Comparative study of epidural xylazine or clonidine in horses.

This study compares the cardiorespiratory and behavioral effects of two drugs — epidural xylazine (XYL) and clonidine (CLO) — when administered to horses. The findings indicate that both medications produce similar effects, but neither is considered safe to use clinically at the tested doses due to associated risks and side-effects.

Objective and Methods

• The research sought to analyze the effects of epidural XYL and CLO in horses. It was conducted as a blinded, randomized study involving twelve healthy Arabian yearling horses randomly distributed between two groups; one was administered XYL (n = 6) and the other received CLO (n = 6).
• An epidural catheter, used for the drug’s administration, and a facial arterial catheter were placed on the horses. Their restraints occurred a day later for the data collection phase.
• Baseline values of heart (HR) and respiratory (RR) rates, arterial pressure, and behavioral responses were observed and recorded prior to the epidural injection (T0) and at several intervals post-injection; specifically after 10, 20, 30, 45, 60, 90, and 120 minutes (T10-T120).
• The horses were injected with either 0.2 mg kg(-1) of XYL or 5 microg kg(-1) CLO, adjusted with saline according to the equation (3.4 + body weight in kg x 0.013) mL.
• Data analysis involved the Kolmogorov-Smirnov test, a one-way analysis of variance (ANOVA) with repeated measures, and a one-way ANOVA supplemented with a Student-Newman-Keuls test or Fisher’s exact test, as required. Significance was assigned at p <= 0.05.

Key Results

• Adverse effects such as sedation, ataxia (loss of control of body movements), and in some cases, recumbency (lying down) were observed at certain time points in both groups of horses. Penile prolapse occurred in most male horses at certain intervals, resolving by T120.
• Tail relaxation was present in all XYL horses and some CLO horses throughout the observation period. A head drop was observed from T20 to T60 in XYL horses, extending to T120 in CLO-administered horses.
• A significant decrease in respiratory rates happened only at T45 in the CLO group. Meanwhile, there was no significance in changes to heart rates and arterial blood pressures in any group.

Conclusions

• The research concluded that epidural administration of both CLO and XYL triggers similar cardiorespiratory and behavioral changes in horses. However, due to the adverse effects observed, neither drug would be safe for clinical use at the doses administered in this particular study.