Perineal analgesic actions of epidural clonidine in cattle

To determine the analgesic, sedative, motor, cardiac and respiratory effects of epidural clonidine in cattle.

Prospective randomized study.

Six healthy male cattle weighing between 236 and 365 kg.

To investigate the effect of epidural clonidine, the animals received 2 and 3 μg kg^-1 of clonidine diluted to 8 mL with 0.9% saline. Two treatments were utilized as controls. The animals from the first control treatment received 2% lidocaine (0.4 mg kg^-1) and those from the second received an equal volume of 0.9% saline. Each animal received each treatment in random order. Evaluations of analgesia, sedation, muscle relaxation, heart rate, respiratory rate and rectal temperature were obtained at 0 (basal), 2, 5, 10, 15 and 30 minutes after epidural injection, and then at 30-minute intervals until loss of analgesia occurred. All the animals received a standard noxious stimulus consisting of needle insertion into the skin and deep muscle; a 4-point scale was used to score the response. A second scale was used to score sedation and a third for muscle relaxation.

Both doses of clonidine were effective in producing analgesia of the tail, perineum, and upper hindlimb. Complete analgesia was present before (mean ± SE = 9 ± 4 vs. 19 ± 9 minutes) and lasted longer (311 ± 33 vs. 192 ± 27 minutes) for the 3 μg kg^-1versus the 2 μg kg^-1 dose, respectively. A dose-dependent sedative effect of clonidine was also observed, with a peak effect between 60 and 180 minutes. No effects on heart or respiratory rates were observed with either dose of clonidine.

Epidural administration of 2 and 3 μg kg^-1 of clonidine in cattle in this study provided bilateral perineal analgesia/anesthesia with a dose-dependent onset and duration of action.

Further studies are required to determine whether the analgesia is sufficient for surgery.