Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 15, 2007
Publication Date: N/A
Technical Abstract: Dairy cows utilize feed crude protein (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 protein can be replaced by NPN because of the limited ability of ruminal microbes to utilize ammonia as their sole RDP source. Ammonia is used best on diets that are high in NFC and highly digestible fiber; thus, supplementing with NPN on diets based on low-quality forages is problematic. 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. Feeding sugars and other soluble carbohydrates may improve microbial protein formation in the rumen. Ration formulation models help predict how diet changes affect milk yield. Dietary CP not utilized for production is lost 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 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 rumen-protected methionine yielded as much as cows fed 17.1% CP without rumen-protected methionine. There are substantial differences in the effectiveness of different sources of RUP for lactating cows. Future research findings may allow feeding of even lower dietary CP levels so as to reduce N excretion without losing production.