EquineReview

The ability to localise lameness in horses using diagnostic analgesia is incredibly useful and forms the bedrock of a thorough lameness workup. However, anyone involved in the placement of nerve blocks will know how challenging, and at times dangerous, this can be. Historically the use of sedation to facilitate placement of nerve blocks was thought to affect the interpretation of the block through its analgesic effect. Equally, assessment of an excitable horse can be challenging and administration of sedation or tranquilisation may be necessary to allow safe and accurate assessment when trotted in hand. Morgan et al (Equine Vet J. doi: 10.1111/evj.13225) have compared the effect of xylazine (0.1–0.2 mg/kg intravenously (IV)), acepromazine (0.02 to 0.04 mg/kg IV) and IV saline when administered to six lame horses. Lameness was induced with set screws in a custom-made shoe and the study was a randomised crossover design. Horses were assessed at 10, 30, 45 and 60 minutes after treatment using both subjective assessment and inertia sensors. No significant difference was seen in the level of lameness, either objectively or subjectively, for any treatment group compared with the saline control. In addition, significant sedation-induced ataxia was not observed. A reduced stride rate was seen throughout the 60-minute period of the study following acepromazine administration; this was not seen with xylazine. In individual observers, acepromazine induced variable changes in subjective lameness grade. This manifested in a decrease in lameness grade after high-dose acepromazine was administered with one observer, and an increase in lameness grade following lowdose acepromazine administration with another observer. In conclusion, the study supports the use of low-dose acepromazine or xylazine to facilitate forelimb lameness evaluation. This should be considered both in calming an excitable horse, causing it to trot more consistently, and to reduce movement during placement of nerve blocks.