Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 1, 2007
Publication Date: September 15, 2007
Citation: Powell, J.M. 2007. Cow diet and management impact nutrient losses from dairy farms. In: Chapman, D.F., Clark, D.A., Macmillan K.L. and Nation, D. P., editors. Meeting the Challenges for Pasture-Based Dairying. Proceedings of the Australian Dairy Science Symposium. 18-20 September, 2007. University of Melbourne, Victoria, Australia. p. 136-141. Technical Abstract: In the USA, regulations have been promulgated to minimize negative impacts of livestock farms on air and water quality. We conducted two integrated feed-manure management trials and a survey of dairy feed practices and to examine relationships between dairy diets, milk production, manure nutrient excretions and environmental risks. On Wisconsin dairy farms, approximately 20-35% of feed crude protein (CP) and phosphorus (P) is secreted into milk and the remaining is excreted in manure. The amount and form of N and P excreted in manure, and manure N and P losses to the environment are highly influenced by what is fed to dairy cows, and other management practices. For example, feeding dietary CP above recommended levels increases excretions of N in manure, especially of N in urine and also subsequent ammonia N loss in barns and after manure land application. Unnecessary dietary P supplements dramatically increase total and water-soluble P concentrations in manure, and also runoff P from soil surfaces after manure application. On Wisconsin dairy farms, the use of TMRs, balancing rations at least four times per year, and milking thrice daily results in highest milk yields and levels of feed N and P transformed into milk. In the USA, dietary options and practices are available that satisfy the nutritional requirements of high-producing dairy cows, and also produce manure less susceptible to environmental loss.