Niacin and tryptophan requirements of mule ducklings fed corn and soy-based diets

Experiments were conducted to determine the dietary niacin and tryptophan requirements of mule ducklings fed a corn-soy basal diet. In niacin requirement experiments, day-old, straight-run mule ducklings were fed diets supplemented with graded levels of niacin for 3 weeks. The results showed that the minimum niacin requirement was 45 mg/kg of the diet. For the determination of the optimal tryptophan in the diet, day-old ducklings of mixed sexes were fed a starter diet for 1 week, and then fed for 12 days experimental diets with graded tryptophan levels and containing 18.0% crude protein and 3013 kcal ME/kg. The minimum tryptophan requirement for maximum growth and feed efficiency was .23% of the diet or 1.28% of the dietary crude protein. Further experiments were performed by using a 3 (niacin 20, 50, and 80 mg/kg) x 4 (total tryptophan .13, .23, .33, and .43% of air-dried diet) factorial design to investigate the relationship between niacin and tryptophan. It was concluded that excess tryptophan could spare the ducklings' need for niacin. Conversely, excess niacin failed to compensate for a deficiency of tryptophan. Maximum growth was obtained and bowed-leg disorder was prevented by the addition of sufficient niacin or tryptophan to the basal diets.