Fifth-Limiting Amino Acids in Soybean Meal

A series of swine studies were conducted to determine the fifth-limiting amino acid in a simple corn-soybean diet for young pigs weighing about 20 kg. Performance of pigs fed a low-protein diet supplemented with amino acids was compared to pigs fed a 16 percent crude protein diet. The 11 or 12 percent low-protein diets were supplemented with lysine, tryptophan, threonine and methionine to levels equal to levels found in the 16 percent crude protein diets, plus various combinations of isoleucine, valine or histidine. The average daily gain and feed efficiency was reduced in pigs fed the low-protein diets. Plasma amino acid concentrations reflected the dietary intakes of the various crystalline amino acids, but were not helpful in identifying the sequence of limiting amino acids. Based on pig performance, the results of these experiments suggest that the fifth limiting is valine and the sixth limiting is either histidine or isoleucine in low-crude protein diets.

Figueroa, J.L. and co-workers. Growth, carcass traits and plasma amino acid concentrations of gilts fed low-protein diets supplemented with amino acids including histidine, isoleucine and valine. J. Animal Sci. 81(6): 1529-1537.