Mechanical nociceptive thresholds in endurance horses

Abstract

BackgroundAlteration of limb sensitivity is forbidden in equine sports but difficult to enforce. We aimed to develop an objective field method to assess mechanical nociceptive threshold (MNT) in endurance horses.MethodsA remotely controlled pneumatic actuator (1 mm tip) was used to measure forelimb pastern MNT in 108 endurance horses.ResultsMedian (IQR) MNT at rest was 1.9 N (0.9–3.5). Icing had no significant effect on limb sensitivity. MNT measured at weekly intervals increased from week 1 (1.2 N (0.6–1.8)) to week 3 (1.9 N (1.2–2.8)) (P<0.05). In 17 horses without impaired sensitivity, MNT increased from 1.2 N (0.6–2.3) before to 2.4 N (1.2–5.2) after racing (P=0.0017). In desensitised horses, MNT after racing was higher (8 limbs—23.1 N (21.4 to >25)) than in horses without impaired sensitivity (42 limbs—2.2 N (1.2–4.3)) (P<0.0001). Desensitisation with mepivacaine increased MNT to above the safety cut-off (25 N) at 10 minutes; sensitivity return to baseline varied between individuals but was restored by 330 minutes. None of the horses became averse to the technique.ConclusionMNT was practical, non-traumatic, repeatable and well tolerated under field conditions in endurance horses. The technique differentiated postracing MNT in horses with normal sensitivity from those with impaired sensitivity.

Remote Controlled Nociceptive Threshold Testing Systems in Large Animals

“…In horses, neither TT nor MT changed significantly over several weeks [27,[37][38][39]. Pastern MT remained stable or even increased with familiarity over a few weeks, even when attached to the operator by a long light pressure line [26]. The ability of remote control to avoid visual cues and allow normal behavior presumably contributes to this.…”

“…The mechanical system, however, required generation of air pressure to drive the actuator pin, necessitating attachment of a gas reservoir and metered pressure control being fitted to the animal. Wired or handheld MT testing systems driving a pneumatic actuator can make use of manual compression of a syringe [21,22,26]. Both air reservoir (the syringe) and pressure control (e.g., following visual pressure indicators) are under operator control and not fixed to the animal.…”

Remote Controlled Nociceptive Threshold Testing Systems in Large Animals

“…The mechanical system, however, required generation of air pressure to drive the actuator pin, necessitating attachment of a gas reservoir and metered pressure control being fitted to the animal. Wired or handheld MT testing systems driving a pneumatic actuator can make use of manual compression of a syringe [21,22,26]. Both air reservoir (the syringe) and pressure control (e.g.…”

“…In horses neither TT nor MT changed significantly over several weeks [27,[37][38][39]. Pastern MT remained stable or even increased with familiarity over a few weeks even when attached to the operator by a long light pressure line [26]. The ability of remote control to avoid visual cues and behave normally presumably contribute to this.…”

Pressure Algometry for the Detection of Mechanical Nociceptive Thresholds in Horses

“…Epidural morphine [32] Epidural ropivacaine [33] Low-4-point block [34] Digital flexor tendon sheath [35] Distal interphalangeal joint [22] Palmar digital nerves [36] Response to therapy Chiropractic [37] Chiropractic, low-level laser therapy [38] Chiropractic, massage, phenylbutazone [39] Static magnetic blanket [40] Pulsed electromagnetic therapy blanket [41] Extracorporeal shockwave therapy [42] Tail traction [21] Sublingual detomidine [43]…”