EFFICACY OF AN EPIDURAL COMBINATION OF MORPHINE AND DETOMIDINE IN ALLEVIATING EXPERIMENTALLY-INDUCED HINDLIMB LAMENESS IN HORSES

Amphotericin B-induced synovitis of the left tarsocrural joint was use d to create a grade 3 of 4 lameness in 11 horses. Caudal epidural cath eters were placed and advanced to the lumbosacral region. Baseline hea rt and respiratory rates were recorded and horses were videotaped at a walk and trot. Morphine sulphate (0.2 mg/kg) and detomidine hydrochlo ride (30 mu g/kg) were administered to treated horses (n = 8) through the epidural catheter; an equivalent volume of physiologic saline solu tion was administered to control horses (n = 3) through the catheter. At hourly intervals after epidural injection for a total of 6 hours, h eart and respiratory rates were recorded, and horses were videotaped w alking and trotting. At the end of the observation period, video recor dings were scrambled onto a master videotape. Lamenesses were scored b y three investigators unaware of group assignment or treatment time. L ameness scores, heart rates, and respiratory rates were compared betwe en groups using repeated measures analysis of variance. There was a si gnificant decrease in lameness score after treatment with epidural mor phine and detomidine (P = .0003); average lameness scores of treated h orses were less than grade I at each hourly observation for 6 hours af ter drug administration. Early in the observation period, heart rates significantly increased in control horses and decreased in treated hor ses (P = .03). A similar trend occurred for respiratory rates (P = .07 ). Results of this study demonstrate that epidural administration of a combination of morphine and detomidine is capable of providing profou nd hindlimb analgesia in horses. (C) Copyright 1996 by The American Co llege of Veterinary Surgeons