Perspectives on the endocrinology of poultry growth and metabolism

Abstract Birds have rapid pre- and post-hatching growth rates. The major hormones required to support normal growth are growth hormone (GH), triiodothyronine (T3 ) and insulin-like growth factor-I (IGF-I). Optimal growth requires a “set-point” concentration of both IGF-I and T3 in the circulation. Pituitary GH plays a role in controlling the circulating concentrations of both IGF-I and T3 . Nutritional restriction (energy, protein) leads to reductions in circulating concentrations of both IGF-I and T3 with increased GH secretion due removal of negative feedback. Similarly, there is un-coupling of the GH–IGF-I axis in stunting disease. A critical control point is at the level of the liver and GH receptor/signal transduction. The major hormones controlling metabolism include glucagon, insulin, adrenal glucocorticoid hormone, corticosterone and potentially somatostatin. Chickens and turkeys have higher circulating concentrations of glucose than those of livestock mammals. What are not known include the following: the biological basis for the high basal glucose concentrations; the quantitative fluxes of key metabolites in the fed and fasted state through growth and development; the relative contribution of different organs to gluconeogenesis; the relative importance of insulin and somatostatin in controlling lipolysis and the role of gastro-intestinal hormones in the control of metabolism.