Researchers at Hartpury University have been investigating asymmetry in a group of 100 non-elite horses. Dr Peter Green explains their results...
MOST of us are not perfectly symmetrical; one of our ears might be higher than the other, one foot larger and so on. The same is true of horses. We have known for some time that in elite, Flat-racing thoroughbreds, the very best performers tend to be those whose left-right anatomy is most balanced. Even in these, however, there are some traits that tend to be asymmetrical.
Researchers at Hartpury University looked at asymmetry in non-elite horses using 100 riding school and pleasure horses and ponies, none of which had achieved more than novice level in any discipline to see what could be learnt.
The researchers measured 11 limb dimensions, including the length of the cannon and first pastern bones, and four facial features such as ear length and width. These were measured by more than one person and on more than one occasion.
As expected, analysis of these measurements revealed differing degrees of asymmetry across the 100 equines. Some had longer cannon bones or thicker knees on the left or right, for example, or a longer ear or wider nostril on one side of the face.
In all of them, there was a tendency for the right cannon bones to be longer and for the right knees and hocks to be thicker. However, for the measurements of the first pastern bone of the forelimb, it was the other way around – the left-fore pastern tended to be both longer and thicker.
The researchers suggest that this is because most horses and ponies prefer a left lead at canter and gallop, which are not symmetrical gaits, and that the differences discovered reflect the differences in loading of the two forelimbs.
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When horses and ponies were considered separately, there were subtle differences – such as the magnitude of asymmetry being less in ponies for some features such as fore-pastern thickness.
The scientists wonder whether this is because riding school and pleasure ponies are less inbred than their elite horse counterparts.
Further reading: Journal of Equine Veterinary Science 93: asymmetry, 103197
