Clinical actions of intramuscularly clonidine in cattle

To determine the sedative and antinociceptive effects of three doses of intramuscularly (IM) administered clonidine, an alpha-2 agonist, six healthy cattle were used in a randomized study. Each animal was treated on three occasions with intramuscular clonidine at either 4 (CL4), 5 (CL5) or 6 (CL6) meg/kg bodyweight, Sedation, antinociception, heart rate, arterial blood pressure, respiratory rate and rectal temperature were measured immediately prior (Time 0) and at 5, 10, 15, 30, 60, and every 60 minutes until animals returned to normal alertness after clonidine administration. Serum glucose concentration was measured at time 0, 30, 60 minutes and every 120 minutes. The degree of sedation and antinociception was assessed subjectively by the same observed blinded for all treatments. The three doses produced dose dependent sedation and antinociception; the highest dose induced the most prolonged sedation (approximately 405 min) and antinociception (approximately 210 min). Heart and respiratory rates decreased significantly from baseline after each treatment but blood pressure was not affected significantly. Hyperglycaemia was recorded with all doses. The results suggest that IM administration of clonidine induces dose-dependent onset and duration of sedation and antinociception in cattle and all doses induced bradycardia and a decreased respiratory rate with little interference with arterial blood pressure.