Effect of Xylazine and Butorphanol on Experimental Hind Limb Lameness in Horses

Abstract Anesthetic blocks of hind limbs play a fundamental role in the diagnosis of conditions affecting these sites. However, some restless horses can make this procedure much more difficult. Many clinicians believe that the use of chemical restraint to facilitate joint injections may interfere with the lameness intensity. This study aimed to assess whether sedation with xylazine hydrochloride alone or associated with butorphanol tartrate ameliorate or even abolish induced hind limb lameness. Intravenous injection of xylazine (0.3 mg/kg) alone (XG) or associated with butorphanol (0.01 mg/kg) (XBG) were given randomly to 16 adult horses. A third control group (CG) was left untreated. All horses participated in all groups. Lameness induction was performed with the placement of a circumferential metal clamp causing pressure on the hoof wall. Sedation was assessed using a descriptive physical and behavioral scale and by the head height above ground (HHAG) before the treatment (0 minutes) and 20, 30, and 40 minutes following treatment. Objective lameness evaluations were performed before sedation (after lameness induction) and at 20, 30, and 40 minutes postsedation. There was no difference in pelvic asymmetry between xylazine, xylazine with butorphanol, and untreated control group at the different evaluation times. Spearman's correlation showed that there was no correlation between the factors HHAG and LI ( r s  = 0.148). Xylazine alone or associated with butorphanol at the recommended doses may be used as chemical restraint to turn an anesthetic block of the hind limbs into a safer procedure without masking lameness intensity for at least 40 minutes postadministration.