Mechanical nociceptive thresholds in the axial skeleton of horses

An objective measure of neck, back and croup pain is needed in horses with musculoskeletal injuries, vague upper limb lameness or poor performance.

To establish mechanical nociceptive thresholds (MNTs) within the axial skeleton and evaluate the effects of subject status and ridden exercise.

Thirty-six mature horses (10 nonridden; 26 actively ridden) were used to assess MNTs evoked by a pressure algometer (PA) with a 1 cm2 rubber plunger tip at 62 midline and bilaterally symmetrical anatomical landmarks along the axial skeleton. Pressure was applied at a uniform rate of application until a local avoidance reaction was noted. The repeatability of 3 consecutive measurements was evaluated. Left-to-right comparisons and the effects of subject status and ridden exercise on MNTs were assessed.

MNTs were repeatable and increased in a cranial-to-caudal gradient within the axial skeleton. Typically, there were no significant left-to-right differences. Within-horse variability was less than between-horse variability. Higher MNTs were measured in young, heavy, non-Thoroughbred, castrated males, and in horses that were ridden and actively exercised.

PA provides an objective, noninvasive, and repeatable tool to measure mechanical nociception in horses. MNTs vary in horses with differing subject status and ridden exercise level.