Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 1998
Publication Date: N/A
Interpretive Summary: Factors controlling lean tissue accretion and fat deposition in poultry are being elucidated. This study was conducted to ascertain whether the insulin-like growth factors, IGF-I and IGF-II, would affect protein and fat synthesis in broiler chickens, when given as a continuous infusion. IGF-I, but not IGF-II, stimulated growth and food utilization by 10-15%. Carcass fat content was reduced by IGF-I. The results of this study demonstrate that IGF-I is important to controlling growth in young chickens. The role of IGF-II in growth and metabolism remains unclear. The results of this study will be of interest to other scientists and poultry producers.
The efficacy of exogenous IGFs to stimulate growth was examined in a number of broiler chicken lines. From around 600 g body weight the chickens received a continuous infusion for two weeks of vehicle, human recombinant IGF-I or IGF-II at 300 ug/kg body weight per day or a combined infusion of 150 ug/kg/d of each IGF. Experiment 1 used commercial broiler female chickens and included measurements of nitrogen balance, N-methylhistidine excretion and muscle protein synthesis rates. In experiment 2 the same treatments were applied to three experimental lines of chickens selected for high food consumption or high food utilization efficiency. IGF-I, but not IGF-II, significantly increased growth rate and food utilization efficiency by around 10-15% in each experiment, an effect which was consistent across all genotypes. Nitrogen balance was significantly increased by IGF-I in experiment 1 as was carcass nitrogen content, indicating that the increased growth was in lean tissue. Carcass fat was consistently reduced in chickens receiving IGF-I. Protein synthesis rates were unaffected by treatment and could not account for increased growth rate. There was a significant reduction in methylhistidine excretion indicating a reduced rate of muscle protein breakdown in IGF-I treated chickens. Our results show that IGF-I may be important in controlling growth and efficiency of food utilization of young chickens at least in part by modulated the rates of protein breakdown.