Most horses “lefties”, saddle fit and wither symmetry review finds

Years of measurement data from 490 horses was gathered from a saddle fitting company, which used a flexible wither tracing tool.
Image by Th G

A retrospective study looking at wither symmetry and its relationship to saddle fitting has found that a majority of horses are “lefties”, with 60% having larger measurements on their left side.

The research team from the University of Guelph digitized and compared years of measurement data from 490 horses gathered from a saddle fitting company, which used a flexible wither tracing tool.

Dr Katrina Merkies, researcher and associate professor at the University of Guelph, said the results were not surprising. The empirical evidence backed up the hypothesis expecting more bulk on the left, based on what saddle fitters were already noticing in their day to day work, she said.

But what does this mean for the horse owner shopping for a new saddle, manufactured in a perfectly symmetrical way?

Pressure points from an ill-fitting saddle can lead to pain and performance issues. A symmetrical saddle used on a horse that is not symmetrical can hinder progress, making balanced muscle development difficult, Merkies said.

The research study included many breeds, from fine boned Arabs and Thoroughbreds to stocky Warmbloods and Drafts. They came from many disciplines such as dressage, hunter/jumper as well as recreational pursuits. Surprisingly, breed did not have an effect on wither measurements in this study. While Thoroughbreds and Warmbloods had different skeletal structure, such as longer withers than the Draft breeds, it did not have an impact on the wither measurements which were based on the horse’s musculature.

Laterality — the preference for using one side of the body over the other — was also considered for its possible role in muscle development. The left hemisphere of the brain (logic and reasoning) controls the right side of body, and the right side of the brain (processes fearful stimuli) controls the left side.

“You may notice horses often turn to view an object they are afraid of with their left eye,” Merkies said. “They often step on or off a trailer with the left front leg first.”

Merkies also mentioned an Australian study noting a preference for grazing with the left front leg ahead of the right; a tendency that apparently increases with age.

One unexpected finding was the curvature in the horse’s backs were slightly more dipped in horses of medium height. Merkies hypothesised this may be because medium sized horses are more frequently ridden by adults. Kids tend to move off their ponies as they outgrow them. Saddles for the adult rider tend to have a longer seat, which may not always fit the medium sized horse’s back. If the saddle fits past the 18th thoracic vertebrae, it will put pressure on the lumbar region, which can cause a horse to tense and drop its back muscles.

Merkies cited the need for controlled studies looking at asymmetry and saddle fit following properly fitted asymmetrical horses over time.

The research was carried out by Guelph undergraduate students Julia Alebrand, Bethany Harwood, Katharine LaBarge and Laura Scott.

Investigation into thoracic asymmetry in ridden horses. Merkies, K.; Alebrand, J.; Harwood, B.; LaBarge, K.; Scott, L. Comparative Exercise Physiology, Volume 16, Number 1, 5 February 2020, pp. 55-62(8).

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