Effects of gonadal steroids and adrenergic agonists on avian growth and feed efficiency.

The effects of gonadal steroids and adrenergic agonists in growing poultry are reviewed. Estrogens, used commercially to caponize, improve muscle palatability and weight gain but are hyperlipidemic and adversely affect feed efficiency. Their ability to caponize results from the fact that negative feedback regulation of gonadotropin secretion is mediated by estrogen synthesized within the male's central nervous system. Androgens are strongly anabolic in avian species but are deleterious to growing bone. Thus, androgens depress growth and efficiency when given before epiphyseal closure but stimulate gain and improve efficiency when given afterwards. The beta-adrenergic agonist clenbuterol improves the growth and efficiency of broiler chickens. The effects of beta-agonists on muscle, adipogenic tissue, and the endocrine system are presented as possible mechanisms for these actions.