Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2005
Publication Date: March 29, 2006
Citation: Broderick, G.A. 2006. Strategies to reduce crude protein in dairy diets. Proceedings of 4th Mid-Atlantic Nutrition Conference, March, 2006, Timonium, Maryland. p. 1-14. Technical Abstract: Dairy cows utilize feed crude protein (CP) with greater efficiency than other ruminants but still excrete about 2-3 times more N in manure than they secrete in milk. This increases both cost of milk production plus environmental N pollution. Dietary CP supplies absorbed amino acids but extra CP not utilized for production is lost in the urine. Urinary N is the most polluting form of excretory N. Several trials testing various CP levels in diets formulated from typical feeds showed no increase in yield of milk, fat-corrected milk or protein with more than about 16.5% dietary CP. In one trial, feeding 15.6% CP with added rumen-undegraded protein (RUP) from soybean meal did not give production equal to 16.6% CP. Low solubles fish meal and canola meal were more effective sources of RUP than heated soybean products; cottonseed meal was less effective than soybean RUP. Feeding rumen-protected methionine also was effective for reducing dietary CP without losing milk yield. Monitoring milk urea can be used to assess both dietary CP and urinary N excretion in lactating cows. Ration formulation models are useful for predicting production responses to changes in dietary protein and carbohydrates. Hay-crop silages are the most degradable sources of dietary CP and replacing silage with hay will improve CP efficiency. Reducing grain particle size and heat processing increases ruminal starch digestion and increases microbial protein formation, so long as ruminal pH is not depressed. Future research developments will allow even lower dietary CP levels to be fed, thus reducing N excretion without losing production.