Evaluation of the analgesic effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H in horses.

Objective—To evaluate and compare effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H on avoidance threshold to noxious electrical stimulation over the dermatomes of the perineal, sacral, lumbar, and thoracic regions in horses. Animals—5 healthy adult horses. Procedure—Using a Latin square complete repeatedmeasures design, horses were randomly assigned to receive 1 of 6 treatments (morphine, alfentanil, butorphanol, tramadol, U50488H, or sterile water) at intervals of at least 7 days. Agents were injected epidurally at the first intercoccygeal epidural space, and electrical stimulation was applied at repeated intervals for 24 hours to the dermatomes of the perineal, sacral, lumbar, and thoracic regions. Avoidance threshold to electrical stimulation was recorded. Results—Administration of butorphanol, U50488H, and sterile water did not induce change in avoidance threshold. Alfentanil increased avoidance threshold during the first 4 hours, but not significantly. Trama...