Upper Body Movement Symmetry in Reining Quarter Horses during Trot In-Hand, on the Lunge and during Ridden Exercise

SIMPLE SUMMARY: Veterinary lameness examinations often include assessment of the horse while ridden. Movement symmetry data are commonly used to aid veterinary decision making in lame horses. Reference data are available for horses ridden in ‘English style’, but not specifically for horses ridden in ‘Western style’ with considerable differences in head–neck position, tack and riding style. Upper body movement symmetry was measured in thirty reining Quarter Horses (QHs) during trot in-hand, lunged and ridden by one experienced rider on reining-purpose riding surfaces. Movement was marginally more symmetrical in the ridden horse, with small differences of 1–5 mm. Typical for soft surfaces, movement asymmetry indicated reduced weight support with the limb on the inside of the circle and reduced pushoff with the opposite limb. The small but significant asymmetry differences between in-hand and ridden exercise in QHs ridden in ‘Western style’ necessitate further studies in lame horses. Particular focus should be put on investigating the role of ridden exercise for highlighting differences between specific lameness causes and weight bearing and pushoff forces with the lame limb on the inside or outside of the circle. ABSTRACT: Veterinary lameness examinations often comprise assessing ridden horses. Quantitative movement symmetry measurements can aid evidence-based decision making. While these are available for ‘English’ style riding, they are not for ‘Western’ style riding. This quantitative observational study quantified movement symmetry in reining Quarter Horses (QHs). Movement symmetry of the head, withers and sacrum (differences between minima, maxima and upward amplitudes) were quantified with inertial sensors in N = 30 medium/high level reining QHs during trot in-hand, on the lunge and ridden by one experienced rider (straight-line/circles) on reining-purpose riding surfaces. Mixed linear models for movement symmetry assessed the effects of ridden exercise and movement direction (fixed factors), stride time (covariate) and horse (random factor): single factors and two-way interactions with Bonferroni correction at p < 0.05. Three withers and pelvic parameters showed marginally more symmetrical movement when ridden (p ≤ 0.044; 1–5 mm differences). Three withers, three sacrum and one head parameter were significantly affected by movement direction (all p ≤ 0.026), five showed increased asymmetry on the inside rein, and two, quantifying vertical displacement maximum difference, showed the opposite. Riding QHs in ‘Western’ style showed small movement symmetry differences. Circular exercise confirmed increases in weight bearing asymmetry on the inside rein and in pushoff asymmetry on the outside rein. This should be further investigated for differentiating between different causes of lameness.