Asymmetries of horses walking and trotting on treadmill with and without rider

BACKGROUND: Left-right movement symmetry is a highly desirable characteristic in sport horses.OBJECTIVES: This study compared movement symmetry in well-trained dressage horses unridden and unrestrained, and ridden in a dressage frame, and investigated possible associations between gaits.STUDY DESIGN: Experimental study.METHODS: Seven sound, high-level dressage horses were measured in walk and sitting trot on a treadmill at several speeds under two conditions: with and without rider. Left-right differences for stance duration, stance protraction and retraction based on longitudinal hoof positions, ipsilateral limb tracking, minimum and maximum vertical positions of the dorsal spinous processes of the sixth thoracic (T6), third sacral vertebrae (S3) and wing of atlas, and vertical ground reaction forces were calculated and analysed in mixed models.RESULTS: In walk, five body variables indicated increased asymmetry when ridden compared to unridden: forelimb stance duration (unridden/ridden left-right differences 9 vs. 13 ms; P=0.008), forelimb stance protraction (P=0.004), stance retraction (P=0.001) and first force peak (P=0.003), and hindlimb stance retraction (P=0.01). In trot, six body variables were more asymmetrical when ridden: forelimb stance duration (2.5 vs 3.8 ms, P=0.004); hindlimb stance protraction (P<0.0001) and retraction (P=0.01), T6 minimum (4 vs 6 mm, P=0.001), T6 maximum (9 vs 11 mm, P=0.01) and S3 maximum (6 vs 12 mm, P<0.001). Five variables had significant associations between asymmetries in walk and trot, but only three demonstrated a positive slope.MAIN LIMITATIONS: A limited number of horses and riders were studied. Measurements were performed on treadmill.CONCLUSIONS: High-level horses moved slightly more asymmetrically when ridden in a dressage frame than when unridden.