A young Arabian mare’s hind legs have developed straightened hocks, an indicator it has degenerative suspensory ligament desmitis. Researchers at UW-Madison School of Veterinary Medicine are trying to find the DNA marker in order to identify horses carrying the trait.

Using Desiderius Erasmus’ adage “prevention is better than cure” as its guide, a team at UW-Madison School of Veterinary Medicine is researching degenerative suspensory ligament desmitis in horses to determine whether there’s a genetic basis for the disorder. The disease causes leg ligaments to develop abnormal angles in the hocks, fetlocks and pasterns.

Sabrina Brounts, DVM, equine surgeon and sports medicine specialist at UWMVM, is a member of the team looking for a DNA marker for the debilitation condition. If they can identify the marker, they’ll then be able to advise horse owners against using the animals with the DNA for breeding, preventing the disease from being passed on to the next generation.

“This disorder has no cure right now and once a horse is diagnosed, you know that the horse will generally get worse over time,” Brounts said. “It is hard to see these horses in the end stage of the disorder and how hard it is for owners to say goodbye to their horses. If there is anything I can do to help these horses and their owners, I am willing to try.”

The condition tends to be most evident in the hind legs, but can also be seen in the front legs or in all four legs. In the hind legs, the disorder is exhibited by straightened hocks, generally referred to as post-legged. This straightness then results in the fetlocks dropping to the point the pastern is nearly horizontal. In addition to lameness, the disorder can cause heat or swelling in the fetlocks, enlarged fetlocks, windpuffs, arthritis and other secondary conditions. The limbs of horses with DSLD generally worsen as they age.

Before coming to Madison, Brounts received a DVM degree from the University of Utrecht in The Netherlands in Europe. After graduating from the school, she traveled to the United States to continue her surgery training and earn her post-doctoral degree, working at UWMVM for 14 years.

Her special interest in tendon injuries and rehabilitation and the influence of a client led the researcher to get involved in DSLD research.

“This client was a human orthopedic surgeon, who had horses that had DSLD,” Brounts said. “He was interested in finding out why horses got the disease and maybe if we could do something to influence it, slow it down, or maybe even in the end, cure it. So knowing that I was interested in tendon diseases, he contacted me and asked if I was willing to help him in his research. Since we shared a common interest, I said yes. We became friends and that was about eight years ago.”

Since starting the study, Brounts’ friend passed away, but the researcher continues the research in his memory.

Brounts has seen the disorder in horses of various breeds but some breeds seem to have a greater tendency to contract the condition. To conduct the study, the researchers are contacting certain breed association/clubs, breeders and horse owners as well as veterinarians to help them find horses affected with DSLD.

Collecting either hair samples or blood samples of horse affected with DSLD of all breeds has been the first step in identifying the DNA for the disorder. They are first concentrating on the Peruvian Paso since the condition seems to be somewhat prevalent in the breed.

“In the Peruvian Paso horse, we are also collecting DNA samples from horses that are control horses and never have had any tendon injuries in their life,” Brounts said. “These horses have to be over a certain age to become a control horse. Horses are diagnosed with a clinical exam, lameness exam and an ultrasound exam to see where they fall as either an affected case or a control horse.”

Currently the study is concentrating on creating a test to predict which horses are at high risk of getting the disorder.

“That way, breeders could make an informed decision on their breeding practices,” Brounts said. “Social media can be very helpful with this as well. More and more people know we are conducting this research by word of mouth as well, since they have had a horse with DSLD or know of a person that had a horse with DSLD.”

At this time, DSLD can only be definitively diagnosed after the horse has died and tissue taken for examination. The DNA of the affected horses will be compared with that taken from control horses and checked for differences between the samples.

Preliminary data is indicating certain genes are worth noting, but more horses need to be analyzed. After looking at the Peruvian Paso, the study will include other breeds and compare those results with that found in that breed.

“Our ultimate goal is to develop a blood test that we can say your horse is at low-risk, medium risk or high risk of development of the disorder since they carry a certain gene or genes,” Brounts said.

In addition to searching for the DNA marker, the team is also looking at the study horses’ pedigrees. The higher the hereditary factor is the more likely the disorder is passed from the dam or sire. Environmental influences are also being considered.

“If there is an environmental factor part that contributes to the development of the disorder, maybe we can look at that a little closer as well,” Brounts said. “Finally if we know more about the DNA of this disorder and the environment impact, maybe there is a way we can influence the disease by slowing it down or maybe even curing it. That, however, is still a long way from now though.”

Any owners wanting to participate in the study may contact the UWMVM genetics lab by email at genetics@vetmed.wisc.edu.