Degenerative Suspensory Ligament Desmitis (DSLD) is a chronic condition in horses that affects connective tissue, including the suspensory ligament and other ligaments and tendons. This painful condition commonly leads to debilitating lameness.

In horses with DSLD, the suspensory ligament progressively weakens causing hyperextension of the fetlock, hock, and stifle.

The precise causes and mechanisms of DSLD are still an active area of research. Clinical studies are currently aimed at developing accurate, early diagnosis and improving treatment methods.

Research suggests DSLD is at least partially genetically inherited. It was first identified in Peruvian Paso horses and appears to follow family lines. In some families of Peruvian Pasos, it affects up to 40% of horses. [1] This condition has also been identified in Quarter horses, Warmbloods and Arabians. [2]

Unfortunately, there is currently no cure for DSLD and there are no reliable measures to slow disease progression. Supportive care including corrective shoeing, controlled exercise plans and pain relief can help lessen symptoms.

A well-balanced diet to support connective tissue health is recommended for all horses. This includes providing the necessary vitamins and minerals that are required for connective tissue remodelling during growth and repair of the tissue.

What is DSLD?

Ligaments are fibrous connective tissues that span between bones in the body, helping to stabilize them and supporting proper articulation of the joints. In horses, the top of the suspensory ligament attaches to the rear of the cannon bone and the pastern bone beneath.

At this point, the ligament separates into two strands surrounding the sesamoid bones. Think of the suspensory ligament as having an inverted Y shape.

Degenerative Suspensory Ligament Desmitis in Horses | Mad Barn Canada

A common feature of Degenerative Suspensory Ligament Desmitis is an accumulation of proteoglycans in the space between cells making up the ligament.

Proteoglycans are naturally occurring glycosylated proteins found in connective tissue. They are made up of proteins bound to other molecules such as chondroitin sulfate.

These proteins are found outside of the cells and form the extracellular matrix. Proteoglycans help to provide structural support for cells in ligaments, but an excess of these proteins can actually weaken connective tissues.

In horses with DSLD, there is an excess accumulation of proteoglycans and they are of altered composition. This accumulation affects mobility of the joint, leading to progressive and painful lameness. [1]

Even someone unfamiliar with equines can spot a horse suffering from severe DSLD. In advanced cases, the fetlocks drop so much that it may look like the animal is walking on them.

A Systemic Disorder?

DSLD was not recognized as a specific disorder until the late 20th century. Once considered an “old horse” disease, DSLD is now recognized as a connective tissue disorder affecting the entire body.

In 2006, researchers at the University of Georgia found that DSLD was not limited to the suspensory ligaments of affected equines. They determined it was a systemic disorder, “involving tissues and organs with significant connective tissue component“.

It is also referred to as Equine Systemic Proteoglycan Accumulation (ESPA) to reflect the systemic nature of this condition. [3]

The tissues and organs from 28 affected horses, all but six of them Peruvian Pasos, were examined, along with tissues and organs from eight control animals. The presence of excess amounts of proteoglycans was found in: [3]

  • Suspensory ligaments
  • Deep flexor tendons
  • Superficial flexor tendons
  • Patellar ligaments
  • Nuchal ligaments
  • Cardiovascular system
  • Tissues of the eye

Gel chromatography performed on tendon extracts revealed the presence of excess proteoglycans in the affected horses. The control group did not have these excess proteoglycans.

Research is ongoing to identify how this accumulation of proteoglycans arises in the hopes of finding a biomarker of DSLD that can identify affected horses before symptoms appear. [2]

Early detection could help to implement treatment protocols to slow the progression of symptoms and assist in controlled breeding practices to avoid producing offspring with this genetic disorder.