Model of physiological stress in chickens 2. Dosimetry of adrenocorticotropin

Continuous adrenocorticotropin (ACTH) delivery by mini-osmotic pumps is a r eliable method to induce stress in broilers. The present study was conducte d to determine the minimum effective dose of ACTH that will evoke physiolog ical stress. Chicks, which had been reared under floor-pen conditions until 5 wk of age received mini-osmotic pumps by surgical implantation. The mini -osmotic pumps delivered 2, 4, 8, or 16 IU of porcine ACTH/kg BW/d for 7 co nsecutive d. Controls (CON) were untreated chicks. Continuous infusion of A CTH caused dose-related stress responses. Chicks that received 8 or 16 IU s howed the greatest responses, whereas those that received 2 or 4 IU were in termediate to the birds dosed with high ACTH and the CON birds. Responses i ncluded decreased BW; decreased relative weights of the bursa of Fabricius, thymus, and spleen; and increased relative liver weight. Concomitantly, in creased liver lipid and decreased liver moisture were recorded. Plasma conc entrations of corticosterone (CS), glucose (GLU), total protein (TP), chole sterol (CHOL), and triglycerides (TRI) and the ratio of heterophils to lymp hocytes were increased during ACTH infusion. ACTH infusion at 8 IU/kg BW/d for 7 d was determined to be the minimum effective dose that caused physiol ogical stress in broilers.