Casein as a Source of Protein for the Chick

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Abstract
When a synthetic diet which contained 25% of casein and 10% of gelatin was supplemented with 1.5% of glycine, there was an acceleration in the rate of gain, of uncertain significance. When supplemented with 1% of arginine, or with 1.5% of creatine, the chicks gained at the maximum rate for this laboratory. Casein alone as a source of protein for the chick is grossly deficient in arginine. The deficiency is completely, or almost completely, remedied by adding 1.2% of arginine to the diet. The optimum amount of total arginine in this diet is over 1.8% and probably less than 2.5%. When 1.5% of glycine was added along with 1.25% of arginine, the chicks gained at our maximum rate, but the increase in rate of gain due to glycine was small. The data give some support to Almquist's estimate that the diet of chicks should contain at least 1% of glycine. When suitable amino acid supplements were added to casein, to the casein-gelatin mixture, or to soybean oil meal, the rates of gain were unusally rapid and approximately equal.