Prevalence of objectively measured movement asymmetry in yearling Standardbred trotters

Abstract Background Objective measurement of movement asymmetry is gaining in popularity, especially as an adjunct to traditional lameness evaluation. Earlier research has highlighted the need for more knowledge regarding the clinical significance of measured movement asymmetry, and the influence of biological variation. Evaluating the locomotor system of the Standardbred trotter can be challenging, and studies using objective technology on this breed are few. The aim of this study was to quantify the prevalence and magnitude of objectively measured movement asymmetry in young, presumed sound Standardbred trotters, by performing objective movement analysis during in-hand trot and while driven on a track. Our hypothesis was that asymmetry scores would be higher when evaluating horses in-hand versus while driving on a track.Results Of 103 horses included in the study, 77 were measured both in-hand and on the track, 24 were measured only in-hand, and two were measured only on the track. Previously set symmetry thresholds for the measurement system were used, during both in-hand and track trials. The majority of horses (91, 88.3%) did not have any trials below threshold. Front and/or hind limb parameters were above the symmetry thresholds during in-hand trials for 94 (93.1%) horses, and during track trials for 74 (93.7%) horses. For the total 180 in-hand and track trials, 166 (92.2%) trials were above threshold. Asymmetry magnitude ranged from mild to severe, with the majority of horses showing mild asymmetry. A minority of horses (19.7%) switched side of asymmetry for one or more parameters between in-hand and track trials. Trial standard deviations were overall high, mainly due to horse behavior, and this variability should be considered when interpreting the results. There was no significant effect on asymmetry of measuring horses in-hand versus driven.Conclusions A high proportion of presumed sound Standardbred yearlings showed movement asymmetries above previously determined thresholds. The biological and clinical relevance of the study findings may be aided by examining how this asymmetry evolves over time and with training. This is important in order to ensure the welfare of the Standardbred trotter.