Effect of Starvation and a Nonprotein Diet on Blood Plasma Amino Acids, and Observations on the Detection of Amino Acids Limiting Growth of Chicks Fed Purified Diets

Abstract

Chicks were fed a diet containing 15% of isolated soybean protein and then deprived of feed for periods of 12 to 48 hours. The removal of feed resulted in a marked elevation in the concentrations of lysine and threonine in the blood plasma, with maximal levels being recorded in 24 to 36 hours. Concentrations of glutamine, isoleucine, leucine and valine were also elevated, but to a considerably lesser degree, and concentrations of arginine, histidine, phenylalanine, tryptophan and tyrosine were depressed. When chicks received the nonprotein portion of the diet for 24 hours, rather than being completely deprived of feed, the concentrations of all amino acids investigated, including lysine and threonine were below values obtained when the complete diet was fed. Six diets with known or suspected amino acid deficiencies were fed, and plasma amino acid ratios were calculated for each amino acid by relating the plasma amino acid concentration, corrected for the concentration obtained when a nonprotein diet was fed, to the amino acid requirement. It was found that the ratios, on the basis of their relative magnitude, revealed the first and possibly the second limiting amino acids for the diets used.