Phenylalanine and Threonine Levels for Young Chicks

GRAU (1947) indicated that chicks require 0.6 to 0.8 percent dl -phenylalanine in the diet plus an equal amount of tyrosine. Almquist (1952) and the National Research Council (1954) gave the requirement for phenylalanine as 1.6 percent of the diet, 0.7 percent of which may be replaced by tyrosine. Fisher (1956) found the phenylalanine requirement to be about 0.5 percent of the diet in the presence of excess tyrosine. Almquist and Grau (1944) indicated that 1.0 percent dl -threonine appeared to be insufficient to support growth in a diet composed of pure amino acids. Wilkening et al. (1947) stated that 0.67 percent l -threonine from oxidized casein and gelatin apparently satisfied the chicks’ requirement for threonine. Grau (1949) concluded that the l -threonine requiredent is approximately 0.45 percent of the diet. dl -threonine was only one-half as active as l -threonine. Lewis (1951) reported that a diet containing 27 percent crude protein from wheat gluten and . . .