Effects of line, dietary protein, sex, age, and feed withdrawal on insulin-like growth factor-I in white Pekin ducks

Three experiments were conducted to determine and characterize plasma insul in-like growth factor-I (IGF-I) concentrations in Pekin ducks. Plasma IGF-I in Pekin ducks was assayed in a heterologous radioimmunoassay for human IG F-I. When treated with acid, the response dose of duck IGF-I was parallel t o that of human recombinant (r) IGF-I. The effect of line (greater breast m uscle thickness vs control) was determined in Experiment 1 in female ducks. The ducks with greater breast muscle thickness had higher (P < 0.05) plasm a IGF-I concentrations than the control ducks. Ln Experiment 2, the effects of dietary protein, sex, and age were examined from 42 to 49 d of age. Thr ee dietary programs that differ in dietary crude protein were used in this experiment. Ducks on the high protein program had (P < 0.05) higher plasma IGF-I concentrations than ducks on either medium or low protein programs. M ales exhibited higher (P < 0.05) IGF-I than females. Plasma IGF-I concentra tions decreased with age from 42 to 49 d. In Experiment 3, the effects of s election criterion thigh or low breast muscle thickness to total breast thi ckness ratio) and the feed-deprived or fed state were studied in female Pek in ducks. The high ratio ducks were more affected by feed deprivation. Thes e ducks had similar plasma IGF-I concentrations to low ratio ducks during f eed withdrawal, but had higher (P < 0.05) concentrations when fed. These da ta contribute to an understanding of the influence of IGF-I on metabolism a nd will be of value to the improvement of lean Pekin duck production.