Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 7, 2005
Publication Date: November 14, 2005
Citation: Broderick, G.A. 2005. Factors affecting microbial protein synthesis in the rumen with emphasis on diets based on tropical forages. In: Rowlinson, P.,Wachirapakorn, C., Pakdee, P., and Wanapat, M., editors. Integrating Livestock-Crop systems to meet the challenges of globalisation. 1:249-259. Technical Abstract: Inefficient utilization of the CP in ruminant diets, and the feeding of large amounts of protein supplements that this inefficiency necessitates, leads to excessive feed costs and environmental N losses in ruminant production. Maximizing microbial protein formation in the rumen is the most effective way to improve the protein status of the lactating ruminant. Only part of the dietary protein can be replaced by urea or other NPN sources because of a limitation in the ability of ruminal microbes to utilize the resulting ammonia as their sole source of RDP. Ammonia is used best on diets with greater amounts of NFC and/or higher digestible fiber; thus, enhancing the value of NPN supplementation on diets based on tropical forages is problematic. Feeding more extensively processed concentrate, if adequate effective fiber is maintained in the diet, will help maximize utilization of dietary NPN for microbial protein formation in the rumen. Replacing some dietary NFC with sugars or high-pectin feeds may be advantageous for improving ruminal microbial protein formation. As well as supplying ruminal energy, adding molasses to the diet stimulates intake and, thus, helps improve utilization of diets containing high-fibrous feeds and/or urea. The NRC (2001) model can also be used to match RDP with carbohydrate fermentation. Future research should be directed toward feeding only the required CP to minimize N excretion without losing animal productivity.