Effects of niacin status on tryptophan requirements of starter white Pekin ducks

A 4×5 factorial experiment, using 4 supplemental nicotinamide levels (0, 40, 80, and 120 mg/kg) and 5 dietary Trp levels (1.32, 1.67, 2.02, 2.37, and 2.72 g/kg), was conducted to study the effects of niacin status on Trp requirements for growth of starter white Pekin ducks from hatch to 3 wk of age. Eight hundred and forty 1-d-old male white Pekin ducks were assigned to 20 treatments with 6 replicate pens and 7 ducks per pen. All ducks were reared in raised wire-floor pens from hatch to 21d of age. No supplementation of nicotinamide in diets caused bowed leg deformity regardless of dietary Trp levels and the 40 mg and greater supplemental nicotinamide/kg completely prevented bowed leg deformity at all Trp levels. The interaction between nicotinamide and Trp influenced weight gain and feed intake of ducks (P<0.001). Supplementation of Trp in diets alleviated the depression of weight gain and feed intake caused by niacin deficiency at 0 mg supplemental nicotinamide/kg, but supplementation of nicotinamide in diets did not alleviate the depression of weight gain and feed intake caused by dietary Trp deficiency (1.32 g Trp/kg). According to the broken-line regression, the Trp requirements of starter Pekin ducks for weight gain from hatch to 3 wk of age at 0, 40, 80, and 120 mg/kg of supplemental nicotinamide were 2.42, 1.68, 1.69, and 1.69 g/kg, respectively, and the Trp requirement was much greater at 0 mg/kg of supplemental nicotinamide than at other 3 supplemental nicotinamide levels (P<0.05). In conclusion, the interaction between niacin and Trp in duck diets was supported by the effects of niacin status on Trp requirements of starter white Pekin ducks and niacin deficiency markedly increased the Trp requirements of white Pekin ducks.