Influence of caudal epidural analgesia on cortisol concentrations and pain-related behavioral responses in mares during and after ovariectomy via colpotomy.

Objective: To determine the influence of epidural detomidine and morphine on serum corticosteroid concentrations and pain-related behavioral responses in mares during and after ovariectomy via colpotomy. Study design: Blinded prospective study. Animals: Nine university-owned mares. Methods: Five of 9 horses received caudal epidural detomidine hydrochloride (0.01 mg/kg) and morphine sulfate (0.1 mg/kg) prior to surgery. All horses received local anesthetic around the ovarian pedicle, 0.02 mg/kg butorphanol IV at the start of the procedure and after first ovary removal, were sedated as required throughout the procedure, and were monitored for leg lifting, grunting, and abdominal tensing. Horses were monitored hourly for pain postoperatively. Heart rate was recorded every 4 hours, and photographs were taken to assess pain according to the horse grimace scale (HGS). Control group horses (n=4) were treated with butorphanol (0.02 mg/kg IV) every 4 hours for 24 hours postoperatively. All horses received oral phenylbutazone 18 hours postoperatively. Serum cortisol was measured prior to the procedure, after first and second ovary removal, and 8 and 24 hours postoperatively. Results: No differences were detected between horses receiving caudal epidural detomidine and morphine and those that received systemic opioids. A decrease in HGS score occurred after phenylbutazone administration. Conclusion: Administration of caudal epidural detomidine and morphine resulted in similar pain-related behavior and corticosteroid concentrations as did administration of systemic butorphanol every 4 hours for 24 hours postoperatively.