Partial alleviation of phenylalanine toxicity in the chick by supplemental dietary tryptophan. Poultry Sci

ABSTRACT Studies were conducted to determine the physiological effects of feeding diets containing high levels of phenylalanine to chicks. Marked reductions in weight gain and feed conversion were observed in birds fed a diet containing 2.52 % L-phenylalanine and.47 % L-tyro-sine. Excess dietary phenylalanine caused elevations of phenylalanine and tyrosine in serum and brain, whereas cerebral concentrations of free isoleucine, leucine, and valine were generally de-creased. Supraoptimal amounts of glycine, arginine, and tryptophan were fed in an attempt to alleviate the toxic symptoms observed in birds fed high phenylalanine diets. Only tryptophan supplementation proved successful in partially alleviating the growth-depressive effects of pheny-lalanine toxicity. Both serum and brain levels of tryptophan were increased by tryptophan sup-plementation. Results of two radiotracer studies with 14C-tryptophan suggested that brain uptake of tryptophan was inhibited by hyperphenylalaninemia