DSLD, or degenerative suspensory ligament desmitis, is a progressive condition in horses where the suspensory ligaments gradually break down and lose their ability to support the fetlock joints. Unlike a typical ligament injury caused by a single event, DSLD involves a slow, irreversible deterioration that worsens over time. It has no cure, and management focuses entirely on keeping affected horses comfortable for as long as possible.
How DSLD Affects the Body
The suspensory ligament runs down the back of each leg and acts as a critical support structure for the fetlock joint, preventing it from hyperextending during movement. In a horse with DSLD, abnormal accumulations of proteoglycans (a type of structural molecule) build up within the ligament tissue, displacing the normal collagen fibers that give the ligament its strength. Over time, this makes the ligament progressively weaker and unable to do its job.
Researchers discovered that this proteoglycan buildup isn’t limited to the suspensory ligaments. It appears in other connective tissues throughout the body, including the nuchal ligament at the back of the neck. Because of this systemic involvement, some researchers have proposed renaming the condition ESPA (equine systemic proteoglycan accumulation) to better reflect that it’s a whole-body connective tissue disorder, not just a leg problem. In practice, most horse owners and veterinarians still use the term DSLD.
Which Breeds Are Most at Risk
DSLD was first described in the Peruvian Horse, which remains the most heavily affected breed. In certain Peruvian Horse bloodlines, prevalence reaches as high as 40%. The condition has since been identified in Arabians, American Saddlebreds, Quarter Horses, Morgans, Thoroughbreds, Paso Finos, Akhal-Tekes, and European Warmbloods.
A large genetic study analyzing over 670,000 genetic markers across 10 breeds categorized breed risk into tiers: Peruvian Horses at the highest risk, Standardbreds, Thoroughbreds, and Quarter Horses at medium risk, Lusitanos and Arabians at low risk, and draft and pony breeds (Belgians, Icelandic Horses, Shetland Ponies, Welsh Ponies) at the lowest risk. The research strongly suggests DSLD is polygenic, meaning many genes contribute to susceptibility rather than a single inherited mutation. Regions on multiple chromosomes showed signatures of selection tied to collagen production, how ligament tissue responds to mechanical stress, and how connective tissue ages. This genetic complexity is one reason there’s no simple screening test for the disease.
Recognizing the Signs
DSLD typically develops gradually, and early signs can be subtle enough to mistake for routine soreness or a mild soft-tissue injury. Horses usually present with a history of lameness along with heat or swelling around the fetlock area. The suspensory ligament itself often feels harder and thicker than normal when palpated, and the horse may react with obvious pain when the area is touched.
As the disease progresses, the hallmark sign emerges: the fetlocks begin dropping closer to the ground as the suspensory ligaments lose their ability to hold the joint in its normal position. In severe cases, the fetlocks can sink so low that the ergot (the small callus at the back of the fetlock) nearly contacts the ground. If the hind limbs are affected, the hock angle gradually straightens, changing the horse’s overall posture.
Horses with DSLD often develop behavioral changes that reflect their discomfort. Some dig holes in their pasture so they can stand with their toes pointed down and heels elevated, a position that takes tension off the suspensory ligament. Others shift their weight constantly or become reluctant to move on hard ground. The condition typically affects multiple limbs, which distinguishes it from a standard suspensory injury that usually involves just one leg.
How Veterinarians Diagnose DSLD
Diagnosis starts with a full lameness exam. Horses with DSLD will be severely lame on affected limbs after a fetlock flexion test, where the veterinarian holds the fetlock in a flexed position for a set period and then watches the horse trot off. Pain on palpation of the suspensory ligament and its branches is another key finding.
Ultrasound imaging is the primary tool for confirming the diagnosis. In a healthy horse, the suspensory ligament appears as a well-organized, uniform structure on ultrasound. In a DSLD horse, the ligament shows visible changes: irregular texture, areas of abnormal density, and often enlargement. These imaging findings, combined with clinical signs in multiple limbs, help distinguish DSLD from a traumatic suspensory injury. Diagnostic criteria for DSLD were formally established in 2005, giving veterinarians a standardized framework to work from.
Because the disease involves systemic proteoglycan accumulation, researchers have also explored using a biopsy of the nuchal ligament as a diagnostic tool. This involves removing a thin sliver of tissue, roughly the size of a human fingernail, from the back of the neck and examining it under a microscope for abnormal proteoglycan deposits. This approach can confirm the systemic nature of the disease without requiring a biopsy from the leg itself.
Managing a Horse With DSLD
There is no treatment that reverses or halts DSLD. Management is palliative, aimed at slowing the progression of discomfort and maintaining quality of life for as long as reasonable. The main strategies involve controlling pain, supporting the limbs mechanically, and modifying the horse’s environment and activity level.
Corrective or supportive shoeing is one of the most common interventions. Farriers may use shoes with extended heels, wedge pads, or other modifications designed to change the angle of the hoof and reduce strain on the suspensory apparatus. The specific approach depends on which limbs are affected and how far the condition has progressed, so close collaboration between the veterinarian and farrier is important.
Turnout management matters considerably. Soft, level footing is easier on compromised ligaments than hard or uneven terrain. Many owners find that affected horses do best on well-maintained grass pastures where they can move at their own pace without being forced into faster gaits. Stall rest, somewhat counterintuitively, is not always beneficial because prolonged standing in one position can increase discomfort in horses dealing with bilateral limb pain.
Anti-inflammatory medications can help manage pain during flare-ups, though long-term use requires veterinary oversight to avoid secondary issues like gastric ulcers. Some owners also explore joint supplements and other supportive therapies, though none have been shown to alter the disease’s course.
Prognosis and Quality of Life
DSLD is a progressive condition, and the trajectory is always downward, though the rate of decline varies widely between individual horses. Some horses remain reasonably comfortable for months or even years with careful management. Others deteriorate more quickly, particularly if all four limbs are involved from the outset.
The most important factor in managing DSLD long-term is honest, ongoing assessment of the horse’s quality of life. Because the condition is degenerative and painful, there comes a point for most affected horses where the discomfort outweighs what management can provide. Horses that can no longer bear weight comfortably, that show persistent signs of distress despite treatment, or whose fetlocks have dropped to the point of mechanical failure are candidates for humane euthanasia. Having regular conversations with your veterinarian about specific benchmarks for your horse helps make that decision clearer when the time comes.
Because of the strong genetic component, breeding decisions also matter. Horses diagnosed with DSLD should not be bred, and prospective buyers of breeds in the higher-risk categories should ask about suspensory health in the horse’s family line.