The relationship between hoof conformation and racing history in thoroughbred horses using computed tomography

Introduction.

International Thoroughbred racehorses traveling to Australia to compete have a higher incidence of musculoskeletal injuries (MSI) when compared to horses that compete in Australia only (local horses). The fetlock is the most commonly affected joint in these horses and previously we have shown that hoof conformation was associated with loads generated in the fetlock joint during locomotion and with scintigraphic evidence of fetlock bone injury (1, 2). To investigate whether hoof conformation contributes to this higher incidence of MSI in international horses, we measured the hoof angles of local and international racehorses. We hypothesized that international horses have lower dorsal hoof wall angle (DHWA), palmar angle (PA) and hoof pastern angle (HPA) compared to local horses.

Materials and Methods.

The distal forelimbs and hindlimbs of 84 Thoroughbred racehorses that were competing without evidence of lameness were scanned standing, under sedation with a dedicated equine fan-beam CT system (Asto Equina® CT). All measurements were made using the angle tool in dicom viewer software (RadiAnt®). Analysis was performed using multivariable general linear models to enable adjustment for horse factors such as age, bodyweight and racing history.

Results.

The DHWA of international horses was lower than that of local horses (46.6±2.3° vs. 49.4±1.9°, P<0.001), for PA there was no difference between local and international horses (P=0.083), and for HPA international horses had a lower angle than local horses (163.4±4.9° vs. 166.0±4.9°, P=0.004).

Discussion/Conclusion.

Hoof conformation differed between local and international racehorses. Further investigations should explore whether hoof conformation contributes to the higher incidence of MSI in international horses competing in Australia, and whether these conformation differences result from differences in local and international racetrack surfaces.

References

1. Harrison SM, Whitton RC, Kawcak CE, Stover SM, Pandy MG. Evaluation of a subject-specific finite-element model of the equine metacarpophalangeal joint under physiological load. Journal of Biomechanics. 2014;47(1):65-73.
2. Walmsley EA, Jackson M, Wells-Smith L, Whitton RC. Solar angle of the distal phalanx is associated with scintigraphic evidence of subchondral bone injury in the palmar/plantar aspect of the third metacarpal/tarsal condyles in Thoroughbred racehorses. Equine Vet J. 2019;51(6):720-6