Some Effects of DL-Methionine and Glycocyamine on Growth and Nitrogen Retention in Rats

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Abstract
Nitrogen retention and growth by weanling rats pair-fed a 12% casein diet containing 1% of methionine and 1% of glycocyamine was significantly increased above that of the controls fed 12% casein alone or with a 1% DL-methionine supplement. The excretion of urea plus ammonia nitrogen was approximately the same for all groups. The inclusion of 1% of methionine in a 12% casein diet fed ad libitum increased the growth rate, but the addition of 1% glycocyamine increased growth rate (and food efficiency) even further. The use of 1% of DL-methionine with 2, 3 or 4% glycocyamine reduced growth rate below this high value, although it remained above that of the controls. Although the rate of growth did not increase above that of the controls when 2% of methionine was added to the diet, this amount of methionine did overcome the reduction in growth rate noted when glycocyamine alone was added in 1, 2, 3 or 4% quantities to the basal diet. Food efficiencies were found to parallel weight gains on the various diets. Animals fed the basal diet with 1% of DL-methionine and 1% of glycocyamine showed the highest food efficiency. These observations suggest that methionine not only can overcome the toxic effects of glycocyamine, but that if both are added in metabolically balanced quantities to a 12% casein diet, there is a significant increase in weight gain, food efficiency and nitrogen retention over that of any of the diets tested.