The effect of food intake from two weeks of age to sexual maturity on plasma growth hormone, insulin-like growth factor-I, insulin-like growth factor-binding proteins, and thyroid hormones in female broiler breeder chickens.

Plasma concentrations of metabolic hormones were determined in broiler breeders fed on three quantitatively different food regimes in the period prior to sexual maturity. The first group was fed ad libitum, the second group was fed a restricted quantity of food, and the third group was restricted to obtain an intermediate body weight between those of the first two groups. In food-restricted birds, insulin-like growth factor-I (IGF-I) reached the highest plasma concentrations at 8 and 14 weeks of age in contrast with levels in the fully fed animals, in which only one maximum value was observed at 10 weeks. From 14 weeks on, IGF-I concentrations remained higher in the restricted groups compared to the ad libitum group. Three IGF-binding proteins with molecular masses of 28, 34, and 40.5 kDa were detected in the plasma of broiler breeders after Western ligand blotting. The concentrations of the 28- and 34-kDa IGF-binding protein bands showed an age-related pattern in all groups. The intensity of these bands was higher in the restricted groups compared to that of the bands for the fully fed animals. No significant differences between the groups could be observed in the intensity of the 40.5-kDa band. Food restriction resulted in higher plasma concentrations of GH and T4 compared with levels in the fully fed animals. T3 plasma concentrations were higher in the ad libitum fed group than in the restricted groups. In all groups, GH and T3 concentrations decreased with advancing age, whereas T4 increased during the same period. This is the first description of the effects of long-term food restriction prior to the onset of sexual maturity on circulating levels of hormones of the somatotrophic and the thyrotrophic axes in female broiler breeders. The interrelationship between GH, IGF-I, IGFBPs, and thyroid hormone concentrations and differences in subsequent reproductive performance of differently fed broiler breeders requires further investigation.