Insulin-like growth factor (IGF)-I and IGF-binding activity in normal and fast-growing chickens

Insulin-like growth factor(IGF)-binding activity were characterized in sera normal, fast growing, and very fast growing chicken strains. In contrast to a previous report, specific IGF-binding activity was observed in this nonmammalian species. Age-related IGF-binding activity levels did not differ between strains. IGF-I levels were significantly higher for the normal as compared to the 2 fast growing strains. Chromatographic studies show that IGF-I is associated with acid-dissociable high MW complexes in chicken serum, and the MW patterns are similar to human serum. Circulating levels of IGF-I or IGF-binding activity do not account for accelerated somatic growth in inbred large-bodied chicken strains.