Insights on how to achieve optimal herd performance by balancing the amino acid levels in rations were provided by Chuck Schwab, Professor Emeritus, University of New Hampshire, and owner of Schwab Consulting, at the recent 2018 Adisseo International Dairy Workshop. The workshop provided insights and solutions for dairy producers such as the benefit of supplemental methionine, a required nutrient.
Dr. Schwab focused on five key points:
He reminded dairy farmers that while rumen microorganisms require rumen degradable protein, cows require amino acids. Therefore, the best dairy rations meet the needs of both the rumen microorganisms and the cows. Cows use amino acids in three ways: For protein synthesis, metabolic regulation, and the formation of non-protein nitrogen compounds.
Dairy cows obtain absorbable amino acids from microbial protein (usually 50% or more), the rumen undegraded protein in their feed (usually less than 45%), and endogenous protein (approximately 5%). Of the 20 amino acids dairy cows use, 10 are essential. This means that sufficient amounts must be provided by microbial protein and feedstuffs. They cannot be created by the cow herself. Notable among these 10 essential amino acids (EAA) are methionine and lysine. These are the first limiting EAA. They typically are the first EAA whose requirements are not adequately supplied by rations. They will be the first amino acids to limit the cow’s production and performance.
Schwab recommends using rumen protected amino acids to ensure that neither a lack of methionine or lysine limits production or performance. He encourages nutritionists to selectively use protein supplements and rumen protected amino acids to more efficiently and economically meet their nutrient requirements without wasting amino acids.
Before using a rumen protected amino acid, he stresses the need to confirm its bioavailability: how much of the amino acid fed is absorbed by the animal. This can be done through a review of the research literature. He suggests paying particular attention to the results of work done using the plasma free amino acid dose-response method as conducted by researchers at the University of New Hampshire. This work has become recognized for its accuracy in determining bioavailability.
Schwab says more research is needed to establish the ideal profile of absorbed amino acids at different stage of lactation and production levels.
He also foresees that protein and amino acid nutrition will continue to evolve to more efficiently meet the requirements of the cow while allowing for lower levels of dietary crude protein. For example, current research shows that the functions of methionine go beyond being a building block for protein synthesis. Methionine plays a role in production, health, and reproduction. And it does this by not only increasing protein synthesis but also by affecting antioxidant levels, liver function, the immune system, methylation of DNA and histone, and gene expression.
Guidelines for amino acid balancing from Dr. Chuck Schwab
- Feed a blend of high-quality fermentable feeds and physically effective fiber to optimize rumen function, maximize feed intake, and maximize the yield of microbial protein.
- Feed adequate amounts of rumen degradable protein to optimize rumen function, maximize feed intake, and achieve targeted levels of milk urea nitrogen. Milk urea nitrogen levels serve as a tool to assess the adequacy and balance of rumen degradable protein and rumen fermentable energy.
- Feed high-lysine protein supplements, possibly in combination with a proven rumen-protected lysine, to achieve a lysine level in metabolizable protein that approaches the optimal concentration.
- Feed a rumen-protected methionine to achieve the optimum lysine:methionine ratio in metabolizable protein. Fine tune the level fed, based on herd performance, to produce maximal milk protein concentrations.
- Limit rumen undegraded protein supplementation to only what is needed. After peak lactation, reductions of 1-2 percentage units of dry matter are common with AA balancing.