Nutritional Studies with the Guinea Pig: VIII. Effect of Different Proteins, with and without Amino Acid Supplements, on Growth

Abstract

Both casein and purified soy protein produce good growth rates in young guinea pigs fed purified diets, especially if they are used in the ration at levels of 35 to 40%. To obtain a rapid rate of growth with protein levels of 30%, the casein ration must be supplemented with 0.3% arginine and the soy protein with 0.5% dl-methionine. Poor growth occurred when these proteins were used at levels of 20%. Marked improvement occurred with the addition of 1.0% of arginine to a 20% casein diet and of 1.0% methionine to a 20% soy protein diet. No further improvement occurred when methionine and tryptophan were added to the arginine-supplemented casein diet and this was also true of arginine and tryptophan added to the methionine-supplemented soy diet. Diets containing both casein and soy protein, each at a 10% level, produced better growth than when either protein was used alone at a 20% level. Supplementation of the ration containing both proteins with methionine improved the growth rate. The use of a mixture of soy protein and gelatin, each at a 10% level, produced poor growth. Addition of a mixture of the essential amino acids, except arginine and tryptophan yielded a considerable improvement in growth and with the further addition of tryptophan, a fairly good rate of growth was achieved. Substitution of an isonitrogenous amount of alfalfa for 20% of the casein of the purified diet resulted in a growth rate equal to that obtained with the commercial ration.