Shoe configuration effects on equine forelimb gait kinetics at a walk

The shift in vertical forces on the equine hoof surface by heart-bar, egg-bar, and wooden clog shoes can significantly impact gait kinetics. Hypotheses tested in this study were that vertical, braking, and propulsion peak force (PF) and impulse (IMP) are different while shod with heart-bar, egg-bar, open-heel, and wooden clog shoes, or while unshod, and the resultant ground reaction force vector (GRF ) has the longest duration of cranial angulation with open-heel shoes followed by unshod, then egg-bar and heart-bar shoes, and the shortest with wooden clog shoes. Forelimb GRFs were recorded as six non-lame, light-breed horses walked across a force platform (four trials/side) while unshod or with egg-bar, heart-bar, open-heel, or wooden clog shoes. Outcomes included vertical, braking, and propulsive peak forces (PF_V, PF_B, PF_P) and impulses (IMP_V, IMP_B, IMP_P), percent stance time to each PF, braking to vertical PF ratio (PF_B/PF_V), walking speed (m s^-1), total stance time (ST) and percent of stance in braking and propulsion. The magnitude and direction of the resultant GRF vectors were quantified at 5% stance increments. Kinetic measures were compared among shoeing conditions with a mixed effects model (p-value < 0.05). A random forest classifier algorithm was used to predict shoeing condition from kinetic outcome measures. All results are reported as mean ± SEM. Trial speed, 1.51 ± 0.02 m s^-1, was not different among shoeing conditions. The PF_V was lower with wooden clog (6.13 ± 0.1 N kg^-1) versus egg-bar (6.35 ± 0.1 N kg^-1) shoes or unshod (6.32 ± 0.1 N kg^-1); the PF_P was higher with wooden clog (0.81 ± 0.03 N kg^-1) versus open-heel (0.71 ± 0.03 N kg^-1) or egg-bar (0.75 ± 0.03 N kg^-1) shoes or unshod (0.74 ± 0.03 N kg^-1), and lower with open-heel compared to heart-bar shoes (0.77 ± 0.03 N kg^-1). Both IMP _B and IMP_V were higher with open-heel shoes (-0.19 ± 0.008 N s kg^-1, 3.28 ± 0.09 N s kg^-1) versus unshod (-0.17 ± 0.008 N s kg^-1, 3.16 ± 0.09 N s kg^-1), and IMP_V was higher with wooden clog shoes (3.26 ± 0.09 N s kg^-1) versus unshod. With wooden clog shoes, PF_B/PF_V (0.12 ± 0.004) was higher than unshod (0.11 ± 0.004). Percent time to peak PF_V, PF_B, and PF_P, and percent braking time were highest and percent propulsion time lowest with wooden clog shoes. The magnitude of the GRF vector with the wooden clog shoe was the highest among shoeing conditions during the first stance half, lowest during the second stance half, highest during late propulsion, and had the most gradual braking to propulsion transition. Vectors were angled cranially with wooden clog shoes slightly longer than the others. Wooden clog shoes was the only shoeing condition accurately predicted from kinetic measures. Distinct, predictable changes in gait kinetics with wooden clog shoes may reduce stresses on hoof structures. Study results enhance knowledge about shoe effects on equine gait kinetics and cutting-edge measures to quantify them.