Functional locomotor consequences of uneven forefeet for the trot of individual riding horses

Abstract

Reasons for performing study: It has been generally accepted that a symmetrical distal limb conformation is an important prerequisite for a successful performance, as it has often been hypothesized that uneven feet should be considered as an important enhancing factor for the development of lameness. On a population level it has been demonstrated already that uneven footed horses seemingly are retired earlier from competition, but the biomechanical consequences for an individual horse are not known yet.

Objectives: To provide a better definition of uneven feet using objective quantifiable variables, to evaluate the functional (a)symmetries of horses with even and uneven feet, and to evaluate the functional differences between feet categorized as flat, medium or upright.

Methods: Eight anatomical parameters that quantified conformational differences in the distal forelimbs of horses with a varied range of hoof asymmetries (n=36, of which 2 were lame at trot) were compared using discriminant analysis. Kinetics and distal limb kinematics of the clinically non-lame horses were collected at trot and compared between even versus uneven forefeet and between flat, medium and upright feet using MANOVA followed by ANOVA. The relative influence of differences in hoof angle between the forefeet and of absolute hoof angle on functional parameters was analyzed by multiple regression analysis.

Results: It appeared that unevenness was best determined by the absolute differences in dorsal hoof angle between the forefeet. In horses with uneven feet, the flatter foot showed a significantly larger maximal horizontal braking and vertical ground reaction force, a larger vertical fetlock displacement and a less stiff limb spring. A steeper hoof angle was linearly correlated with an earlier braking-propulsion transition. No significant differences were found between feet categorized as flat, medium or upright.

Conclusion and potential relevance: The conformational differences between the forefeet were more important for loading characteristics than the individual foot conformation. The recorded differences in vertical force between the uneven forefeet could in fact imply an early, subclinical sign of lameness developing in the steeper forefoot, as these kinetic differences yet appeared even smaller than those reported for a subtle lameness when becoming clinically evident.