Research In Action: Searching For Genetic Clues To A Common Neck Abnormality In Horses

An abnormality in the lower neck, found in an estimated 20 to 30 percent of Thoroughbreds and Warmbloods, has become a growing concern among horse owners, fueled at least in part by social media posts linking it to pain, poor performance, and neurologic problems. In some cases, veterinarians say, foals have even been recommended for euthanasia based on the abnormality.

But researchers say that, currently, the science doesn’t support making that determination from an X-ray alone.

“I don’t think it is always benign, but I don’t think we have enough information yet to warrant euthanasia based on radiographs alone,” said Dr. Carrie Finno, professor of genetics at the University of California-Davis School of Veterinary Medicine. “I think we need to figure out what it is that pushes some horses to have performance issues, and others to be fine.”

Finno is leading a Grayson-Jockey Club Research Foundation-funded project investigating the genetics behind the abnormality that was previously termed “TC6-7,” which stands for “transposition of the ventral lamina of C6 onto C7”. This project is a multi-institution project and includes investigators from UC Davis (Drs. Sarah LeJeune, Monica Aleman, and Mathieu Spriet), University of Pennsylvania New Bolton Center (Dr. Amy Johnson), Colorado State University (Dr. Yvette Nout-Lomas), University of Wisconsin-Madison (Drs. Lauren Baker and Sabrina Brouts), and Rood & Riddle Equine Hospital (Dr. Steve Reed).

Normally, C6 has two projections (laminae) extending from its underside that serve as attachment points for muscles and other soft tissues that stabilize the lower neck. In horses with TC6-7, one or both may be absent from C6 and instead appear on C7. The variation can occur on one or both sides, and it doesn’t look exactly the same in every horse.

The TC6-7 abnormality is also sometimes included under the term “equine complex vertebral malformation,” or ECVM, particularly on social media. Finno and Dr. Stephen Reed, an internationally respected equine neurologist at Rood & Riddle Equine Hospital, prefer the more specific TC6-7 terminology.

Reed said the term ECVM draws a comparison with complex vertebral malformation in Holstein cattle, a genetic disorder associated with multiple abnormalities and early death. The equine abnormality is very different, Reed said, and has been documented across multiple breeds, including in horses performing successfully.

Finno’s project could help determine whether a genetic relationship exists between the equine abnormality and the disorder in cattle. But it could also help answer a more practical question: What does finding a TC6-7 abnormality actually mean for a horse?

So far, research hasn’t produced a consistent answer.

A 2024 Colorado State University study of 135 horses undergoing cervical radiographs found the TC6-7 abnormality in 20 percent of the study population. Horses with neck pain were more likely to have the finding, but researchers found no significant association with neurologic disease, cervical orthopedic disease, or lameness.

Other studies have found no association between the abnormality and clinical signs. One study of 377 Warmbloods found C6-C7 variations in 28.6 percent of horses and, notably, found them more frequently in horses without clinical signs than in horses presented with clinical problems. A separate study of 223 Warmbloods found no association between C6-C7 abnormalities and neurologic signs, neck pain or stiffness, or neck-related forelimb lameness.

A study published this year looked at performance instead. Researchers reviewed radiographs and competition records from 200 clinically sound Warmblood sport horses presented for prepurchase examinations. Thirty percent had the abnormality, but researchers found no significant association between the abnormality and competition results.

Reed said he sees plenty of horses with the abnormality that are doing well. On the day he spoke with the Paulick Report, he had examined three horses with the TC6-7 abnormality, all of which were performing successfully.

“My immediate comment is, ‘I am okay with this,’” Reed said. “It does not bother me.”

That doesn’t mean he ignores the finding; Reed tells owners about research that found the abnormality more frequently in horses with neck pain, and he considers it alongside the horse’s clinical presentation and performance.

Reed is particularly interested in whether it matters if the abnormality occurs on just one side. Because muscles attach in the area, Reed wonders whether that asymmetry could change the forces on the vertebrae and contribute to neck pain. For now, that’s a theory, not an established consequence of the TC6-7 abnormality.

This specific abnormality also shouldn’t be confused with cervical vertebral stenotic myelopathy, a neurologic condition commonly known as wobblers syndrome. A horse can have both, Reed said, but having the TC6-7 abnormality doesn’t mean a horse is a wobbler.

“Not every wobbler has this, and not every horse with this is a wobbler,” Reed said.

The distinction matters when an X-ray is being used to make decisions about a horse’s future.

The Equine Spine Initiative, a multidisciplinary group that includes veterinary specialists in neurology, surgery, diagnostic imaging, internal medicine, and sports medicine, has issued a position statement cautioning against making irreversible decisions based solely on radiographs.

“The organization does not support making irreversible clinical decisions, including euthanasia, based solely on radiographic screening findings suggestive of ‘ECVM,’” the group states. The organization notes that ECVM encompasses a variety of congenital abnormalities whose short- and long-term consequences aren’t fully understood.

In other words, an X-ray is one piece of the puzzle.

“You’ve got to look at the whole horse,” Reed said. “You’ve got to look at the clinical side. You’ve got to do proper diagnostics. You need to know more.”

That’s also where Finno’s genetics work could help.

Her immediate goal is to identify genetic variants associated with the TC6-7 abnormality. Researchers have collected DNA and detailed imaging from horses across the country, separating them by the anatomy they display. For example, horses with both ventral laminae absent from C6 and transposed onto C7 are considered separately from horses with unilateral or less complete variations.

If Finno’s team can identify a reliable genetic marker, testing for the abnormality could eventually become much easier. Right now, studying the lower cervical spine requires extensive radiographs, including angled views generally taken at a veterinary clinic. A genetic test would allow researchers to screen much larger populations using DNA samples.

That’s important because one of the biggest unanswered questions is how common the TC6-7 abnormality is among horses that are doing their jobs without a problem.

Finno said researchers could, for example, use DNA to test large numbers of successful show jumping or dressage horses without bringing them into a clinic for cervical radiographs.

“If it’s 30 percent in these horses and they’re doing well, then this [anomaly] alone isn’t necessarily the problem,” Finno said.

A genetic test could eventually have other uses, including screening or informing breeding decisions. But first, Finno said, researchers need to understand what the genetics mean and what relationship, if any, the TC6-7 abnormality actually has with clinical signs.

For now, the presence of this abnormality is one piece of information about a horse, not a prognosis on its own. Reed doesn’t want owners to ignore the finding, but he also doesn’t want them to assume it means a horse can’t have a normal athletic life.

“Most of these horses that have this transposition are totally fine,” he said.

This story was originally published September 22, 2026 at 10:09 AM.