Distal Forelimb Kinematics During the Extended Trot of Dressage Horses Ridden on Two Different Arena Surfaces

Abstract

Introduction: Suspensory apparatus injuries are common in dressage horses. Studies demonstrate that surface type affects hoof forces and distal limb kinematics of equine athletes. Because synthetic race surfaces have lower stiffness and limb loads than dirt surfaces, it was hypothesized that dressage horses have less fetlock hyperextension on a synthetic surface than a dirt surface. Methods: Two-dimensional, high-speed videos (250 Hz, 2 ppcm) of 6 dressage horses (ages 8–13; 5 males, 1 female) during extended trot on dirt and synthetic surfaces (6 trials (strides) per horse per surface) were digitized (low-pass Butterworth filter, 15 Hz). Fetlock and solar hoof angles determined from skin and hoof markers were compared between surfaces using a mixed model ANCOVA that accounted for horse velocity (saddle billet marker) and repeated horse measures. Surface mechanical behaviors were characterized using a track testing device. Maximum force, time to maximum force, maximum displacement, resting rebound, maximum vertical rebound, average stiffness, and maximum load rate were compared between surfaces and time of day (morning, afternoon) using a general linear model ANOVA. Results: Maximum and toe off fetlock angles were greater on the synthetic surface compared to dirt (Δ = 2°, P = 0.070). Mean maximum fetlock angle on the synthetic surface was 260°. The maximum load rate of the synthetic surface was 5 times greater than the dirt surface (P = 0.0086). Conclusions: Synthetic surfaces were designed to reduce injuries in equine athletes. Because suspensory apparatus elongation is largely dependent on fetlock extension, it is possible that suspensory apparatus strain is greater on synthetic surfaces. Thus, surface design may require more refinement to promote injury prevention based on horse discipline and gait. Ethical Animal Research: The University of California, Davis Institutional Animal Care and Use Committee reviewed and approved the protocols used in the study. Owner informed consent was obtained for all study horses. Sources of funding: Merial (A Sanofi Company) in association with the Student Training in Advanced Research (STAR) program, School of Veterinary Medicine, University of California, Davis and the Endowed Research Funds of School of Veterinary Medicine, University of California, Davis. Competing interests: none.