The Tryptophan Requirement of the Young Pig

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Abstract
Young pigs weighing approximately 30 lb. were employed to determine the tryptophan requirement and the effect of dietary protein level, as zein, and dietary antibiotics thereon. Diets formulated largely with yellow corn and menhaden fish meal and containing 15.4 percent protein were deficient in tryptophan to support normal performance during a four-week period. Additional protein in the diet, added as 5 percent zein, failed to improve rate or efficiency of gain or to affect the response to supplementary levels of L-tryptophan. In the presence of adequate nicotinic acid the minimum L-tryptophan requirement of the weanling pig is 0.1 IS percent of a diet containing 15.3 percent protein. Addition of DL-tryptophan to a deficient diet improved rate of gain, although it had no effect on the yield or specific gravity of the carcass produced. However, the thyroid gland when expressed as a percentage of the carcass weight was significantly larger in the tryptophan-deficient pig. The feeding of a mixture of antibiotics failed to influence thyroid gland weight, although the pigs exhibited improvement in rate and efficiency of gains. Evidence was obtained that the pig can utilize the D-tryptophan present in a racemic mixture.