Amino acids serve as the ‚Äúbuilding blocks‚Äù of proteins. To make proteins for growth, development, and maintenance of tissues, the horse must have an adequate supply and balance of amino acids in the diet. The protein of many horse diets, especially those based on grains and grass hay and forage, is often low in lysine. The National Research Council calls lysine ‚Äúthe first limiting amino acid in the diet of growing foals....Inadequate protein or lysine intake results in decreased growth and development of young animals. Inadequate intake of protein or required amino acids by mature horses may lead to reduced feed intake, body tissue loss, poor hair coat, and reduced hoof growth.