The Limiting Amino Acids in Soybean Protein

The sequence in which the amino acids of soybean protein become limiting was investigated in a series of experiments. Calculations based on knowledge of the animal's requirements and the amino acid composition of the protein found methionine most limiting followed by lysine, and threonine, and this sequence was used as the basis for establishing the various treatments. In 2 trials involving 66 pigs the belief that methionine was first-limiting was substantiated, but there was some indication that threonine was the second-limiting, rather than lysine. Two trials utilizing 128 rats clearly indicated that the sequence of limiting amino acids in soybean protein was methionine, threonine, and lysine in that order. An attempt to determine the fourth-limiting amino acid(s) was not successful.