Lateralised motor behaviour leads to increased unevenness in front feet and asymmetry in athletic performance in young mature Warmblood horses.

REASON FOR PERFORMING STUDY Foot stance in grazing significantly influences hoof conformation and development from foal to yearling age. OBJECTIVES To conduct a longitudinal study to establish if the relationship between motor laterality and uneven front feet persisted in 3-year-old horses at the time of studbook selection and to investigate if such laterality and unevenness might influence the horses' ability to perform symmetrically while trotting, cantering and free jumping. METHODS Seventeen clinically sound but untrained (with only minimal experience of handling) and sound Warmblood horses that had participated in a previous study were assessed as per the protocol reported. Laterality was tested in a preference test (PT) and z-values were calculated for analysis purposes. Laterality and hoof unevenness were related to both relative limb length and relative head size, while the ability to perform symmetrically was tested in free trot-canter transitions and free jumping exercises. Differences in performance between horses with and without a limb preference in the PT and those with 'uneven' and 'even' feet were tested for differences in performance metrics using Students' t test, while linearity was tested using a regression analysis (P<0.05). RESULTS Significant laterality was still present in 24% of the 3-year-old horses and the relationship between laterality and uneven feet pairs was stronger than at foal and yearling stages. Horses with significant motor laterality had almost 4 times more unevenness, a smaller head and longer limbs and the relationship between body conformation and laterality was still present. There was a strong linear relation between unevenness, laterality and a bias or side preference for trot-canter transitions. However, this relationship was not significant during the free jumping exercise. CONCLUSION Motor laterality and uneven feet pairs were still present and significantly related in the 3-year-old horses and both variables were also strongly related to sidedness in trot-canter transitions. POTENTIAL RELEVANCE Warmblood studbooks should include quantitative data on laterality at the time of studbook admission as part of the selection criteria.