In horses, lysine is the first limiting amino acid meaning it is most likely to be low in the diet relative to physiological requirements. Protein synthesis rates will not be optimal until there is enough lysine available. Methionine and threonine are often considered the second and third limiting amino acids for horses.
Horses that have poor hoof growth, poor coat quality, or loss of muscle mass might have a protein deficiency in their diet. Low milk production in lactating mares and poor stamina are additional signs of deficiency.
Ensuring that your horse receives adequate levels of lysine, methionine, and threonine in their diet could correct amino acid imbalances, supporting normal function of all tissues in the body.