Rumen protected amino acids for dairy cows: past, present and future

Abstract Text: Considerable progress has been made in balancing dairy cow rations for amino acids (AA).  Research conducted over 40 years ago demonstrated that some AA (notably lysine and methionine) were more limiting than others.  The same research indicated that while selective protein supplementation would be important, rumen protected forms of these AA would also be needed as a first step to AA balancing.  Shortly after those findings, rumen protected Met (RP-Met) supplements became available and commercial usage started.   While sales of RP-Met supplements continued to increase in North America ever since, it wasn’t until more recently that RP-Lys supplements became available.  Their availability, in conjunction with improved guidelines for AA balancing and the higher value of milk protein, has been a boost for the sales of both supplements.  Coupled with continuing government pressure to reduce its environmental impact and the economic benefit of reduced protein feeding, the dairy industry is increasingly embracing AA balancing.  Implementation requires selective use of RP-AA, and there is every reason to believe their use will continue to increase and that other RP-AA (e.g., histidine) will also become available.  The benefits of AA balancing are well documented.  These include: 1) increased milk and milk component yields, 2) increased milk component percentages, 3) increased conversion of feed N to milk protein, 4) reduced need for supplemental rumen undegraded protein, and 5) increased herd profitability.  Of considerable interest are recent findings of AA balancing with transition cows.  The impact on early lactation performance has often been striking, and new research findings are starting to reveal why the responses are sometimes as profound as they are.  For example, some recent findings with RP-Met supplementation include: 1) a faster recovery to energy balance, 2) increased serum glucose levels, 3) reduced inflammatory signaling, 4) increased antioxidant capability, and 5) positive effects on embryonic development.  There is also evidence that increasing Lys and Met supplies could increase the capacity of the liver to export fat.  More research is needed to support these findings, but these results confirm the fact that most aspects of intermediary metabolism are impacted by protein synthesis and that alleviating an AA deficiency, particularly one like Met which has metabolic functions in addition to those of protein synthesis, is important to the health and performance of transition cows.  A better understanding of the AA requirements of transition cows would be helpful to obtaining a full appreciation of the impact of AA balancing.  

Keywords: amino acids, dairy cows