Investigation into thoracic asymmetry in ridden horses

Abstract

Progressive training of horses focusses on the muscular development and flexibility to both the right and the left. However anecdotal evidence suggests that horses are not symmetrically structured through the thoracic region and this may have effects on saddle fitting and performance. The aim of this research was to determine if asymmetry exists in the thoracic musculoskeletal structure of ridden horses by analysing retrospective data of saddle fits (n=490) obtained from a saddle fitting company. A flexible wither tracer tool was used to obtain tracings of wither shape. Each tracing yielded four repeatable points (two on the left; two on the right) measured from the midline at the highest and lowest points of the withers. Descriptive assessments of shoulder, wither, and back shape, and demographic information on both horse and rider were recorded. A Wilcoxon signed-rank test compared the means of the wither shape measurements. A GLIMMIX procedure identified relationships between the wither measurements, descriptive assessments, and horse and rider demographics. The means of measurements from the wither tracer tool showed almost 60% of horses having larger measurements on the left side (P<0.0001). There was no effect of horse breed, age, sex, height or level of training on wither measurements (P>0.05). Rider age, gender, height, weight and level of training did not affect wither measurements (P>0.05). These results show that horses are asymmetric in their thoracic structure with a majority of horses larger on their left side than the right. This asymmetry may be due to genetics, environment or training and should be considered when fitting a saddle to the horse.