I’ve written about soil sulfur and methionine deficiency often. Everything I’m seeing says it’s getting worse.
Methionine is an essential amino acid, meaning horses must get it from their diet. It is critical in protein synthesis since many proteins start with methionine and without it synthesis will stop.
Methionine is the king of the sulfur-containing amino acids which give strength to hair, hoof horn, skin and tendons/ligaments. It is the precursor for SAM-e, a mood stabilizer, and the major antioxidant glutathione.
Methionine is a methyl donor required for the synthesis of L-creatine and L-carnosine. These compounds are critical to muscle function and athletic performance.
Soybean, peas and beet pulp are poor methionine sources. Historically, grains, brans and other seed meals were adequate sources. Hays easily met the 0.2% sulfur content most authorities recommend to support production of good levels of sulfur-containing amino acids. This is changing.
I am increasingly seeing hay analyses with sulfur below 0.2%, even below 0.1%. This means soil levels are low so grains will also be affected. What’s going on?
A positive result of the industrial revolution and burning of fossil fuels was the release of sulfur into the atmosphere. Sulfur is essential for plants and became so abundant that farmers no longer needed to add it to fertilizers. However, with the appearance of pollution controls in the late 1980s and 1990s, sulfur emissions were curtailed. Cleaner, but soil sulfur has suffered.
It wouldn’t surprise me if methionine comes to rival lysine as the most commonly deficient amino acid. If you analyze your hay, make sure it includes sulfur. Otherwise, methionine should be supplemented as routinely as lysine at about half the lysine level, such as in Three Amigos .
Very severe methionine deficiencies can cause poor muscling and stark coats which do not respond to mineral balancing. Brittle hooves with superficial or deep cracks are also common. In these cases, methionine supplementation at 10 grams/day or more is needed.
Eleanor Kellon, VMD
Dr. K's Horse Sense 
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Commercially produced (soy-based) animal feed already includes supplemental methionine, since this is a well-understood issue in raising chickens on a soy diet. If you’re looking to grow your own supplements, hemp seed contains both methionine and lysine, as well as the semiessential arginine.
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It’s widely known that soy is a poor methionine source regardless of available soil sulfur. It’s the genetics of the plant. Hemp is a good methionine/cystine source but not lysine. Lysine percent of crude protein is low.
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Thank you for all the work you do and sharing this information. Since getting our horses on a forage based diet with balanced minerals and added aminos such as Tri Amino, we have seen a remarkable difference in the health of our horses, and dramatic improvement in hoof health and their coats are shining even in full winter coat!! So grateful for scientific knowledge shared in layman’s terms.
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Once again, thank you for getting resourced, reliable knowledge and application to our horses and their health.
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