Analgesic, hemodynamic, and respiratory effects of caudal epidurally administered xylazine hydrochloride solution in mares.

This research tests the effects of injecting a specific dose of xylazine, a sedative and analgesic, into the spine in horses. The results indicate that this procedure is safe and can successfully provide pain relief for several hours with minimal side effects.

Research Design and Methodology

The study used a randomised, blind design to measure:

• Perineal analgesia effectiveness, meaning numbness or loss of feeling in the perineal area.
• Sedation and ataxia (lack of muscle control) effects.
• Impacts on the cardiovascular (circulatory) and respiratory systems.

Eight healthy female horses (mares) were given a 0.25 mg/kg dose of xylazine, which was mixed with a sterilised 0.9% sodium chloride (NaCl) solution until the total volume was 6ml/450kg. This was then injected into the spinal canal at the sacrococcygeal joint, which is located at the base of the spine.

Blood samples were taken before and during a three-hour testing period following the xylazine administration. Various cardiovascular and systemic hemodynamic factors were measured, like cardiac output and several blood pressures.

Analysis and Results Overview

The post-treatment measurements were statistically analysed to look for significant changes and differences between:

• The control experiment with 0.9% NaCl only.
• The experiment with xylazine treatment.

These included measures of:

• Analgesia effectiveness
• Sedation levels, judged by drooping of the head (ptosis)
• Physical coordination (ataxia)
• Respiratory rates and arterial blood pressure
• Packed Cell Volume (PCV) and hemoglobin concentration – markers of anaemia and oxygen carrying capacity of the blood
• Arterial oxygen content and oxygen transport

Key Findings

The study determined that epidural injection of xylazine:

• Induced analgesia (pain reduction) from 15 minutes post-injection, which lasted for 165 to over 180 minutes.
• Caused minimal sedation and ataxia (loss of muscle coordination) in standing horses.
• Decreased heart and respiratory rates, and arterial blood pressure. These effects were not observed when the control solution was administered.
• Did not significantly change cardiac output, stroke volume, and other measures necessary for normal functioning of cardiovascular and respiratory systems.

The research concludes that xylazine can be administered epidurally at this dose for prolonged analgesia, with minimal side effects, in conscious, standing horses.