Effects of injection of botulinum toxin type B into the external anal sphincter on anal pressure of horses.

The research conducted investigates the effects of injecting Botulinum toxin type B (BTB) into the external anal sphincter of horses, and how it impacts the anal pressure. The findings document that injections of BTB have similar effects in horses as in other species, but horses might be more sensitive to BTB. The study suggests that injections of BTB could potentially reduce incisional dehiscence after the repair of perineal lacerations in mares.

Methodology

• The study was conducted on 11 healthy adult horses. Both peak and resting anal pressures of the horse were measured using a rectal probe connected to a pressure transducer.
• Anal pressures were documented before the treatment and after the injection of either BTB or a saline solution. Various doses of BTB (500, 1,000, 1,500, and 2,500 U) were used for the study.
• Any physical changes, behavioral alterations, and changes in anal pressure were recorded for each horse.

Results

• With the injection of 1,000 U of BTB, a significant reduction in the peak anal pressure was observed from day 2 to 84, in comparison with the control horses.
• The most pronounced effect of the toxin was noticed within the first 15 days post-injection. This was followed by a gradual return to baseline over a period of 168 days.
• Injecting 2,500 U of BTB resulted in lethargy, generalized weakness, and swallowing difficulties in one horse over a period of 14 days.
• No adverse clinical effects were observed in horses after injections with 500, 1,000, or 1,500 U of BTB.

Conclusion

• The effect of localized BTB intramuscular injection in horses mirrors the effects reported for several other species.
• However, horses appeared more responsive to BTB than other species, and symptoms of botulism might occur at doses exceeding 1,500 U.
• The findings suggest that BTB injections in the external anal sphincter might be beneficial in decreasing incisional dehiscence after the rectification of perineal lacerations in mares.