Nutritional and developmental roles of insulin-like growth factors in poultry.

Insulin-like growth factor-I and -II are important multifunctional polypeptides that interact with membrane-bound receptors as well as soluble binding proteins. The biological actions of these hormones are multifaceted and dependent to a large extent on binding protein interactions. Some unique differences in insulin-like growth factor physiology and biochemistry are evident between mammalian and avian species. These include amino acid compositional and significant receptor differences as well as binding protein status. The biological response to both growth factors is different in birds. A greater proportion of the insulin-like growth factors exists in plasma as free peptide compared with the situation in mammals. This review is a brief summary of our knowledge of insulin-like growth factor physiology in domestic fowl.