Effects of D-, DL-and L-glutamic acid on chicks

Studies were conducted to investigate the effects of D-, DL-, or L-glutamic acid on the chick. Supplementation of levels of L-glutamic acid to an amino acid mixture containing adequate levels of all the indispensable amino acids plus cystine and tyrosine resulted in increased growth up to 10% L-glutamic acid in the diet. Chicks tolerated as much as 15% L-glutamic acid with no growth retardation. Supplementation of D-glutamic acid at levels of 3.75 or 5% resulted in growth depressions of 18 and 38%, respectively, at the end of a 2-week experiment. Significant growth-depressing effects of these levels of D-glutamic acid and 7.5% of DL-glutamic acid were also observed with an amino acid diet as well as an isolated soybean protein diet. The growth-depressing effect was most severe during week 2 of the experiment. Additional vitamins and amino acid supplements failed to reverse the growth-depressing effect. Plasma glutamic acid concentration was not altered by the inclusion of D-glutamic acid in the diet, but generally, plasma free amino acid concentrations were increased. This was especially true of arginine. Free glutamic acid increased in the kidney and was lowered in the liver. Free ammonia was increased in both the liver and kidney when the D form was included in the diet. Implications of these findings are discussed.