Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 30, 2007
Publication Date: December 5, 2007
Citation: Broderick, G.A. 2007. Estrategias para hacer el mejor uso de la proteina en raciones para vacas lecheras [CD-ROM]. In: Proceedings of Memorias de la Reunion Internacional de Leche y Forraje, December 5-7, 2007, Tapatitlan, Jalisco, Mexico. p. 20-32. Technical Abstract: Dairy cows utilize feed CP with greater efficiency than other ruminants, but still excrete about 2 to 3 times more 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 the most effective way to improve the protein status of the lactating cow. Only a portion of the dietary RDP can be replaced by NPN because RDP in the form of peptides and AA stimulates protein formation by the ruminal microbes. Ammonia is used best on diets that are high in NFC. Reducing grain particle size and heat processing of grains increases ruminal starch digestion and increases microbial protein formation, so long as ruminal pH is not depressed. Ration formulation models help predict how diet changes affect milk yield. Dietary CP not utilized for production is lost mainly in the urine, the most polluting form of excretory N. Reversal trials testing typical diets showed no increase in yield of 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 SBM did not give production equal to 16.6% CP. However, a second study showed that cows fed 15.8% CP plus 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.