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

Abstract

Following the reports (6, 7) that tryptophan can replace niacin in affecting growth of laboratory animals on niacin-deficient rations, various investigators determined the effects of dietary tryptophan on the excretion of niacin and its metabolic products not only in the rat (10, 13) but also in the pig (8), horse (12) and man (11). In all cases the feeding of tryptophan resulted in a marked increase in the excretion of these substances, indicating a metabolic relationship between tryptophan and niacin. The nature and concentration of the excreted products suggest that there is a species variation in this respect. It has been found that there are large increases in the excretion of Nl-methylnicotinamide when tryptophan is fed to rats (13), pigs (8) and humans (11), whereas in the case of the horse (12), there is no significant increase in the excretion of this substance but an increase in free nicotinic acid and other non-methylated products.