The effects of corticosterone (CORT) on diet selection of broiler chickens offered a choice of a high protein concentrate (381 g CP/kg, 17.5 MJ/kg ME) and whole wheat (113 g CP/kg, 15.9 MJ/kg ME) in relation to age were examined in two experiments. 2. Daily intramuscular injections of 2 and 4 mg/kg of CORT for a 5-d period in both 2- and 5-week-old chickens resulted in increases in total food, protein and energy intakes. This led to a decrease in protein accretion in older but not younger chicks, an increase in total lipid contents of the carcase at both ages, and produced changes in internal organs. 3. CORT significantly reduced body weight gain of young but not old chickens, suggesting that mature birds respond better than young ones to the physiological changes caused by treatment, by making subsequent appropriate food choices. 4. Administration of CORT in young chicks increased wheat intake at 2 and 4 h after injection, while in older birds a similar increase was maintained up to 24 h after injection. Intake of HP food was decreased by both doses of CORT in young chicks but there was no significant effect in older chickens. 5. Changes in energy: protein ratio in the chosen diet appeared at 4 h after treatment in old chickens and at 24 h in younger chicks. 6. The results suggest that birds are able to detect metabolic changes caused by CORT administration and attempt to redress them by modifying their food pattern. The time course of the response of birds to these changes is age related. However, the food selection pattern did not completely compensate for the physiological defects.
