EFFICIENCY OF TRYPTOPHAN-NIACIN CONVERSION IN CHICKENS AND DUCKS

Experiments were conducted with Pekin ducklings, mule ducklings and br oiler chicks to determine the efficiency of conversion of tryptophan t o niacin. When chicks were fed a diet marginal in tryptophan and defic ient in niacin, either tryptophan or niacin supplementation improved g rowth and prevented niacin deficiency symptoms. However, only niacin i mproved growth and prevented symptoms in Pekin or mule ducklings. Live r 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-hydr oxyanthranilic acid oxygenase (3-HAAO) activity to PAC activity in liv er were significantly influenced by tryptophan or niacin in the diet i n chicks but not in ducks. The efficiency of conversion of tryptophan to niacin was calculated from the relative responses in weight gains w hen 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 equiv alent to 1 mg of niacin in Pekin ducklings, mule ducklings and broiler chicks, respectively. The duckling has a limited ability to use trypt ophan to spare niacin.