The Nutrition of the Newborn Dairy Calf. II. Effect of Dietary Tryptophan on the Urinary Excretion of Niacin and its Metabolites by Young Dairy Calves

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Abstract
Five g. of tryptophan were fed daily for 3 days to each of 2 dairy calves that had been maintained from birth on a whole milk diet. The amount of urinary excretion of nicotinic acid and its derivatives and tryptophan was detd. on 24-hr. samples and compared with similar data obtained previous to and following the tryptophan feeding. Tryptophan feeding resulted in a 3- to 4-fold increase in the excretion of total free and combined nicotinic acid. There was little change in the excretion of free nicotinic acid and N1-methylnicotinamide. The major portion of the increase was in the non-methylated products. The data indicate that N1-methylnicotinamide was not the main metabolic product excreted by calves. The urinary excretion of tryptophan accounted for only 1-1.5% of the intake. Increase in dietary tryptophan results in increased urinary excretion of total nicotinic acid, indicating that tryptophan serves as a precursor of niacin in the young calf as in other mammals thus far studied.