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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 . . .

AS EARLY as 1936, Arnold et al. demonstrated that casein was grossly deficient in arginine for young chicks. When casein was used as a source of protein, diets containing 0.57 or 0.86 percent arginine were greatly improved by arginine supplements, arginine carbonate or arginine HCl. Klose et al. (1938) showed that gains on a 20 percent casein diet were increased by the addition of 0.5 percent l -arginine HCl. Hegsted et al. (1941a) reported an increase in chick muscle creatine by adding 1 percent glycine and 0.5 percent arginine to a diet in which 18 percent casein and 10 percent yeast were used as sources of protein. A rapid feathering breed (White Leghorns) showed a greater growth response from the addition of arginine than a slower feathering breed (Plymouth Rocks). Hegsted et al. (1941b) reported that 5 percent gelatin added to an 18 percent casein diet usually supported good growth; however, . . .

WIETLAKE et al. (1954) reported a growth response, improved feathering, and elimination of an abnormal gait by adding arginine to a methionine supplemented 35 percent casein diet. Wietlake et al. (1954) and Savage et al. (1955) concluded that purified diets containing 25 percent casein, 10 percent gelatin, and methionine were partially inadequate as a source of protein for young chicks. Snyder et al. (1954) found a steady increase in growth up to an arginine level of 1.67 percent arginine in a 22 percent casein diet. Addition of arginine to a corn-soybean oil meal diet did not result in a significant growth response. Snyder et al. (1956) found a diet composed of 18 percent casein and 10 percent gelatin to be deficient in arginine. A total of 1.73 percent arginine was needed for maximal growth in a casein diet. A practical corn-soybean oil meal diet, calculated to contain 1.11 percent arginine . . .