Evaluation of the effects of commonly used α-adrenergic receptor agonists alone and in combination with butorphanol tartrate on objective measurements of lameness in horses.

OBJECTIVE

To determine the effects of 3 α-adrenergic receptor agonists (α-ARAs), alone or in combination with butorphanol tartrate, on objective measurements of lameness in horses.

ANIMALS

17 adult polo horses with naturally occurring forelimb or hind limb lameness (or both).

PROCEDURES

In a crossover design, each horse received each protocol (saline [0.09% NaCl] solution [2 mL, IV] or xylazine hydrochloride [0.33 mg/kg, IV], detomidine hydrochloride [0.007 mg/kg, IV], or romifidine hydrochloride [0.033 mg/kg, IV] alone or in combination with butorphanol [0.007 mg/kg, IV]) in random order, with a washout period (≥ 7 days) between protocols. Horses were assessed immediately prior to (baseline) and 10, 15, 20, 30, and 40 minutes after administration of each protocol for degree of sedation, mechanical nociceptive threshold (MNT), and objective lameness measurements.

RESULTS

Compared with baseline values, sedation scores and MNTs were significantly higher at all evaluated time points following administration of all sedation protocols except xylazine alone; following administration of xylazine alone, sedation scores and MNTs were significantly higher at ≤ 30 minutes and ≤ 20 minutes, respectively. Significant differences in objective forelimb lameness measurements were noted after administration of the 3 α-ARA-butorphanol combinations. Most significant differences in objective measurements of hind limb lameness were detected after administration of detomidine or romifidine, alone or in combination with butorphanol.

CONCLUSIONS AND CLINICAL RELEVANCE

In the study horses, xylazine alone had the least impact on objective lameness measurements. The administration of α-ARAs, particularly detomidine or romifidine, alone or in combination with butorphanol, resulted in small but significant effects on objective lameness measurements.