Directionality of limb and facial asymmetries in non-elite equine populations has been previously reported with results indicating strong similarities to those reported in racehorses. This investigation aimed to consider the relationship between the magnitude of the asymmetries presented within the general equine population, and their previously reported directionality. Direct measurements of 15 bilateral traits (four facial and 11 limb) were captured from a mixed population of 100 horses and ponies. The pooled (whole) population was considered further as horse (withers height >148cm) and pony (withers height ≤148cm) groupings. Each of the three groups were further sub-divided for each trait, into individuals presenting with larger left or larger right sides. Asymmetries were compared as mean asymmetries and as percentages of the trait size at each grouping level. Asymmetry magnitudes were largely reflective of the directional asymmetries previously recorded. Both the horse and pony groups presented with significantly longer right side third metacarpal (P≤0.001) and third metatarsal (P≤0.05 and P≤0.001) bones, whilst in the horse group, the left fore proximal phalanx was both longer and wider compared to the right (P≤0.001 and P≤0.05). This pattern is reflective of the biomechanical preference for left lead anticlockwise) canter, previously only observed in racehorses. The proximal phalanx of the forelimb potentially compensates for the higher loading forces associated with the lead forelimb. When scaled as percentages of trait size, the asymmetry magnitudes largely reflected those reported in humans, suggesting similar criteria could be applied when considering stock selection and controlling for injury predisposition in horses.
- Distal limb