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

Overview

• This study examined the relationship between differences in hoof width on the left and right sides and asymmetrical movement in retired Thoroughbred racehorses trained predominantly in one direction.
• The research aimed to understand how hoof width asymmetry correlates with vertical movement asymmetry in different parts of the horse’s body during trot, particularly focusing on the forehooves and hind hooves.

Study Purpose and Hypotheses

• The researchers wanted to investigate if differences in hoof width between the left and right hooves of forelimbs and hind limbs are associated with vertical movement asymmetry.
• They hypothesized two main associations:
  • Forehoof width differences would correlate with movement asymmetry at the poll (top of the head) and withers (top of the shoulders).
  • Hind hoof width differences would relate to movement asymmetry at the pelvis.

Methods

• The study was observational and cross-sectional, involving 169 Thoroughbred racehorses that had recently retired from clockwise racetrack training.
• Measurements were taken on the day of scheduled farriery (hoof care) work.
• Key data collected:
  • Contralateral hoof width differences (left vs. right hooves) were measured.
  • Vertical movement asymmetry was measured during trot using inertial sensors placed on three body locations: poll, withers, and pelvis.
  • The primary outcome metric was the difference in upward movement amplitude during the left versus right stance phases, called “upDiff”.
• Horses were grouped post hoc based on which side had the wider hoof, and movement asymmetry was compared between groups using Cohen’s d effect size.

Results

• A majority of horses showed right-sided hoof width asymmetry:
  • 70% had wider right forehooves.
  • 65% had wider right hind hooves.
• Forehoof width asymmetry showed a strong association with vertical movement asymmetry at the poll and withers:
  • Cohen d = 0.82 at the poll.
  • Cohen d = 0.73 at the withers.
  • Movement amplitude was higher on the side of the wider forehoof.
• Hind hoof width asymmetry did not significantly relate to pelvis movement asymmetry (expected association).
  • However, hind hoof asymmetry was linked to some asymmetry at the poll and withers (Cohen d of 0.57 and 0.60 respectively), unexpected findings.

Conclusions and Implications

• The study confirmed the hypothesis that forelimb hoof width differences associate with head and shoulder movement asymmetry during trot.
• Contrary to expectations, hind hoof width differences were not linked to pelvic movement asymmetry but did relate to upper body movement asymmetry.
• These findings suggest:
  • Forehoof width asymmetry is an important factor to consider when interpreting movement asymmetry during lameness evaluations.
  • Knowledge of hoof width differences can assist farriers and trainers in managing hoof care and training regimens, potentially improving horse performance and welfare.