Response of broilers and capons to heat stress following adrenal manipulation

Five-week-old capons and normal broiler males were used in an experiment to test the effect of caponization and adrenal cortical manipulation on subsequent heat stress survival. Saline, adrenocorticotropin (ACTH) at 20 IU/kg, or metyrapone at 60 mg/kg was given daily at either 0730 or 1400 hr. No differences attributable to the time of injection were found. Prestress weights for all groups were not significantly different. Capons and sham-operated males receiving either the vehicle or metyrapone showed significantly higher heat stress mortality (P less than .01) than capons receiving ACTH. This suggests an important adrenal contribution in the ability of young chickens to withstand high environmental temperatures. The results also indicate that the susceptibility of male broilers to heat stress is not directly related to the testes.