Perineal analgesic actions of epidural clonidine in cattle.

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

Study Design: Prospective randomized study.

Animal Population: Six healthy male cattle weighing between 236 and 365 kg.

Methods: To investigate the effect of epidural clonidine, the animals received 2 and 3 micro g 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.

Results: 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 microg kg(-1) versus the 2 microg 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.

Conclusions: Epidural administration of 2 and 3 micro g kg(-1) of clonidine in cattle in this study provided bilateral perineal analgesia/anesthesia with a dose-dependent onset and duration of action.

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