Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 5, 2010
Publication Date: April 15, 2010
Citation: Broderick, G.A. 2010. Nuevas Perspectivas en la Efficiencia del Uso Nirogeno en Vaca Lecheras. In: Simposio: Alimentacion de la Vaca Lechara, April 15-16, 2010, Colonia, Uruguay. p. 5-18. Technical Abstract: Dairy cows utilize feed crude protein (CP) with greater efficiency than other ruminants, but still excrete about 2 to 3 times more nitrogen (N) in manure than they secrete in milk. This increases milk production costs plus environmental N pollution. Optimizing microbial protein formation in the rumen is an effective way to improve the protein status of the lactating cow. Nonprotein nitrogen (NPN) can replace only part of the dietary rumen-degraded protein (RDP) because RDP in the form of peptides and amino acids (AA) stimulates protein formation by the ruminal microbes. Ammonia is used best on diets that are high in starch and other nonfiber carbohydrates. Reducing particle size and heat processing increases ruminal digestion of grain starch and microbial protein formation, so long as ruminal pH is not depressed. Dietary CP that is not utilized for production is lost mainly in the urine, the most polluting form of excretory N. Ration formulation models help predict when lactating cows will respond to supplementation of rumen-undegraded protein (RUP). Reversal trials testing typical diets showed no increase in yield of milk, fat-corrected milk (FCM), or protein with more than about 16.5% dietary CP. One such trial found that feeding 15.6% CP with added RUP from soybean meal did not give production equal to 16.6% CP. However, a second study showed that cows fed 15.8% CP plus rumen-protected methionine (RPM) yielded as much milk, fat, and protein as cows fed 17.1% CP without RPM. There are substantial differences in the effectiveness of different sources of RUP for lactating cows due to differences in AA profile. In future research, it may be necessary to find ways to feed even lower dietary CP levels because of regulatory pressures to reduce N excretion.