The Hoof Inside Out: A Comprehensive Investigation About the Shoe Configuration Effects on the Behavior of the Equine Hoof
Authors:   , Aoun Rita 
Published: July 2024

"The equine hoof is a unique organ in biology that has intricate elastic properties. From simple protection to therapeutic and corrective measures, horseshoes are widely used in the equine industry. Various types of shoeing have been designed and used based on their unique targeted functions following hoof care. Shoes can modify the gait of the horse, affect the alignment of the distal joints, and alter stress and strains on specific hoof regions. The objective of this dissertation is to provide an overview of the available research on the existing methodology and literature on the effects of shoeing on equine gait and study the effects of specific widely used shoes in vitro and in vivo. The first study qualitatively evaluated the existing literature and characterized the known methodologies, findings, and limitations when investigating shoe configurations. Although shoes can be beneficial as shown in many sources, however findings can be specific/subjective with the risk of bias when it comes to generalization of the results. That is related to the potential methodological and analytical errors that researchers may introduce like unfit statistical study design, non-repeatable mode of collection and/or analysis or data, lack of comparison to a control when testing a modification on a shoe. Altogether, existing data may still be anecdotal and future work in the field needs care to be able to make immediate conclusive inferences. The second study focused on investigating three of the widely used open-heel, egg-bar, and heart-bar shoes on in vitro model of the stance of a live horse comparing unaffected to laminitic specimens, under a mechanical testing with a continuous axial load up to a maximum of 5.5x103 N (similar to the weight of an average horse). Results showed that there was a clear difference in behavior between clinically normal and laminitic hooves. The findings indicated that out of three tested shoes, only egg-bar and heart-bar configurations were successful in decreasing abnormal third phalanx (P3) motion. Specifically, heart-bar shoes lowered P3 sinking in unaffected and laminitic hooves and lowered P3 rotation from the dorsal wall compared to unshod in laminitic hooves. In addition, shoes generally reduced hoof quarter expansion. This led to the third study that focused on investigating wooden clog shoes, famously known in the laminitis industry, on the motion and radiographic measurements of unaffected versus laminitic specimens. This exclusive in-vitro model applied step loads at increments of 25% of the maximum (5.5x103 N) on unaffected and laminitic digits in a mechanical testing system. The study results showed that the wooden clog shoe differently affected heels length and heel widths than other shoes, and significantly lowered abnormal P3 vertical sinking, specifically in laminitic specimens. The iron-based shoes did not show promising effects on laminitic hooves. Finally, the 2-D radiographic measurements were not statistically correlated to the 3-D surface motion measurements. The fourth study investigated the effect of the shoes, tested in the third study, on the kinetics of walking horses over force sensing platform. Although the overarching goal may be to test the shoes in vivo, an examination in laminitic horses was not humanely possible. The study results were promising and showed distinctive changes in gait kinetics were detected with the wooden clog shoe, supporting their use to reduce vertical forces on forelimbs at full support. Differences between the wooden clog and the other iron-based shoes were clear and predictable, using a machine learning model, specifically when investigating its effects on the time to peak forces and time of braking to propulsion phases. Additionally, it was found that egg-bar and open-heel shoes focus the sagittal resultant force vectors more vertically than other shoes or when unshod. The results enhance knowledge of shoe effects on equine kinematics and highlight cutting-edge tools to quantify them. The results of this work emphasize the potential benefits of the wooden clog in decreasing painful abnormal displacement of P3 in vitro and reducing high forces and allowing for a shorter and smoother breakover in vivo. Taken together, the findings of this work accentuate the importance of the effects of shoeing and shoe configurations on P3 displacement and hoof deformation during load application. The findings of the in-vitro model and the in-vivo testing of shoeing are critical for veterinarians and farriers, as to guide shoe selection and future designs for optimum hoof protection and performance."