Effect of Weighted Boots Used with Different Shoeing Styles on Limb Movement and Ground Reaction Forces in Icelandic Horses at Walk, Tölt and Trot

Introduction Weighted boots and unnaturally high and long hooves (SH) are used to improve the 4-beat rhythm of the tolt and enhance forelimb action. Methods The effect of these methods on loading and movement of the limbs was investigated in thirteen Icelandic horses at walk, tolt and trot on an instrumented treadmill. Vertical ground reaction forces and kinematic data of fore- and hindlimbs were measured. Four conditions were differentiated: SN (standard shoeing) and SH, without and with weighted boots of 240 g (WB240), respectively. Differences were tested using one-way repeated measures ANOVA, separately for each gait (P<0.05). Results At the tolt, in both shoeing styles, WB240 increased protraction height of the forelimbs by about 13%. The weight gain of 273 g at the distal limb induced by changing SN to SH had a similar and cumulative effect. Hoof length alone was also positively, but not significantly, associated with protraction height; the combination of SH and WB240 resulted in an increase of up to 35%. Lateral coupling (pace-like rhythm) in tolt was reduced only with a combination of SH and WB240. Stride impulse increased with a change of hoof conformation alone at tolt, and combined with weight at all three gaits. Shorter relative stance durations in the forelimbs particularly at faster speeds resulted only in a minor increase of peak forces (+1.4%) due to an impulse shift to the hindlimbs. Conclusions Weight, particularly in combination with SH, improved gait performance and marginally increased limb peak forces. However, enhanced inertial forces during swing might additionally stress internal distal limb structures. Ethical Animal Research The experiment was carried out with the approval of the Animal Health and Welfare Commission of the Canton of Zurich (No. 206/2010). Owner written informed consent was obtained. Sources of funding: Stiftung Forschung fur das Pferd, the Haldimann Stiftung, the Swiss Metall Union, the Stiftung Temperatio, the Swiss Veterinary Office (FVO) and the Islandpferde-Vereinigung Schweiz. Competing interests: none.