Amino acids in swine nutrition

Amino acids, normally supplied by dietary protein, are required for maintenance, muscle growth, development of fetuses and supporting tissues in gestating sows, and milk production in lactating sows. Of the 22 amino acids, 12 are synthesized by the animal; the other 10 must be provided in the diet for normal growth. The amino acids that make up proteins are conventionally classified as essential or non-essential. Essential or indispensable amino acids are not synthesized by the pig and must be supplied in the diet, whereas non-essential or dispensable amino acids are synthesized by the pig using nitrogen provided by proteins in the diet. Some amino acids are conditionally essential, amino acids with greater demand than synthesis under some conditions, i.e. depending on stage of growth, productive function, or dietary composition. The 10 essential amino acids for pigs are: lysine, methionine, tryptophan, threonine, valine, isoleucine, leucine, arginine, histidine and phenylalanine. Dietary supply of protein must be sufficient to provide all the essential amino acids and the nitrogen required for synthesis of non-essential amino acids. The amino acids of greatest practical importance in diet formulation (ie, those most likely to be at deficient levels) are lysine, tryptophan, threonine, and methionine. Corn, the basic grain in most swine diets, is markedly deficient in lysine and tryptophan. The other principal grains for pigs (grain sorghum, barley, and wheat) are low in lysine and threonine.