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

To investigate associations between contralateral (left-right) hoof width asymmetry and vertical movement asymmetry in racing Thoroughbreds. We hypothesized that forehoof differences would be associated with poll and withers movement asymmetry and hind hoof differences with pelvis movement asymmetry.

This observational cross-sectional study included 169 Thoroughbred racehorses recently retired from clockwise racing and assessed the day of scheduled farriery work. Contralateral hoof width differences were quantified and movement asymmetry during trot measured using inertial sensors placed on the poll, withers, and pelvis. A primary outcome was the difference in upward movement amplitude between the left and right stance phases (upDiff). Based on measured contralateral hoof width differences, horses were categorized post hoc by the side of the wider hoof, and between-group differences in movement asymmetry were quantified using effect sizes (Cohen d).

70% of horses had wider right forehooves and 65% wider right hind hooves. Forehoof width asymmetry was associated with differences in upDiff at the poll (Cohen d = 0.82) and withers (Cohen d = 0.73), with greater vertical displacement during stance of wider hoof. Hind hoof width asymmetry was not associated with pelvic upDiff but at the poll (Cohen d = 0.57) and withers (Cohen d = 0.60).

Forelimb hoof width asymmetry was associated with poll and withers movement asymmetry, whereas hind hoof width asymmetry was not associated with pelvic movement asymmetry.

Assessment of forehoof width asymmetry may aid interpretation of head and withers movement asymmetry during lameness evaluation and inform hoof care and training management in racehorses.