THE EFFECT OF FOOD-INTAKE FROM 2 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 pe riod prior to sexual maturity. The first group was fed ad libitum, the second group was fed a restricted quantity of food, and the third gro up 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 1 4 weeks of age in contrast with levels in the fully fed animals, in wh ich only one maximum value was observed at 10 weeks. From 14 weeks on, IGF-I concentrations remained higher in the restricted groups compare d to the ad libitum group. Three IGF-binding proteins with molecular m asses of 28, 34, and 40.5 kDa were detected in the plasma of broiler b reeders after Western ligand blotting. The concentrations of the 28- a nd 34-kDa IGF-binding protein bands showed an age-related pattern in a ll groups. The intensity of these bands was higher in the restricted g roups compared to that of the bands for the fully fed animals. No sign ificant differences between the groups could be observed in the intens ity of the 40.5-kDa band. Food restriction resulted in higher plasma c oncentrations of GH and T-4 compared with levels in the fully fed anim als. T-3 plasma concentrations were higher in the ad libitum fed group than in the restricted groups. In all groups, GH and T-3 concentratio ns decreased with advancing age, whereas T-4 increased during the same period. This is the first description of the effects of long-term foo d restriction prior to the onset of sexual maturity on circulating lev els of hormones of the somatotrophic and the thyrotrophic axes in fema le broiler breeders. The interrelationship between GH, IGF-I, IGFBPs, and thyroid hormone concentrations and differences in subsequent repro ductive performance of differently fed broiler breeders requires furth er investigation. (C) 1997 Academic Press.