Equine Performance Supplement For protein deficient diets, this equine performance supplement provides the three most essential amino acids needed by horses. Lysine aids in bone health and immune function. Methionine supplies essential sulfur, which can function as an antioxidant, can support the density of the mane & hair coat and plays a role in the synthesis of structural proteins, especially hooves and connective tissues. Threonine aids in normal immune function.