Adding a local analgesic to the systemic pain medications used during castration relieved pain in colts, researchers recently reported.

The researchers observed three groups of 12 colts. All of the horses received pain medication before and after surgery. One group received butorphanol, a morphine derivative; one received phenylbutazone, an anti-inflammatory; and the third received both drugs. All of the horses also received an injection of lidocaine into each testicle at the time of castration.

The researchers assessed the horses' pain several times a day before, during, and for four days after castration by reviewing the animals' cortisol levels, pain scores, behavior, body weight, eating and drinking, gastrointestinal motility, and physical activity.

"Our study showed that when a local anesthetic like lidocaine is used under anesthesia, there is no advantage of using butorphanol over phenylbutazone," said Macarena G. Sanz, DVM, MS, Dipl. ACVIM, who was with Washington State University during the study, but is now with the University of Pretoria in South Africa