Mechanical nociceptive thresholds within the pastern region of Tennessee Walking Horses

Summary Reasons for performing study: ‘Soring’ is the term used to describe the application of an irritant to the distal forelimbs of gaited horses with the sole intent of inflicting pain and inducing altered gait, illegally practiced in Tennessee Walking Horses. Objective methods for the detection of limb pain due to this practice are, however, lacking. Objectives: To assess whether Tennessee Walking Horses respond to manual pressures ≤10 kg/cm2 and to establish reference mechanical nociceptive thresholds (MNTs) within the pastern region. Methods: In 25 mature Tennessee Walking Horses in which no irritant had been applied, MNTs were evoked by a pressure algometer at 4 sites within the pastern region of each thoracic limb by 6 different examiners. The effects of age, sex, weight, height at withers, exercise and hand dominance of the examiners on MNTs were assessed. Correlations between the horse's perceived mental status, tolerance to the procedure and MNT values were also evaluated. Results: Mechanical nociceptive thresholds ≤10 kg/cm2 were observed in 20% of measurements, of which the mean ± s.d. MNT was 9.5 ± 0.3 kg/cm2. Within 4 pastern sites, the palmar region had the lowest reference MNT value of 19.5 ± 3.6 kg/cm2. Subject status, exercise, hand dominance, horse mental status and horse procedure tolerance did not significantly affect MNT values. Conclusions: Reference MNTs of the pastern region of nontreated Tennessee Walking Horses provide an objective standard for the evaluation of those potentially applied irritant. Potential relevance: Pressure algometry, in lieu of digital pressure, can quantify mechanical pressure applied during inspections to detect irritant therapy and provide consistency between examiners.