Insulin-like growth factor-I (IGF-1) mRNA levels and chicken muscle growth.

Insulin-like Growth Factor-1 is a key regulator of muscle development and metabolism in birds and other vertebrate species. In a first part, the present paper sums up the specificities of the IGF system in birds and especially those related to muscle development. In a second part, it reviews available data obtained with avian genetic or nutritional models. Data obtained by comparing genetic models with large variations of overall body growth show a positive relation between endocrine IGF-1 and growth rate. Data obtained using both genetic and nutritional models show a positive relation between muscle IGF-1 mRNA levels, which determine paracrine IGF-1 levels, and post hatch muscle growth.