Efficiency of tryptophan-niacin conversion in chickens and ducks

Abstract

Experiments were conducted with Pekin ducklings, mule ducklings and broiler chicks to determine the efficiency of conversion of tryptophan to niacin. When chicks were fed a diet marginal in tryptophan and deficient in niacin, either tryptophan or niacin supplementation improved growth and prevented niacin deficiency symptoms. However, only niacin improved growth and prevented symptoms in Pekin or mule ducklings. Liver picolinic acid carboxylase (PAC) activity was 4 to 5 times higher in ducklings than in chicks. The activity of PAC and the ratio of 3-hydroxyanthranilic acid oxygenase (3-HAAO) activity to PAC activity in liver were significantly influenced by tryptophan or niacin in the diet in chicks but not in ducks. The efficiency of conversion of tryptophan to niacin was calculated from the relative responses in weight gains when graded levels of tryptophan or niacin were added to the diet. The results indicate that 181 mg, 172 mg and 47 mg of tryptophan are equivalent to 1 mg of niacin in Pekin ducklings, mule ducklings and broiler chicks, respectively. The duckling has a limited ability to use tryptophan to spare niacin.