|Pauly, Thomas -|
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 29, 2013
Publication Date: July 22, 2013
Citation: Broderick, G.A., Muck, R.E., Pauly, T. 2013. Relationship between proteolysis in the silo and efficiency of utilization of dietary protein by lactating dairy cows. Proceedings of the III International Symposium on Forage Quality and Conservation, FEALQ, Piracicaba, SP, Brazil. pp. 47-68. Technical Abstract: Ensiling is used widely to conserve forages for feeding to dairy cows. However, the protein in hay-crop silages is particularly susceptible to microbial breakdown in the rumen, and utilization of protein in alfalfa and grass silages by dairy cows is particularly poor. Dependent on maturity, hay-crop forages contain substantial amounts of crude protein, and the essential amino acid pattern of these proteins is often of good quality. Unfortunately, more than half of the crude protein in alfalfa is converted to nonprotein nitrogen during the ensiling process. Comparing alfalfa silage to alfalfa hay as the primary forage source for lactating dairy cattle, both milk and milk protein yields will be adversely affected unless the silage-based rations are supplemented with rumen undegraded protein or a fermentable energy source. Various methods have been studied to reduce proteolysis during ensiling, including acid and inoculant additives applied at ensiling. Both types have been shown to improve nitrogen (N) utilization in dairy cows. Research on other legumes has identified natural mechanisms within plants for reducing proteolysis during the ensiling process. Birdsfoot trefoil and red clover have two different means for improving N utilization by dairy cows compared to alfalfa. Birdsfoot trefoil has tannins that have modest effects on proteolysis in the silo but increase rumen undegradable protein and N utilization. Red clover has polyphenol oxidase (PPO) enzymes that reduce proteolysis in the silo, leading to increased N utilization in the cow. Both legumes are agronomically inferior to alfalfa, and efforts are ongoing to add tannins or the PPO system to alfalfa. Consequently, farmers today must use additives at ensiling or appropriately supplement rations based on hay-crop silages like alfalfa to maximize N utilization. In the future, we are hopeful that alfalfa and similar forage species may be genetically modified to improve silage N utilization by cattle without supplementation.