Does long-term unilateral circling affect locomotor symmetry in ponies used for carousel rides?

There is ethical debate on the use of ponies for carousel rides at city fairs, as these animals may develop progressive locomotor asymmetry during their career. To investigate this issue, 21 ponies used for carousel rides were walked and trotted over a pressure plate system. Non-directional symmetry ratios and directional asymmetry indices of forelimb peak vertical force (PVF), vertical impulse (VI), stance time (ST) and hoof contact area (CA) were calculated and compared to reference data. In both the carousel and reference groups, most ponies presented higher loading of the right forelimb at the walk and trot. Carousel ponies presented slightly, though significantly, lower symmetry ratios and more negative asymmetry indices than the reference group for PVF and VI, but not for ST and CA. However, repeated analysis after exclusion of the ponies with visually observed lameness revealed no significant differences in asymmetry indices, whereas symmetry ratios remained lower in the carousel group. Interestingly, Ten of 21 carousel ponies were subjectively more difficult to lunge on the circle opposite to their routine working direction, whereas the ponies in the reference group were easily lunged in both directions. In the absence of clear unilateral lameness or locomotor asymmetry in the majority of ponies, it is reasonable to assume a behavioural explanation for this observation. There was no significant association between the duration of the career and all symmetry indices. These results indicate an overall less symmetric locomotion in carousel ponies, but progressive locomotor asymmetry due to long-term unilateral circling seems to be unlikely.