Nutrition: Maximize Milk Protein Yield

USDA’s milk price announcement for March has milk components at $4.60 per pound for protein and $2.01 per pound for butterfat.

With these prices, a cow producing 85 lb. of a 3.1% protein and 3.8% fat milk returns $18.63 per day in protein and fat yield. Increasing milk protein to 3.2% can add another $0.39 per cow per 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 fat and protein. 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 both lysine and methionine is not new, but the payback has never been higher for pro­viding ration ade­quacy of these amino acids.

Bonus Content

More on amino acid balancing; Extended column Amino Acids in the Balance Q&A with Jim Linn Extended comments are highlighted in blue

Peter Robinson with the University of California-Davis has done a review of several 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 diets with rumen-protected lysine tended to decrease feed intake but increased feed efficiency, as overall 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. The response to supplementing rumen-protected lysine and/or methionine was variable but generally lowest with feeding of diets that were high in neutral detergent fiber (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 the effi­ciency that 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 to 1 ratio of lysine to methionine in diets.

Both Maryland researchers and Schwab pointed out that 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. The models’ weaknesses 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, it should not limit us from balancing dairy rations for amino acids. Fine-tuning the diets will be necessary. The starting guideline for optimal lysine and methionine levels in metabolizable protein are 7.2% and 3.2%, respectively, for a ratio of 3 to 1.

In general, keeping a ratio of 3 to 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, cows will excrete less nitrogen into the environment without loss of milk production.

JIM LINN is a dairy nutrition consultant and retired Extension nutrition specialist at the University of Minnesota–St. Paul. Contact him at linnx002@umn.edu.