Methionine: More Than Milk Protein

Methionine is one of the building blocks cows use to make protein, but its job does not stop there. It is also involved in cell function, energy production, how the body manages oxidative stress, how fats are processed and how other sulphur-containing compounds are produced. These roles help explain why methionine is being studied in relation to liver function, reproduction and hoof health, as well as milk production.

The amount of crude protein in the diet does not necessarily tell us how much methionine is available to the cow. Rumen microbes break down and rebuild dietary protein, which means in a ruminant the majority of methionine in feed is converted to ammonia before it can be absorbed. While ammonia is a useful feed source for bacteria, adequate levels of intact methionine within the intestine of a dairy cow is essential.

To boost intestinal levels of methionine, many farmers have turned to using specific forms of rumen-protected methionine. These are designed to pass through the rumen largely intact, allowing more methionine to reach the small intestine for absorption. However, that does not mean every herd will benefit from supplementation. What matters is the amount of absorbable methionine available compared with the cow’s requirements and the balance of the whole diet.

Supporting the liver through transition

The weeks around calving are demanding. Feed intake can fall behind rapidly rising energy requirements, body reserves are mobilised, and the liver has a heavy workload as the cow moves into milk production.

Methionine supports several processes that matter during this period. It supplies methyl groups used in everyday metabolic reactions, contributes to the way fats are packaged and transported, and helps produce glutathione, one of the body’s most important antioxidant compounds.

In a controlled study of cows around calving, Zhou and colleagues found changes in markers linked with liver function, inflammation and immune response when rumen-protected methionine was supplied. The cows also had higher concentrations of glutathione in their liver tissue.

This suggests methionine availability may influence some of the systems cows rely on during the transition period. As part of a nutritionally balanced diet protected methionine can help to prevent and even help to mitigate the effects of fatty liver disease in transition cows. However, carefully managing cow condition, feed intake, energy balance and good transition management still needs to be the focus.

A biological link with mating

Methionine is also involved in methylation, a process that helps regulate how cells grow and function. This gives it a biological link with oocyte quality, early embryo development and the maintenance of pregnancy.

Research results, however, have been mixed. In one study of 309 Holstein cows, Toledo and colleagues reported changes in embryo size and lower pregnancy loss among supplemented older cows, but not first-calving cows. The researchers said further work was needed to confirm the response.

A later and larger trial found no improvement in pregnancy rates or pregnancy loss.

The takeaway is not that rumen-protected methionine is a fertility treatment. Mating results are influenced by many factors, including energy balance, body condition, health, cycling and mating management. Amino acid supply is one part of that much larger picture.

Building blocks for hoof horn

There is also a straightforward connection between methionine and hoof growth. Hoof horn is largely made from keratin, and the sulphur-containing amino acids methionine and cysteine help form the bonds that give keratin its structure and strength.

Supplying the nutrients needed to grow sound hoof horn is important, but that is not the same as saying additional methionine will prevent or treat lameness. Lameness has many possible causes, including track and yard conditions leading to hoof injuries, hoof shape, cow flow, rumen acidosis, and nutrition.

Useful Questions

Useful questions we should ask are broader:

• What stage of lactation is the herd at, and what demands are being placed on the cows?
• What are the pasture and supplements providing in terms of metabolisable protein and amino acid balance?
• Is there evidence of a genuine nutritional gap, or are we simply assuiming more must be better?

Methionine is not another cure-all. Requirements and responses depend on dry-matter intake, the composition of the whole diet, metabolisable protein supply, amino acid balance and stage of lactation.

The important point is that an amino acid only has value if it reaches the small intestine and is available for the cow’s tissues to use.

Methionine may be best known for its connection with milk protein, but that is only part of the story. Its wider roles in liver metabolism, reproductive biology and hoof formation make it part of whole-cow nutrition, rather than simply another production input.

• Chris Balemi is Agvance Nutrition founder and managing director.