Researchers Confirm Kissing Spines is Hereditary

Kissing spines appears to be hereditary in horses, and scientists are rapidly homing in on the specific areas of the equine genome that are linked to the debilitating condition.

While other factors—such as height, level of work, discipline, sex, age, and saddle fit—probably contribute to the development of the vertebral disease in which spinous processes crowd together, reports one equine research team.

At least two specific chromosomes, Chromosomes 16 and 25, appear to have regions that affect the severity of kissing spines in Warmbloods, Thoroughbreds, and stock horse breeds, said Samantha A. Brooks, PhD, of the Department of Animal Science and the Genetics Institute of the University of Florida, in Gainesville, and Beau Whitaker, DVM, of the Brazos Valley Equine Hospital, in Salado, Texas. A third chromosome, Chromosome 14, seems to have a significant association with the presence—or not—of the disease regardless of its severity. Brooks and Whitaker presented the early results of their study at the 2020 American Association of Equine Practitioners’ Convention, held virtually.

Because of this newly identified genetic component, owners should seriously consider not breeding horses with kissing spines, especially those who have had to retire due to performance issues, said Brooks. Although it’s tempting to repurpose the horse into a breeding animal, “it seems that may perpetuate this kind of problem,” she said.

Brooks, Whitaker, and their fellow researchers have been performing genetic testing on horses with and without kissing spines to locate genes responsible for the disease. The research process is ongoing, but so far they’ve identified loci (areas of groups of genes) that show a clear link to the disease and/or its severity. For example, changes on Chromosome 16 are associated with a difference of one full grade (out of four) of clinical signs of kissing spines, Brooks said. And changes on Chromosome 25 are associated with two full grades. “That is no small difference,” she said. “You can imagine between the two loci you have the possibility of altering that radiographic score by three full scores. And that is indeed quite a change.”

Meanwhile, they noted that certain other factors play more or less of a role. The horse’s height, for example, “has a very, very strong impact,” said Brooks, explaining why vets see greater rates of kissing spines in taller horses (basically, as a horse gets taller and body mass increases, more forces are exerted across the back, and the soft tissue structures supporting the back do not increase in strength accordingly). Sex and age seem to have less significant roles, contrary to what many scientists have previously believed. While their association with kissing spines still exists, they’re apparently “not the major influences we once thought they were,” she said.

The team’s research will hopefully lead to the development of models that help people recognize risk for kissing spines before they buy, breed, or train—as owners could reorient at-risk individuals toward “a less strenuous career,” such as leisure activities, as opposed to upper-level dressage or reining, for example. “Owners would also know at-risk horses and could initiate physical therapy and training regimens known to support the spine in an effort to prevent performance-limiting back pain,” Whitaker told The Horse.

Even so, the scientists cautioned that their research is ongoing and needs more confirmation. Specifically, they said they’re looking for hair samples and identity information (sex, age, breed, height, etc.) on Thoroughbreds, Warmbloods, and stock horses whose X rays show they do not have kissing spines, and they invited owners to submit those to help further the study effort. “We have a lot of work left to do,” Brooks said.

Editor’s Note: Genetic testing was performed and research funding provided by Etalon Inc. Both speakers are consultants for Etalon Inc.