Hoof and movement asymmetry in Thoroughbred racehorses with predominantly single direction training.

Forehoof width asymmetry significantly confounds head and withers movement asymmetry, warranting assessment during racehorse lameness evaluations.

This observational cross-sectional study investigated the relationship between contralateral hoof width asymmetry and vertical movement asymmetry in 169 Thoroughbred racehorses recently retired from clockwise (single-direction) racing. Hoof width differences were quantified bilaterally for both fore and hind hooves, and movement asymmetry during trot was measured using inertial sensors placed at the poll, withers, and pelvis. The primary outcome measure was the difference in upward movement amplitude between left and right stance phases (upDiff). Results demonstrated that 70% of horses had wider right forehooves and 65% had wider right hind hooves, consistent with the directional bias of clockwise training. Forehoof width asymmetry showed meaningful associations with poll (Cohen d = 0.82) and withers (Cohen d = 0.73) movement asymmetry, with greater vertical displacement occurring during the stance phase of the wider hoof. Notably, hind hoof width asymmetry was not associated with pelvic movement asymmetry but did show moderate associations with poll (Cohen d = 0.57) and withers (Cohen d = 0.60) movement. These findings suggest that forehoof morphological asymmetry is a significant confounding factor in standard lameness evaluations that rely on head and withers movement patterns. Clinicians should consider hoof width asymmetry when interpreting inertial sensor-based lameness data, as structural hoof differences may produce movement asymmetries that mimic or mask true lameness. This work also highlights the importance of targeted hoof care and training management strategies to mitigate asymmetry development in racehorses undergoing predominantly single-direction exercise.

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