horse joints
Science is bringing a new angle to equine morphology evaluations.

Recent study results highlight the importance of specific angles in a horse’s conformation that can affect not only his looks but also his performance, health, and welfare.

“We need to be viewing these angles, in part, as insight into a horse’s physical limitations and respect those, because they’re just part of his genetics and can’t be modified through training,” said Annik Gmel, PhD, of the Agroscrope national agricultural research center and Swiss National Stud, in Avenches, Switzerland.

Gmel and her fellow researchers identified two conformation angles that link to a specific gene, affecting the size of the angle. One was the natural angle of the head and neck (at the poll), and the other was the natural angle of the elbow.

They used the computerized conformation evaluation method, “Horse Shape Model,” previously used in the work of Thomas Druml, PhD, of the Veterinary University of Vienna Institute of Animal Breeding and Genetics, in Austria. This technique involves advanced digital analysis of photographs taken of horses standing in their natural resting positions.

Gmel’s group scanned photos of more than 200 Lipizzaners and about 300 Franche-Montagne horses. For each horse, they extracted a series of joint angles and compared those angles to data from their genomic analysis of each horse. Previous research revealed the approximate location of genes that code for these angles on the horse genome, so the team narrowed their genomic analysis to 374,070 common SNPs (sections of genes).

The study revealed two significant correlations:

  • A gene (ALX1) associated with cranial (skull) morphology and spine development with the poll angle; and
  • Two potential genes (RSU1 and PTER) associated with bone mineral density and osteoporosis with the elbow angle.

“Currently, the only measure that exists in conformation judging is the horse’s height at the withers,” Gmel said. “Adding measurements of joint angles—especially when there’s a significant genetic link as we’ve found here—can be a useful, objective way to contribute to the evaluation of a horse’s morphology for breeding purposes.

“But these angles also have a very practical sense,” she continued. “For one, the natural angle of a joint may predispose it to injury or make it more likely to break, which would explain the association between joint angles and genes involved in bone density.”

There’s also a question of functionality, Gmel said. “The natural opening of an angle is clearly going to have an effect on a horse’s flexibility at that joint. If we know that, we can modify our riding and training to adapt to that horse’s natural, genetically defined capacities.”

That’s particularly true for the head and neck angle, she added. “The ALX1 gene decides if an individual horse is going to have a more open or closed natural angle at the poll. A horse that’s got a naturally wider angle is going to have more difficulty putting its head and neck into a closed position. If a horse is built that way … he’s going to have certain limitations. Being aware of that can help avoid the welfare consequences of forced equitation positions.”

The group’s next step is to study horse movement in relation to conformation, Gmel said. They also hope to develop a fully automatic system that would allow them to carry out studies like the current one in the field.

The study, “Genome-Wide Association Studies Based on Equine Joint Angle Measurements Reveal New QTL Affecting the Conformation of Horses,” was published in Genes (Basel).