Adrenocortical Response in Cows after Injection of Adrenocorticotropic Hormone

Adrenocorticotropic hormone (ACTH) challenge test is recognized as a method for evaluating some forms of stress. Six lacting cows, well trained to blood sampling were used for this study. Cows were randomly assigned to receive saline or an intramuscular single dose (0.5 μg/kg) of ACTH (Synacthen Depot). Blood samples (10 mL) were collected from the coccygeal blood vessels of all cows at 0 h (immediately before treatment) and every 30 min for 2 h to measure serum cortisol, glucose, creatinine and urea concentrations. Each blood collection included a separate puncture of the coccygeal blood vessels using a new needle. Respiratory frequency was measured for each cow at 0, 30, 60, 90 and 120 min. Serum cortisol concentrations of cows did not differ between treatments at the initiation of treatments; however, serum cortisol, glucose, creatinine, urea concentrations and respiratory frequency were affected by ACTH, time, and the interaction of ACTH x time. Administration of ACTH increased (P < 0.05) serum cortisol concentration in cows within 30 min of administration, and concentrations remained increased throught the blood sampling period. Cows that received ACTH had increased (P < 0.05) respiratory frequency within 30 min of administration. An increase in hypothalamic pituitary-adrenocortical activity, causes the rise of blood cortisol, indicates a physiological response to different stressors.