Peripheral regulation of food intake in poultry.

This review focuses on food intake regulation in avian species with the emphasis on sites of action outside of the central nervous system using data obtained mainly with studies involving poultry. Avian species do appear to regulate food intake, and there is good evidence that both the gastrointestinal tract and the liver are primary sites for regulation. Although young meat-type chickens may be eating near gut capacity, this does not appear to be the case in older birds. Furthermore, although the crop probably has a role in food intake control when meal feeding, its role during free access feeding is marginal. Food intake can be altered in chickens by infusion of glucose, lipids, epinephrine and possibly amino acids into the liver. The response to such infusions is altered by genotype and feeding state (fed or unfed). In addition, injection of peptides including cholecystokinin, bombesin, and gastrin outside the central nervous system decrease food intake. It is uncertain whether the anorexigenic effect of these peptides is a specific response, or if it is a general response caused by abdominal discomfort. Opioids appear to stimulate food intake with at least part of their effect being from outside of the central nervous system. Therefore, although the central nervous system is involved in food intake control in avian species, there are other sites involved. Furthermore, genetic selection for growth in meat-type chickens has altered the responsiveness of these control mechanisms suggesting that there is genetic variation for these physiological systems.