What is DSLD?
Degenerative Suspensory Ligament Desmitis (DSLD), now more accurately termed Systemic Proteoglycan Accumulation (SPA), represents a progressive, degenerative connective tissue disorder affecting horses. This debilitating condition primarily impacts the suspensory ligaments—critical structures that support the fetlock joints and bear substantial weight during movement. However, research has revealed that DSLD extends far beyond isolated ligament damage, affecting connective tissues throughout the entire body, which is why the medical community increasingly prefers the term SPA.
We recognize DSLD as one of the most challenging and heartbreaking conditions in equine medicine. Unlike acute injuries that may heal with appropriate treatment, DSLD involves progressive deterioration of connective tissue that cannot be reversed. The suspensory ligaments gradually lose their structural integrity, becoming weakened and elongated, leading to characteristic dropped fetlocks, lameness, and eventually severe disability. Understanding this complex disease proves essential for horse owners, breeders, and veterinary professionals working to manage affected horses and potentially reduce disease incidence through informed breeding decisions. Here is s link to a video we made showing horses in different stages of DSLD.
The Suspensory Apparatus and Its Function
To fully comprehend DSLD, we must first understand the suspensory apparatus and its critical role in equine locomotion. The suspensory ligament originates at the back of the cannon bone, runs down the back of the leg, and branches into two parts that attach to the sesamoid bones behind the fetlock joint. These ligaments then continue downward, joining with other structures to support the pastern and coffin joints.
During weight-bearing and movement, the suspensory ligament acts as a spring mechanism, absorbing shock and preventing hyperextension of the fetlock joint. When horses move, particularly at speed or over jumps, enormous forces transfer through these ligaments. In healthy horses, the suspensory ligament’s elastic properties allow it to stretch and recoil efficiently, protecting joints and bones from excessive stress. The ligament must be both strong enough to support the horse’s weight and flexible enough to accommodate the dynamic forces of movement.
When DSLD compromises the suspensory ligament’s structural integrity, this critical support system fails progressively. The ligament becomes unable to prevent excessive fetlock drop, leading to the characteristic postural changes and lameness associated with the disease.
What Causes DSLD?
The underlying cause of DSLD involves abnormal proteoglycan metabolism within connective tissues throughout the body. Proteoglycans are large molecules composed of proteins attached to chains of glycosaminoglycans (GAGs), which provide structural support and elasticity to connective tissues including ligaments, tendons, blood vessel walls, and skin.
In horses with DSLD, these proteoglycans accumulate abnormally within connective tissues rather than being properly organized into functional structures. This accumulation disrupts the normal architecture of collagen fibers and elastin, the proteins responsible for tissue strength and flexibility. As abnormal proteoglycans infiltrate the suspensory ligament, the tissue loses its biomechanical properties, becoming weaker and more prone to elongation and eventual breakdown.
Research strongly suggests genetic predisposition plays a primary role in DSLD development. Certain breeds demonstrate significantly higher incidence rates, indicating hereditary transmission of the condition. Peruvian Pasosshow particularly high prevalence, with some studies suggesting up to 20% of the breed may be affected. Other breeds with elevated DSLD rates include Paso Finos, Arabians, American Quarter Horses, Thoroughbreds, and various warmblood breeds. The existence of familial lines with multiple affected individuals provides compelling evidence for genetic inheritance patterns.
Scientists continue investigating the specific genetic mutations responsible for DSLD. Recent research has identified potential candidate genes involved in proteoglycan synthesis and connective tissue formation. Understanding the genetic basis of DSLD may eventually enable development of genetic testing to identify carriers before breeding, potentially reducing disease prevalence in future generations.
While genetics appears to be the primary causative factor, various triggering events or contributing factors may influence when and how severely the disease manifests. These potential triggers include:
Age and cumulative stress influence disease progression. While DSLD can affect horses of any age, clinical signs typically emerge in middle-aged to older horses, suggesting that years of accumulated mechanical stress may accelerate deterioration of genetically compromised tissue. However, we also observe cases in young horses, indicating that genetic factors can override the protective effects of youth.
Mechanical stress and workload may exacerbate underlying genetic susceptibility. Horses in demanding athletic disciplines face greater forces through their suspensory ligaments, potentially hastening clinical disease development in genetically predisposed individuals. However, DSLD also affects pasture-kept horses with minimal athletic demands, confirming that mechanical stress alone does not cause the disease in horses without genetic predisposition.
Metabolic and endocrine factors may influence disease expression. Some researchers have investigated potential connections between DSLD and conditions like equine metabolic syndrome or pituitary pars intermedia dysfunction (PPID/Cushing’s disease), though definitive relationships remain unproven. Hormonal changes associated with pregnancy, lactation, or advancing age might theoretically affect connective tissue metabolism.
Nutritional factors have been investigated as potential contributors, though no specific dietary deficiencies or excesses have been definitively linked to DSLD development. Some practitioners recommend nutritional supplements supporting connective tissue health, though scientific evidence for prevention or treatment remains limited.
Clinical Signs and Symptoms
DSLD produces a constellation of characteristic clinical signs reflecting progressive connective tissue deterioration. The disease typically presents initially with subtle changes that gradually worsen over months to years.
Lameness represents the most common presenting complaint. Early in the disease, horses may demonstrate mild, intermittent lameness that worsens with exercise. The lameness often appears vague or shifting between limbs, making diagnosis challenging. As the disease progresses, lameness becomes more consistent and severe. Affected horses develop a characteristic shortened, stiff gait described as “pottery” or “walking on eggshells.” They demonstrate reluctance to move, particularly on hard or uneven surfaces.
Dropped fetlocks constitute the hallmark physical sign of advanced DSLD. As the suspensory ligaments lose their supporting function, the fetlock joints sink lower toward the ground, particularly noticeable when the horse bears weight. In early disease, fetlock drop may be subtle and visible only after exercise or when standing on hard surfaces. Progressive cases develop profound fetlock hyperextension, with the back of the fetlock approaching or even touching the ground. This excessive drop may affect forelimbs, hindlimbs, or all four legs, though hindlimbs are often more severely affected initially.
Thickening and enlargement of the suspensory ligament can be palpated during physical examination. The normally defined ligament becomes diffusely swollen, firm, and sometimes painful to pressure. However, unlike acute suspensory ligament injuries that produce localized inflammation and heat, DSLD-affected ligaments typically feel cool despite their enlargement.
Postural changes develop as horses attempt to compensate for discomfort and instability. Affected horses often stand with their limbs positioned abnormally, sometimes placing feet forward to reduce fetlock hyperextension. They may shift weight frequently, demonstrating reluctance to bear weight normally on affected limbs. Some horses develop a “sawhorse” stance with all four legs positioned wider than normal and fetlocks dropped.
Heat and swelling around the fetlock region may occur, though less consistently than with acute injuries. Some horses develop windpuffs (fluid accumulation in the fetlock joint or tendon sheath) secondary to chronic instability and inflammation.
Behavioral changes accompany chronic pain. Previously willing horses may become reluctant to work, resistant to movement, or irritable when asked to perform. Many affected horses demonstrate depression, decreased appetite, and reduced interest in their surroundings as the disease progresses.
Systemic signs reflecting the widespread nature of connective tissue involvement may develop. These include:
- Skin changes: The skin may lose elasticity, appearing loose or developing unusual texture. Some horses develop abnormal scarring or slow wound healing.
- Blood vessel fragility: Abnormal proteoglycan accumulation in blood vessel walls can lead to hemorrhages, visible as pinpoint bleeding in mucous membranes or unexplained bruising.
- Ocular abnormalities: Some affected horses develop changes in eye tissues, including lens luxation or other structural abnormalities.
- Reproductive issues: Mares may experience difficulty maintaining pregnancies or complications during foaling related to compromised connective tissue integrity.
Progressive deterioration characterizes the disease course. While the rate of progression varies considerably between individuals, DSLD inevitably worsens over time. Some horses decline gradually over years, while others deteriorate rapidly within months of initial diagnosis. The unpredictable progression rate creates significant management challenges and emotional difficulty for owners.
Diagnostic Approaches
Diagnosing DSLD requires combining clinical findings, diagnostic imaging, and histopathological confirmation, though definitive diagnosis during life remains challenging.
Physical examination provides essential initial information. Veterinarians assess gait abnormalities, palpate suspensory ligaments for thickening or pain, evaluate fetlock conformation and drop, and perform flexion tests. The characteristic combination of bilateral involvement, fetlock hyperextension, and diffusely thickened suspensory ligaments raises strong suspicion for DSLD.
Ultrasonographic examination of the suspensory ligaments reveals characteristic abnormalities. In healthy ligaments, ultrasound shows organized linear fiber patterns with uniform echogenicity (brightness). DSLD-affected ligaments display loss of normal fiber pattern, areas of decreased echogenicity, and diffuse enlargement affecting the entire ligament rather than localized injury zones typical of traumatic injuries. The body of the suspensory ligament (the portion between the origin and branches) often shows particularly striking changes.
Unlike acute injuries showing inflammation and active damage, DSLD ligaments demonstrate chronic degenerative changes without significant inflammatory response. Serial ultrasound examinations over time may reveal progressive deterioration despite rest and treatment, supporting DSLD diagnosis over acute injury.
Radiographs (X-rays) of the fetlock joints help evaluate secondary changes including fetlock joint remodeling, sesamoid bone changes, and degree of fetlock hyperextension. While radiographs cannot visualize soft tissues like ligaments, they provide valuable information about skeletal changes resulting from chronic instability.
Magnetic resonance imaging (MRI) offers superior soft tissue visualization compared to ultrasound, though expense and limited availability restrict its routine use. MRI can reveal proteoglycan accumulation and structural changes throughout the suspensory apparatus and surrounding tissues.
Histopathological examination provides definitive diagnosis but requires tissue biopsy, an invasive procedure with inherent risks. Pathologists examine tissue samples under microscopy, looking for characteristic proteoglycan accumulation and disrupted collagen architecture. Special staining techniques highlight abnormal proteoglycan deposits, confirming DSLD diagnosis. However, many practitioners and owners elect to forgo biopsy when clinical and imaging findings strongly support diagnosis, avoiding additional stress and risk to the horse.
Exclusion of alternative diagnoses forms an important component of the diagnostic process. Other conditions producing similar signs include:
- Acute suspensory ligament injury: Typically unilateral or asymmetric, with history of acute onset, localized ultrasonographic changes, and potential for improvement with rest
- Chronic degenerative joint disease: May produce fetlock changes but typically shows radiographic joint pathology and responds differently to treatment
- Flexural deformities: Can produce postural changes but have different underlying pathology and presentation patterns
- Neurological conditions: May cause gait abnormalities but lack the characteristic ligament changes and fetlock hyperextension
Experienced equine veterinarians consider the entire clinical picture, including breed predisposition, age, pattern of involvement, response to rest, and characteristic imaging findings when making DSLD diagnoses.
Treatment and Management
Currently, no cure exists for DSLD, and treatment focuses on managing pain, slowing progression when possible, and maintaining quality of life for as long as feasible. We emphasize that treatment approaches remain largely supportive and empirical, as limited research exists evaluating specific interventions’ effectiveness.
Pain management constitutes the primary treatment goal. Various medications help control discomfort:
- Non-steroidal anti-inflammatory drugs (NSAIDs) like phenylbutazone (“bute”), flunixin meglumine (Banamine), or firocoxib (Equioxx) provide pain relief and reduce inflammation. Long-term NSAID use requires monitoring for potential adverse effects including gastrointestinal ulcers and kidney damage.
- Gabapentin and other neuropathic pain medications may benefit horses experiencing nerve-related pain components.
- Pentosan polysulfate injections have been used by some practitioners, theorizing potential benefits for connective tissue health, though scientific evidence supporting effectiveness in DSLD remains limited.
- Adequan (polysulfated glycosaminoglycan) represents another injectable medication some veterinarians employ, hoping to support remaining healthy connective tissue.
Corrective shoeing and hoof care play crucial roles in management. Farriers working with DSLD horses aim to provide maximum support while accommodating progressive fetlock drop:
- Supportive shoeing using shoes with extended heels, wedges, or specialized support shoes helps prevent excessive fetlock hyperextension.
- Regular trimming maintains proper hoof balance, reducing abnormal stresses on compromised ligaments.
- Glue-on shoes may benefit horses with severe fetlock drop where nailing shoes becomes difficult or painful.
Physical therapy and controlled exercise require careful balance. Complete stall rest may lead to muscle atrophy and joint stiffness without slowing disease progression. Conversely, excessive exercise accelerates tissue damage. Most practitioners recommend:
- Turnout in small paddocks allowing gentle movement without running or playing
- Hand-walking providing controlled, low-impact exercise
- Avoiding strenuous activity, jumping, or work on hard or uneven surfaces
- Swimming or water treadmill exercise when available, providing low-impact cardiovascular conditioning
Nutritional support focuses on maintaining healthy body weight and potentially supporting connective tissue health:
- Appropriate body condition: Overweight horses place excessive stress on compromised ligaments, while underweight horses lack reserves to cope with chronic disease. Maintaining moderate body condition proves optimal.
- Quality forage-based diet: Ensuring adequate nutrition supports overall health without excessive caloric intake.
- Supplements: Various supplements containing ingredients like vitamin C, copper, zinc, manganese, amino acids, or specialized proteoglycan precursors are marketed for connective tissue support. While these products may provide nutritional insurance, scientific evidence proving specific benefits in DSLD remains limited. We recommend discussing supplementation with your veterinarian before starting any products.
Regenerative therapies including platelet-rich plasma (PRP), stem cell therapy, or other biologic treatments have been attempted in DSLD cases with variable and generally disappointing results. Unlike traumatic injuries where these therapies may promote healing, DSLD involves progressive genetic disease where underlying tissue continues degenerating despite treatment. Some horses may experience temporary improvement, but long-term progression continues.
Environmental modifications enhance affected horses’ comfort and safety:
- Deep, soft bedding in stalls reduces pressure on dropped fetlocks
- Level, firm footing in turnout areas prevents stumbling and provides stable surface for compromised legs
- Easy access to food and water reduces movement requirements for horses with severe mobility limitations
- Companionship meets horses’ social needs while avoiding situations where affected horses might be injured by herdmates during play
Bandaging or wrapping affected limbs requires caution. While some practitioners recommend supportive wrapping, improperly applied bandages can cause more harm than benefit. If wrapping is employed, proper technique and regular monitoring prevent bandage-related complications.
Prognosis and Quality of Life Considerations
The prognosis for horses with DSLD is unfortunately poor to grave. While the disease progression rate varies considerably, all affected horses eventually deteriorate to the point where quality of life can no longer be maintained.
Disease progression timelines vary dramatically:
- Some horses decline rapidly, becoming severely disabled within 6-12 months of diagnosis
- Others maintain reasonable comfort and function for several years with aggressive management
- Most fall somewhere between these extremes, experiencing gradual progression over 1-3 years
Quality of life assessment becomes increasingly important as disease advances. Horse owners face difficult decisions balancing treatment efforts with animal welfare. We encourage regular, honest evaluation of affected horses’ quality of life considering:
- Pain levels: Can pain be adequately controlled with available medications? Is the horse comfortable at rest and during gentle movement?
- Mobility: Can the horse move safely to access food, water, and shelter? Is the horse at risk of falling or becoming cast?
- Behavior and attitude: Does the horse maintain interest in surroundings, eat willingly, and demonstrate some enjoyment in life?
- Management requirements: Are treatment needs reasonable and sustainable, or has care become extremely demanding and stressful for both horse and owner?
Many horse owners find it helpful to identify specific quality-of-life criteria in advance, determining what changes would indicate humane euthanasia has become appropriate. This proactive approach, while emotionally difficult, helps guide decisions during stressful times when objectivity proves challenging.
Euthanasia represents the most humane option when horses can no longer maintain acceptable quality of life despite maximal treatment efforts. Signs indicating euthanasia may be appropriate include:
- Uncontrollable pain despite aggressive medication
- Inability to stand or move safely
- Recurrent falling or inability to rise without assistance
- Severe, progressive weight loss despite adequate nutrition
- Obvious suffering or loss of will to continue
We emphasize that choosing euthanasia when quality of life can no longer be maintained represents a final act of compassion, preventing unnecessary suffering. While always difficult, this decision honors the relationship between horse and owner and prioritizes the horse’s welfare above human wishes to extend life at any cost.
Impact on Different Horse Populations
DSLD affects various horse populations differently, with implications for breeding, competition, and long-term management.
Breeding stock: Discovering DSLD in breeding animals creates difficult ethical and practical dilemmas. Given the strong genetic component, affected horses and their close relatives should ideally be removed from breeding programs to reduce disease transmission. However, genetic testing capable of identifying carriers before clinical signs develop remains unavailable, complicating breeding decisions. We strongly encourage breeders to:
- Track DSLD cases within their breeding programs
- Avoid breeding horses diagnosed with DSLD
- Carefully consider breeding decisions for close relatives of affected horses
- Support research efforts developing genetic testing
- Prioritize transparency within breed communities about DSLD occurrence
Performance horses: Active competition horses developing DSLD face immediate retirement. The progressive nature of the disease combined with increased biomechanical demands of athletic work makes continued competition impossible and potentially dangerous. Early retirement preserves remaining quality of life and prevents catastrophic breakdown during work.
Companion horses: Horses maintained as companions or in light recreational roles may continue relatively comfortable lives longer than competition horses, as reduced athletic demands lessen stress on compromised ligaments. However, eventual progression necessitates retirement and supportive care.
Rescue and rehabilitation populations: Organizations acquiring horses with unknown histories should remain vigilant for DSLD signs, as affected horses may be relinquished when disabilities emerge. Rescue groups need realistic expectations about long-term care requirements and prognosis when accepting potentially affected horses.
Research Directions and Future Possibilities
Ongoing research seeks to improve understanding of DSLD pathophysiology, develop better diagnostic tools, identify genetic markers, and discover effective treatments.
Genetic research aims to identify specific mutations responsible for DSLD susceptibility. Once causative genes are identified, development of genetic testing would enable:
- Identification of carriers before breeding
- Informed breeding decisions reducing disease prevalence
- Earlier diagnosis in at-risk horses before clinical signs develop
- Targeted treatment approaches based on specific genetic variants
Pathophysiology research investigates the cellular and molecular mechanisms driving abnormal proteoglycan metabolism. Understanding these processes might reveal therapeutic targets for interventions preventing or slowing disease progression.
Treatment studies evaluate various management approaches systematically, providing evidence-based guidance currently lacking. Well-designed trials assessing medications, supplements, physical therapies, and regenerative treatments would help practitioners and owners make informed treatment decisions.
Biomarker development seeks blood tests or other non-invasive methods for early diagnosis and progression monitoring. Currently, definitive diagnosis requires invasive tissue biopsy or relies on advanced clinical signs. Earlier detection through biomarkers would enable prompt intervention and research on early-stage disease.
Epidemiological studies tracking DSLD prevalence across breeds, geographic regions, and management systems improve understanding of risk factors and disease distribution. This information guides breeding recommendations and management modifications potentially reducing disease impact.
Prevention Strategies
Given the genetic basis of DSLD, prevention primarily involves selective breeding practices designed to reduce transmission of susceptibility genes through horse populations.
Breed registry involvement: Some breed organizations have begun acknowledging DSLD as a significant health concern and implementing programs tracking affected horses. Transparency and data collection within breed registries enable informed breeding decisions and support research efforts.
Breeder responsibility: Individual breeders bear primary responsibility for making ethical breeding decisions that prioritize genetic health. This includes:
- Removing diagnosed horses from breeding programs
- Carefully evaluating whether to breed siblings or offspring of affected horses
- Maintaining records of DSLD cases within breeding lines
- Being transparent with buyers about DSLD history in related horses
Buyer awareness: Prospective horse buyers, particularly those interested in breeds with elevated DSLD prevalence, should inquire about disease history in the horse’s lineage. While no guarantee exists that horses from unaffected lines won’t develop DSLD, avoiding horses with known affected relatives reduces risk.
Management factors, while not preventing genetically determined disease, may influence when and how severely signs develop:
- Avoiding obesity reduces stress on ligaments
- Appropriate conditioning without excessive demands balances fitness with joint preservation
- Quality nutrition supports overall tissue health
- Appropriate hoof care maintains proper limb biomechanics
Living with a DSLD Horse
Owners of horses diagnosed with DSLD face significant emotional, practical, and financial challenges. We offer guidance for those navigating this difficult journey.
Emotional support: DSLD diagnosis generates grief, frustration, and sense of helplessness. Connecting with other owners managing DSLD horses through online communities or local support networks provides emotional support and practical advice. Many owners find counseling helpful when facing progressive disease and eventual loss.
Financial planning: DSLD management incurs ongoing expenses including medications, specialized shoeing, veterinary monitoring, and potentially end-of-life costs. Planning for these expenses helps ensure affected horses receive appropriate care throughout their remaining time.
Day-to-day management: Establishing routines maximizing comfort and safety while maintaining quality of life requires ongoing adjustment as disease progresses. Flexibility and willingness to modify approaches as needs change proves essential.
Recognizing small joys: While living with progressive disease presents challenges, many owners find meaning in providing compassionate care, maintaining their horses’ dignity, and appreciating good days when they occur. Focusing on quality rather than quantity of remaining time helps owners and horses make the most of their time together.
Planning for the end: Advance planning for euthanasia, including financial arrangements and decisions about body disposition, reduces stress when difficult decisions must be made. Having these conversations with veterinarians and family members before crisis situations arise enables more thoughtful, less emotionally fraught decision-making.
Conclusion
Degenerative Suspensory Ligament Desmitis (DSLD), now better understood as Systemic Proteoglycan Accumulation, represents a devastating genetic disease affecting connective tissues throughout horses’ bodies. This progressive condition, characterized by breakdown of the suspensory ligaments and resulting fetlock hyperextension, lameness, and disability, carries a poor prognosis with no current cure available.
Understanding DSLD’s genetic basis emphasizes the critical importance of responsible breeding practices that prioritize genetic health. As research continues investigating the molecular mechanisms underlying this disease, we hope for future development of genetic testing enabling identification of carriers and ultimately reduction of DSLD prevalence through selective breeding.
For owners of affected horses, management focuses on maximizing comfort and quality of life through pain control, supportive shoeing, appropriate exercise modification, and environmental management. While the progressive nature of DSLD inevitably leads to difficult end-of-life decisions, compassionate care throughout the disease course honors the bond between horses and their people.
We encourage continued support for research initiatives investigating DSLD, increased transparency within breeding communities about disease occurrence, and compassionate, realistic approaches to managing affected horses that prioritize animal welfare above all other considerations.