Influence of Dietary Zein on the Concentration of Amino Acids in the Plasma of Chicks

Abstract

The addition of 15% of zein to a diet containing 9.5% of soybean protein resulted in a significant reduction in weight gain and feed consumption, a marked decrease in the level of lysine in the deproteinized plasma, considerably smaller average decreases in the levels of arginine, glycine, histidine and tryptophan and increases in the levels of isoleucine, leucine, threonine and valine. It is suggested that the reduction in the level of plasma lysine may be related to the fact that a deficiency of lysine was limiting growth when the diet containing zein was fed. This conclusion is supported by the observation that the levels of tryptophan and arginine, which appeared to be the second and third amino acids limiting to growth, were reduced when the diet containing zein was supplemented with excess lysine. Also, a reduction in the level of tryptophan in the plasma was found when 15% of gelatin was added to the low-protein diet, rather than zein, thus producing a diet for which a deficiency of tryptophan was limiting growth.