources from animal agriculture. Nutrient pollution is a major concern in the Chesapeake Bay Watershed because high levels of nitrogen and phosphorus threaten the Bay's ecosystem. Our emphasis has been to identify ways to reduce nutrient pollution from animal agriculture through better animal nutrition and farm management. Most of our research employs the use of mathematical models to integrate information in the scientific literature, develop and test scientific hypotheses, integrate data from experiments we conduct, and ultimately develop tools that can be used in the field.

We developed a mathematical model of a dairy farm that was used to identify the critical control points for reducing nutrient losses to the environment. This model integrated effects of animal nutrition and feeding with crop selection and manure management decisions, and demonstrated the important impact of animal feeding on reducing nitrogen and phosphorus losses to the environment. We have compared the effects of different technologies using data from controlled experiments and from field observations.

One of the most important nutrients to farming is nitrogen. Improving protein utilization by cattle allows for maintenance of production levels with reduced nitrogen feeding and excretion. This effect in turn leads to a decreased requirement to purchase and grow protein sources on the farm (protein is an expensive nutrient to obtain). Ultimately, protein nutrition has a major impact on both farm profitability and nitrogen losses to water and air resources. Several of our research projects have suggested ways to improve nitrogen utilization in dairy cattle. We have also developed mathematical models of nitrogen metabolism by dairy cattle to better understand requirements and to identify indicators of excessive or deficient diets. We developed a means to evaluate the amount of protein consumed on farms using milk composition. High levels of urea nitrogen in milk samples indicate that cows consumed more than enough protein for their level of production. Further research is aimed at evaluating methods to assess protein degradation and microbial protein synthesis in the rumen from milk or urine composition.

Future research will aim to develop methods to quantify microbial growth in the rumen in order to assess the requirement for protein and energy in the diet that is available to rumen microbes. We are also exploring ways of grouping cows and determining the optimal diet to feed a group, and we are developing protocols for making feed selection choices while taking environmental and economic considerations into account.

Awards and Honors

• Junior Faculty Award for Excellence, College of Agriculture and Natural Resources, May, 2001
• Agway Young Scientist Award for Dairy Nutrition Research, American Dairy Science Association, 2002
• Award for Excellence in Research from the Univ. of MD Alumni Association, Agr. and Nat Resources Chapt, 2004

Publications

• Jonker, J. S., R. A. Kohn, and J. High. 2002. Dairy herd management practices that impact nitrogen utilization efficiency. J. Dairy Sci.
• Dunlap, T. F., R. A. Kohn, G. E. Dahl, R. A. Erdman, and M. Varner. 2000. The impact of bovine somatotropin, three times daily milking or extended photoperiod on nitrogen flows from dairy farms. J. Dairy Sci. 83: 968
• Kalscheur, K .F., J. H. Vandersall, R. A. Erdman, R. A. Kohn, and E. Russek-Cohen. 1999. Effects of dietary crude protein concentration and degradability on milk production responses of lactating dairy cows. J. Dairy Sci. 82: 545-554.-976.
• Jonker, J.S., R. A. Kohn, and R. A. Erdman. 1998. Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cattle. J. Dairy Sci. 81: 2681-2692.
• Kohn, R. A., Z. Dou, J. D. Ferguson, and R.C. Boston. 1997. A sensitivity analysis of nitrogen losses from dairy farms. J. Environmental Management 50: 417-428.

Grants