|Tomas, Frank - COOP. RES. CTR, AUSTRALIA|
|Pym, Robert - UNIV. OF QUEENSLAND, AUST|
|Francis, Geoffrey - COOP. RES. CTR. AUSTRALIA|
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.
Technical Abstract: 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.