Comparison of antinociceptive, cardiovascular, and respiratory effects, head ptosis, and position of pelvic limbs in mares after caudal epidural administration of xylazine and detomidine hydrochloride solution.

The research compares the effects of two drugs, xylazine and detomidine, when administered to horses for inducing analgesia or pain relief. The study finds that the administration of xylazine resulted in longer pain relief and fewer side effects in terms of cardiovascular and respiratory depression, head dropping, and changes in stance.

Study Design and Methodology

• The study was conducted using 8 healthy mares.
• To assess the drugs’ effects, the researchers measured several factors like the lack of sensory perception to electrical stimulation and needle prick stimulation, changes in the position of pelvic limbs, and head ptosis.
• Cardiovascular and respiratory function measurements were determined using blood samples and systemic hemodynamic testing, which included cardiac output and different arterial pressures.
• Statistical analysis was performed using a two-way ANOVA to detect significant differences between the before and after conditions for each measurement parameter.

Results

• Epidural administration of xylazine and detomidine brought about perineal analgesia, but the effects varied.
• Xylazine induced analgesia from the coccyx to the S3 dermatome with minimal cardiopulmonary depression, head ptosis, changes in the pelvic limb position, and no urination observed in standing mares.
• Detomidine induced analgesia ranging from the coccyx to either the S3 or T15 dermatome, but it caused cardiovascular depression, pronounced head ptosis, limb position changes, and diuresis or increased urination in standing mares.
• The onset of analgesia after the administration of xylazine and detomidine was approximately 13.1 and 12.5 minutes, respectively.
• The duration of analgesia was significantly longer for mares after xylazine administration, lasting from 165 to over 180 minutes, compared to around 160 minutes for detomidine.

Conclusions

• Based on the results, xylazine administration (0.25 mg/kg of body weight in 8 ml of 0.9% NaCl) via the caudal epidural route is found to provide the most favorable conditions.
• It provided a long-lasting perineal analgesia of over 2.5 hours, with minimal cardiovascular and respiratory depression, changes in pelvic limb position, and no observed urination in standing mares over a 3-hour test period.

In conclusion, xylazine is deemed safer and more effective overall for inducing analgesia in mares compared to detomidine due to its superior analgesic properties and lesser side effects.