Methionine and arginine supplementation of casein-based high fat diets: Effects on rat growth

The effects of methionine and arginine supplementation on protein adequacy of two commercial caseins (ANRC and U.S. Biochemicals) in diets containing 20% fat were investigated in weanling rats. They were fed basal 18% protein (20% casein) diets and basal diets supplemented with 0.25% L-methionine, 0.35% L-arginine or methionine + arginine for a period of four weeks. The unsupplemented basal diets contained 1.38–1.41 mg of methionine + cystine and 1.46–1.49 mg of arginine per kilocalorie and were similar in nutrient composition to those utilized for evaluation of dietary oils. The methionine and arginine supplemented diets contained 1.92–1.96 mg of methionine + cystine and 2.23±2.27 mg of arginine per kilocalorie. Dietary supplementation with methionine, arginine or methionine + arginine had no significant (P>0.05) effects on food consumption; weight gain; protein efficiency ratio; net protein ratio; liver protein utilization; or liver, heart and kidney weight in rats. These results suggest that all amino acid requirements for rat growth are met by 20% unsupplemented casein of the types tested here.