Cortisol responses to physical and pharmacological stimuli in heifers

The aim of this study was to assess bovine plasma cortisol response to blood sampling, to 5-min isolation in a novel arena and to dexamethasone blockade and ACTH stimulation. Twelve 10-month old heifers of the Friesian and Salers breeds were used. Blood collection, carried out via a jugular cannula or caudal venipuncture, had no significant effect on cortisol level. This level increased by about 20 ng/ml 10 min after the heifers were isolated in the novel arena, and it returned to the initial value within 70 min. Cortisol response at 10 min was a good indicator of overall response and was also related to the animal remaining motionless in the arena. The cortisol level declined 14 hrs after dexamethasone injection. Intramuscular or intravenous administration of ACTH resulted in a large increase (maximum: 44 ng/ml above the initial level), and high levels were maintained from 30 to 180 min following injection. The cortisol level at 30 min seemed to be a reliable indicator of mean response to ACTH.