Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 19, 2010
Publication Date: May 12, 2010
Citation: Broderick, G.A. 2010. Supporting Production of Milk and Milk Components on Low Protein Diets. In: Proceedings of 46th Eastern Nutrition Conference, May 12-13, 2010, Guelph, Ontario, Canada. p. 199-211. Technical Abstract: There is increasing interest in minimizing crude protein (CP) content of diets fed to dairy cows to reduce production costs and to improve environmental sustainability. Dietary CP not utilized for production is lost largely in the urine, the most polluting form of excretory nitrogen (N). Because microbial protein formed in the rumen has an amino acid (AA) pattern very similar to milk, optimizing its formation is an effective means of improving protein status in lactating cows. However, N in microbial nucleic acids and bacterial cell walls is of little value to the animal. Nonprotein N can replace only a portion of the dietary rumen-degraded protein. Reducing grain particle size and heat processing increases ruminal starch digestion and microbial protein formation, so long as ruminal pH is not depressed. Although predictions made by ration formulation models may be inaccurate, models can be used to improve metabolizable protein supply and essential AA pattern of absorbed protein. This will help minimize dietary CP without sacrificing production. A number of reversal-type feeding trials found that there was no increase in yield of milk or components on typical diets with more than about 16.5% CP. One such trial showed that feeding 15.6% CP with added rumen-undegraded protein (RUP) from soybean meal (which is low in methionine [Met]) did not give production equal to 16.6% CP, but milk and component yield on 16.6% CP was equal to that on 17.6% CP. A second study showed that cows fed 15.8% CP plus rumen-protected Met yielded as much fat and protein as cows fed 17.1% CP without rumen-protected Met. Other reversal trials have suggested that overfeeding CP may even reduce milk and component yield. There are substantial differences in the effectiveness of RUP sources due to differences in AA profile. Rumen-protected lysine (Lys) should improve the value of the low Lys byproducts derived from ethanol production. Future research will explore ways to feed even lower dietary CP because of pressures to reduce N excretion.