One of the nine essential amino acids which must be provided by dietary sources. It is one of the sulphur containing ammino acids found at high levels along with cysteine in keratin in hoof horn, and methionine is often included in hoof supplements for this reason, though research to support the practice is yet to be done in horses. Research in cattle has not shown beneficial effect from methionine supplementation to hoof horn growth rate, quality, or resilience.
Methionine is present in forages including legumes like Lucerne and at higher levels in cereal grains and seeds, especially corn, flaxseed, and rice bran.