Model of physiological stress in chickens 4. Digestion and metabolism

Two similar experiments were conducted to evaluate the effects of stress on growth and feed utilization of broiler chicks. Stress was induced by continuous delivery of adrenocorticotropin (ACTH) at 8 IU/kg BW/d for 7 consecutive d. During the 7-d stress period, ACTH-treated chicks did not exhibit increases in feed intake, but increases in water intake concomitant with an increase in excreta output were recorded. The ACTH caused decreases in digestion of dry matter, proteins, gross energy, and carbohydrates, whereas fat digestibility was unaffected. Digestion of these nutrients was affected more than absorption during the stress period. By 1 wk poststress, all parameters were comparable with those of the control, except for feed intake, which was less than that of CON. The BW of ACTH-treated chicks were lower than CON through 1 wk after cessation of infusion of ACTH. Contrasted to effects during the stress period, after cessation of ACTH-treatment, absorption of all nutrients was reduced, and, during this poststress recovery period, digestion appeared to return to the range of CON values. Results indicate that all physiological parameters with the exceptions of reductions in BW and thymus weight returned to the range of CON values within 1 wk after cessation of ACTH infusion. However, feed intake and absorption of energy dry matter and nitrogenous compounds remained lower than CON at that time. Also, losses in skeletal muscle caused by prolonged gluconeogenesis apparently required extended periods for complete recovery, as evidenced by stressed chicks that did not gain comparably to CON after a 1 wk cessation of ACTH delivery.