Morphological and behavioural predictors of motor laterality in domestic horses: A cross-sectional field study.

Motor laterality in horses affects performance, training, and welfare. A simple morphological marker for laterality would help riders, trainers, and veterinarians identify likely locomotor asymmetries early. This study tested whether observable morphological and behavioural characteristics were associated with rider-perceived motor laterality in domestic horses, using a cross-sectional observational field study design conducted in the Blida and Algiers regions of Algeria. The study included 100 regularly ridden domestic horses. Mane orientation, facial whorl characteristics, standing curvature, masticatory laterality, mouth hardness side, spontaneous body bending, and preferred limb use were recorded. Experienced riders assessed two laterality outcomes: preferred forelimb at walk departure (dep1) and ease of canter departure (dep2). Univariable and multivariable analyses tested associations between recorded characteristics and laterality outcomes. Mane orientation was the strongest predictor of laterality (p < 0.001): right-maned horses were predominantly right-lateralised (dep1: 91.1%; dep2: 78.7%), and left-maned horses were mainly left-lateralised (dep1: 89.1%; dep2: 81.1%). In multivariable analysis, mane orientation was the sole independent predictor (dep1 OR = 83.71; dep2 OR = 15.91; GEE OR = 32.12, 95% CI 13.30-77.61). Model discrimination was excellent (AUC = 0.91). Masticatory laterality and mouth hardness side showed significant univariable associations but were not independent predictors. Facial whorl traits, age, breed, discipline, and sex showed no significant associations. The cross-sectional design prevents causal inference. Laterality outcomes relied on rider perception rather than objective kinematic measurements, which introduces possible observer bias. Longitudinal and biomechanical validation remains needed. Mane orientation is a robust, non-invasive indicator of inherent motor laterality in domestic horses and can be used by riders, trainers, and veterinarians to anticipate locomotor asymmetries without specialised equipment. Longitudinal and kinematic studies are required to confirm causality.