Kissing spine in horses does appear to have a genetic component. A genome-wide association study identified specific genetic markers on chromosome 25 that correlate with the severity of the condition, and certain breeds are consistently more susceptible. However, genetics is only one piece of the puzzle. Training, saddle fit, core strength, and conformation all play a role in whether a horse develops clinical signs.
What Kissing Spine Actually Is
Kissing spine, formally called overriding dorsal spinous processes (ORDSP), happens when the bony projections along the top of a horse’s spine crowd together. In a healthy back, these projections have at least 4 mm of space between them. In horses with kissing spine, that gap narrows until the bones touch, overlap, or even fuse together. This contact creates pain, inflammation, and sometimes bone remodeling at the points of contact.
The condition is graded on a four-point scale. Grade 1 means the spaces between the spine’s projections are narrowing. Grade 2 involves thickening of the bone edges. Grade 3 shows bone loss along the margins, and grade 4 means severe remodeling of the bone. Importantly, the radiographic appearance doesn’t always match the clinical picture. Studies using X-rays and postmortem exams have found anatomical signs of the condition in up to 92% of horses examined, yet many of those horses never show pain or performance problems.
The Genetic Evidence So Far
The strongest genetic evidence comes from a study that examined 155 stock-type and Warmblood horses using both clinical evaluation and DNA analysis. Researchers genotyped each horse using a chip that reads over 61,000 individual genetic markers spread across the horse’s genome. They then compared those genetic profiles against each horse’s kissing spine severity grade.
Two genetic markers on chromosome 25 showed a significant association with the condition. The region those markers define contains roughly 17 protein-coding genes. The most strongly associated marker showed a clear dose effect: for each copy of a particular gene variant a horse carried, its kissing spine grade increased by one level on average. A horse with two copies of that variant would, statistically, score two grades higher than a horse with none.
Notably, the study found no significant effect from breed group, age, height, or sex once the genetic markers were accounted for. That suggests the genetic variant itself, rather than breed as a broad category, is the more precise predictor of risk. This is still preliminary work based on a relatively small sample, but it points toward a real, measurable genetic contribution to kissing spine severity.
Why Certain Breeds Are More Affected
Even before genetic testing entered the picture, veterinarians noticed that kissing spine clusters in certain breeds. Warmbloods, Thoroughbreds, and Quarter Horses are consistently identified as more susceptible. UC Davis’s veterinary school lists all three as particularly at risk.
This breed pattern makes sense in light of the genetic findings. If specific gene variants increase susceptibility, and those variants are more common in certain breed populations due to selective breeding for performance traits, then the condition will naturally appear more often in those breeds. Warmbloods and Thoroughbreds have been bred for athletic movement with particular back conformations, and Quarter Horses have been selected for compact, muscular builds. These breeding pressures may have inadvertently concentrated genetic variants that predispose horses to narrower interspinous spacing.
Environmental Factors Still Matter
Genetics loads the gun, but environment pulls the trigger. A horse can carry genetic risk factors for kissing spine and never develop clinical signs, or it can have mild anatomical changes that become painful only under certain conditions. Several non-genetic factors influence whether the condition becomes a problem.
Core muscle strength plays a major role. Horses that work with a lifted, rounded back create more space between the spinous processes. Horses that hollow their backs under saddle compress those spaces. Poor saddle fit can force a horse into a hollow posture, concentrating pressure on the thoracolumbar region where kissing spine most commonly occurs. The level and type of work matters too. Horses asked to perform collected movements or jump at higher levels place different demands on the spine than trail horses working on a loose rein.
Age and fitness are factors as well. Young horses that are started too quickly under saddle without adequate conditioning may develop problems earlier if they already carry anatomical predispositions. Conversely, older horses with years of compensatory movement patterns may gradually develop clinical signs from changes that were present but silent for years.
What This Means for Breeding Decisions
No breed association currently requires genetic testing or radiographic screening for kissing spine before breeding. This stands in contrast to conditions like osteochondrosis, where some registries do factor radiographic findings into breeding approvals. The genetic research is still too early-stage for a validated commercial test, and the high radiographic prevalence of the condition (up to 92% showing some degree of change) makes it difficult to draw a clean line between “affected” and “unaffected.”
Still, the identification of a specific chromosomal region opens the door for future screening tools. If you’re choosing a breeding stallion or deciding whether to breed a mare with a history of back pain, knowing that kissing spine has a genetic dimension is worth weighing. A horse with severe, clinically significant kissing spine may pass along genetic risk to its offspring, particularly if bred to another horse from a susceptible line.
Separating Radiographic Findings From Real Problems
One of the trickiest aspects of kissing spine is that what shows up on X-rays doesn’t always match what the horse feels. Many horses with narrowed or touching spinous processes perform normally and never show signs of back pain. Others with relatively mild radiographic changes are clearly uncomfortable. This disconnect makes it hard to use genetics or imaging alone to predict which horses will have performance-limiting problems.
The genome-wide association study specifically focused on “performance-limiting” kissing spine, meaning horses that were clinically affected, not just radiographically abnormal. That distinction matters. The genetic markers identified may be more closely tied to the painful, progressive form of the condition rather than the benign anatomical variation that so many horses carry without consequence. If future research confirms this, genetic testing could eventually help distinguish horses at risk for real problems from those who simply have close spinous processes but will never need treatment.