Use of Free Amino Acid Concentrations in Blood Plasma of Chicks to Detect Deficiencies and Excesses of Dietary Amino Acids

Abstract

A crystalline amino acid diet (reference diet) which contained each amino acid at the requirement level previously established by chick growth assay was used to study the effect of suboptimal and superoptimal dietary concentrations of amino acids on the free amino acid content of chick blood plasma. A comparison of plasma amino acid concentrations was made between chicks fed the reference diet and chicks fed the diet altered to create 1) amino acid deficiencies, 2) amino acid excesses and 3) combinations thereof. The feeding procedure used assured an equal intake of all nutrients except for the amino acid under study among experimental groups prior to the time that blood samples were taken. Also the frequency at which the chicks ate during the feeding period was controlled. Diets containing suboptimal amounts of either lysine or valine resulted in a marked lowering of the limiting amino acid and an increase in most of the other amino acids in plasma. A diet in which lysine and valine were demonstrated by growth assay to be first and second limiting, respectively, resulted in a decrease in these 2 amino acids in plasma, with lysine showing the greater decline. Most of the other amino acids in plasma increased as a result of this treatment. In some instances, plasma histidine appeared to be lowered as a result of the above mentioned deficiencies. A dietary excess of lysine resulted in a striking increase in plasma lysine and relatively small changes in other amino acids. However it did appear that arginine, glutamic acid and a mixture of glutamine and asparagine decreased as a result of the excess lysine. A diet containing suboptimal amounts of valine and threonine and superoptimal amounts of lysine, tyrosine and isoleucine resulted in marked changes in the corresponding amino acids in plasma; the former two decreased and the latter three increased. Relatively small changes were observed in other amino acids in plasma.