By: Jim Linn
USDA’s milk price announcement for March has milk components at $4.60/lb. for protein and $2.01/lb. for butterfat.
With these prices, a cow producing 85 lb. of a 3.1% protein and 3.8% fat milk returns $18.63/day in protein and fat yield. Increasing milk protein to 3.2% can add another $0.39/cow/day for a return of $19.02 at the same milk and fat production.
As a result, a 500-cow herd could increase milk revenue by $6,000 per month by increasing protein 0.1%.
Nutrition affects both of these components. One way to help to maximize production of both is to balance lactation diets for lysine and methionine. Optimizing the amount and ratio of these two amino acids can help achieve maximum production of both milk protein and fat garnering a high a return on milk production.
Balancing diets for lysine and methionine is not new, but there has not been a time when ration adequacy of these amino acids has had such a high payback. Peter Robinson, with the University of California-Davis, has done a review of feeding studies measuring production performance along with duodenal flow of lysine and methionine in lactating dairy cows.
He concludes that the response to feeding rumen protected methionine increased milk energy output, milk protein and milk fat percentages. Supplementing rumen protected lysine in diets tended to decrease feed intake, but increased feed efficiency as milk production was unaffected.
Supplementing rumen protected methionine and lysine together resulted in production responses similar to those of methionine alone. All of the responses to methionine, lysine or methionine plus lysine supplementation were affected by diet composition and not always predictable.
In general, the response in milk fat percent to methionine supplementation tended to decrease as corn products in the diet increased, but with adequate lysine from protein supplements milk protein percent increased. Response to supplementing rumen protected lysine and/or methionine was variable but generally lowest with feeding of diets high in NDF, legume/grass forages, or crude protein.
University of Maryland researchers Diwakar Vyas and Rich Erdman summarized 23 studies where rumen protected methionine and/or lysine was fed or infused post-ruminally. They found supplementing metabolizable methionine and lysine in rations increases milk protein, methionine greater than lysine, but efficiency at which these two amino acids increase milk protein decreases as supplemented amounts increase.
A more recent review on the subject of amino acid nutrition of lactating cows by Chuck Schwab with the University of New Hampshire also indicates methionine is more likely to be limiting in diets than lysine. He also found that metabolizable lysine is generally in excess of the required 3:1 ratio of lysine to methionine in diets.
Both Maryland researchers and Schwab pointed out the models used in formulating rations have limitations in their ability to accurately predict responses in milk protein and milk production from metabolizable protein and amino acids in the diet. Weakness of the models are likely centered on prediction of microbial protein production, which is a good source of lysine, and the nonlinear decreasing efficiency use of these amino acids for production as supplies increase.
Even though our knowledge of the protein and amino acid biology of the cow isn’t perfect, that should not limit us from balancing dairy rations for amino acids. Fine-tuning of diets will be necessary. The starting guideline for optimal lysine and methionine levels in metabolizable protein are at 7.2% and 3.2%, respectively, for a ratio of 3:1.
Knowing that guidelines are not absolute, keeping a ratio of 3:1 at a target lysine of 6.5 to 6.7% is more achievable while maintaining an adequate rumen degradable protein (target – 65% of crude protein) in the diet.
The other benefit is that a correct amino acid balance will lower the crude protein content of the diet. As a result of that, cows will excrete less nitrogen into the environment without loss of milk production.