Mechanical nociceptive thresholds in endurance horses.

The researchers designed a method to measure how much force it takes to cause discomfort or pain in endurance horses’ forelimbs, also known as the mechanical nociceptive threshold. They found this method viable, safe, and well-received by the horses, it could distinguish between horses with typical sensitivity and those with impaired sensitivity.

Objective and Methodology

• The study aimed at developing an objective method useful in the field to determine the mechanical nociceptive threshold (MNT) or measure of pain in endurance horses. The team used a remotely controlled pneumatic actuator with a 1 mm tip to measure this threshold on the forelimb pastern of 108 endurance horses.

Key Findings

• The median MNT at rest was 1.9 N (Newton – unit of force) with a range between 0.9 and 3.5 N. This indicates that when at rest, it took a median force of 1.9N to cause discomfort or pain to the horses.
• The study found that icing had no significant effect on limb sensitivity, which contradicts a common belief that ice can lessen sensitivity.
• MNT measured weekly increased from week 1 to week 3, showing an increase in the horse’s tolerance to force over time.
• In 17 horses which were observed to not have impaired sensitivity, the MNT increased after a race.
• In comparison, horses found to have unnaturally low sensitivity, MNT following a race was considerably higher. The researchers can infer that these horses had been artificially desensitised.
• Desensitisation with a drug called mepivacaine increased MNT to above the safety cut-off at 10 minutes. However, the sensitivity returned to baseline varied between individuals but recovered by 330 minutes.
• None of the horses became averse to the technique, indicating it was well-tolerated.

Conclusion

• The researchers found the technique for measuring MNT to be practical, non-traumatic, repeatable, and well-tolerated under field conditions with endurance horses.
• Moreover, it was effective at differentiating between horses with normal sensitivity and those with impaired sensitivity, which could be beneficial for enforcing rules against altering limb sensitivity in equine sports.