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 insulin-like growth factor-I (IGF-I) concentrations in Pekin ducks. Plasma IGF-I in Pekin ducks was assayed in a heterologous radioimmunoassay for human IGF-I. When treated with acid, the response dose of duck IGF-I was parallel to that of human recombinant (r) IGF-I. The effect of line (greater breast muscle thickness vs control) was determined in Experiment 1 in female ducks. The ducks with greater breast muscle thickness had higher (P < 0.05) plasma 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. Three 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. Males exhibited higher (P < 0.05) IGF-I than females. Plasma IGF-I concentrations decreased with age from 42 to 49 d. In Experiment 3, the effects of selection criterion thigh or low breast muscle thickness to total breast thickness ratio) and the feed-deprived or fed state were studied in female Pekin ducks. The high ratio ducks were more affected by feed deprivation. These ducks had similar plasma IGF-I concentrations to low ratio ducks during feed withdrawal, but had higher (P < 0.05) concentrations when fed. These data contribute to an understanding of the influence of IGF-I on metabolism and will be of value to the improvement of lean Pekin duck production.