Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2003
Publication Date: 10/30/2003
Citation: Broderick, G.A. 2003. Protein precision feeding in the dairy cow. Proceedings of the ARPAS, California Chapter, Continuing Education Conference. p. 17. Interpretive Summary:
Technical Abstract: Dairy cows make inefficient use of high protein diets, necessitating supplementation with large amounts of protein. This increases feed costs for milk production and contributes to environmental N pollution. The large amounts of N lost from the concentrated dairy operations in California contaminate surface and ground waters and are volatilized as ammonia. In the future, dairy farmers likely will be held more accountable for the environmental impacts from animal excreta. Dairy farmers and the consultants that advise them often over-feed protein because of great variation, and constantly changing origins, of feedstuffs. This makes it necessary to frequently collect and analyze representative samples of dietary ingredients. Monitoring milk urea N can serve as useful technique to identify diets that were relatively low or high in crude protein content. Using nutritional models to formulate dairy cow rations is useful to more closely match diets to protein requirements but these models must be applied with adjunct information and guidelines. When forages are ensiled, plant cell rupture releases proteases that break down forage proteins to NPN; NPN typically accounts for more than 50% of the crude protein in alfalfa silage. Degradation of hay protein appears to be more synchronous with ruminal microbial growth and results in more efficient capture of degraded N than with silage protein. High milk yields in the West result at least partly from much greater feeding of alfalfa as hay rather than silage. Because microbial protein accounts for most of the dairy cow's metabolizable protein, diets must first meet all of the requirement for degraded protein. Matching ruminal energy fermentation with degraded protein will be effective for improving N efficiency. Feeding large amounts of processed concentrate will stimulate maximal microbial protein formation and help meet the lactating cow's demand for energy. However, sufficient fiber must be fed to maintain long-term rumen and animal health. Post-ruminal supplementation with specific limiting amino acids will help meet requirements with relatively little extra N input. A possible future stratagem might be to feed ruminally protected keto acids of amino acids to provide these limiting nutrients without N to reduce N excretion to the environment from lactating cows.