Bit & Bridle

Equine Lymphangitis

Other Names

  • Big Leg Disease
  • Monday-Morning Disease (archaic)
  • Ulcerative Lymphangitis (a specific chronic bacterial form)
  • Sporotrichosis (when caused by Sporothrix schenckii)

What is Lymphangitis in Horses?

Lymphangitis is an inflammation of the lymphatic vessels, most commonly causing dramatic, sudden swelling of one or more limbs — most frequently a hindlimb. The lymphatic system is responsible for draining excess tissue fluid back into the bloodstream. When the lymphatic vessels become inflamed or obstructed, fluid accumulates in the affected limb, causing the profound, painful swelling that gives the condition its colloquial name “Big Leg Disease.”

Equine lymphangitis should not be confused with simple “filled legs” or pitting oedema that occurs mildly in horses after box rest or reduced exercise — that is a benign, mechanical phenomenon. True lymphangitis involves active inflammation of the lymphatic system, significant pain, heat, and often systemic illness. It requires urgent veterinary treatment and can have serious, long-term consequences for the affected limb if not managed promptly and aggressively.

Lymphangitis can be caused by bacterial infection (the most common form in horses), fungal infection, parasitic infection, or in some cases has no identifiable infectious cause and may represent an immune-mediated reaction. It can present as an acute (sudden onset, single episode) or chronic, recurring condition.

Causes

The most common cause of acute lymphangitis in horses is a bacterial infection, typically following a wound, skin abrasion, or penetration of the skin that allows bacteria to enter the lymphatic system:

  • Bacterial infection: Staphylococcus spp., Streptococcus spp., Corynebacterium pseudotuberculosis, and other organisms. Entry is usually through small skin wounds, especially in the lower limb.
  • Chronic ulcerative lymphangitis: A specific form caused primarily by Corynebacterium pseudotuberculosis (also responsible for Pigeon Fever in horses), characterised by ulcerating nodules along the medial aspect of the hindlimb and a chronic, relapsing course.
  • Fungal lymphangitis (Sporotrichosis): Caused by Sporothrix schenckii; produces nodular skin lesions that ulcerate and discharge along lymphatic channels. Rare in the UK but has zoonotic potential.
  • Parasitic lymphangitis: Microfilarial or other parasitic causes — rare in the UK but seen in endemic tropical regions
  • Immune-mediated: In some horses, episodes of severe limb swelling and lymphangitis occur without a clearly identifiable infectious cause and may represent an exaggerated immune response

Risk factors include minor wounds (particularly on the lower limb or coronary band), compromised skin from chronic dermatitis (such as mud fever), poor limb conformation, and reduced exercise.

Symptoms and Signs

Acute lymphangitis typically presents dramatically and rapidly:

  • Sudden-onset, severe swelling of one limb — most commonly a hindlimb. The swelling can be enormous, extending from the coronary band to the stifle or beyond.
  • Intense heat in the swollen limb
  • Severe lameness — the horse may be three-legged lame and reluctant to bear any weight
  • Pain on palpation of the limb
  • Pitting oedema: pressing the swollen tissue with a finger leaves a temporary indentation
  • Systemic illness: fever (39–41°C), depression, reduced appetite, and increased heart rate in many cases
  • Seeping or weeping of serum through the skin surface in severe cases
  • Visible cordlike thickening of lymphatic vessels along the medial aspect of the limb in chronic or recurrent cases
  • Skin ulceration and discharging tracts in ulcerative lymphangitis

Diagnosis

Diagnosis is based on clinical signs and supported by appropriate investigations:

  • Clinical examination: The dramatic, sudden limb swelling with heat, pain, and systemic signs in a horse without prior history of limb filling is highly characteristic
  • Blood tests: Haematology typically shows leucocytosis (elevated white cell count) and elevated inflammatory markers supporting active infection or inflammation
  • Culture and sensitivity: Swabs from any wound or skin break in the area, or aspirates from any lymph node or ulcerating lesion, to identify the causative organism and guide antibiotic selection
  • Ultrasound: Can visualise lymphatic vessel inflammation, fluid accumulation, and any deeper abscess formation
  • Skin biopsy: For chronic, ulcerative, or suspected fungal forms, histopathology and fungal culture may be required
  • Differentials: Septic arthritis of the fetlock or hock, severe cellulitis, deep abscess, clostridial myositis, and vasculitis must be distinguished — all require different management

Treatment

Acute lymphangitis is an urgent veterinary condition requiring prompt and aggressive treatment:

  • Systemic antibiotics: Broad-spectrum antibiotics (commonly penicillin and gentamicin, or trimethoprim-sulphonamide combinations) initiated promptly, ideally after culture samples have been obtained. Treatment continues for 7-14 days minimum.
  • NSAIDs: Essential for reducing pain, fever, and inflammation. Phenylbutazone or flunixin meglumine are commonly used.
  • Diuretics: Frusemide (furosemide) may be used in the acute phase to help reduce the severe fluid accumulation
  • Hydrotherapy: Cold hosing or ice therapy two to three times daily in the acute phase reduces pain and inflammation
  • Compression bandaging: Light support bandaging — applied carefully by someone experienced in equine bandaging — helps move fluid proximally and supports the swollen tissue
  • Controlled exercise: Gentle hand-walking, as soon as pain allows, is critical to stimulate lymphatic drainage. Prolonged box rest worsens fluid stasis.
  • Topical treatments: DMSO-based gels or topical anti-inflammatory preparations may assist local inflammation reduction

Prevention

  • Manage all limb wounds promptly and thoroughly — even small abrasions on the lower limb can serve as entry points for bacteria, and are the wounds most prone to proud flesh and delayed healing
  • Address mud fever and other skin infections of the lower limb aggressively to prevent a portal of entry for bacteria
  • Ensure regular exercise or turnout — horses with restricted movement are more prone to lymphatic stasis and subsequent episodes
  • Monitor horses prone to recurrence closely after wet, muddy conditions or heavy workloads
  • Horses with a history of lymphangitis may benefit from supportive bandaging during rest periods and early cold hosing at the first sign of limb filling

Prognosis

For a first, acute episode treated promptly, the prognosis for recovery is generally good. However, lymphangitis can leave permanent damage to the lymphatic vessels and surrounding tissue, leading to chronic, recurring episodes of limb swelling (“chronic progressive lymphoedema”). Each subsequent episode tends to worsen the underlying lymphatic damage. Horses with chronic, recurrent lymphangitis require lifelong management — including regular exercise, bandaging support, and prompt treatment at the first sign of recurrence. Chronic ulcerative lymphangitis caused by Corynebacterium can be particularly difficult to resolve completely. Consult BEVA guidelines for evidence-based treatment protocols.

When to Call the Vet

  • A horse develops sudden, dramatic swelling of a limb, particularly if accompanied by fever, severe lameness, or systemic illness
  • Swelling of a limb has not improved within 24 hours of rest, cold hosing, and light exercise
  • You notice skin ulceration or discharge from nodules along the limb
  • A horse has had lymphangitis before and signs consistent with a new episode are developing
  • Any horse with limb swelling that you cannot clearly attribute to a benign cause (minor overnight filling in both hindlimbs after box rest) warrants veterinary assessment to rule out significant pathology

Frequently Asked Questions

Is lymphangitis the same as filled legs?

No. “Filled legs” or bilateral, soft, non-painful pitting oedema in both hindlimbs after box rest is a common, benign occurrence caused by gravity-dependent fluid accumulation and reduced lymphatic pumping from exercise. It typically resolves quickly with walking. Lymphangitis, by contrast, involves active inflammation of the lymphatic vessels, is typically unilateral, is associated with severe pain and heat, and often causes systemic signs including fever. These are distinct conditions requiring very different responses.

Will the leg return to normal after lymphangitis?

After a first episode, the limb often returns close to normal size with prompt treatment, though some permanent thickening of the lower limb may remain. Recurrent episodes progressively damage the lymphatic vessels, leading to a permanent increase in leg size that does not fully resolve between episodes. This is why rapid, aggressive treatment of the first episode and prevention of recurrence is important.

How long does treatment take?

A typical acute episode requires 7-14 days of systemic antibiotics, alongside daily cold therapy and exercise. The swelling may take several weeks to fully resolve. Chronic or recurrent cases may require longer courses and ongoing management with exercise, bandaging, and proactive monitoring. Your vet will advise on a treatment plan tailored to the severity and cause of the episode.

Can lymphangitis affect the horse’s ability to work?

In the short term, yes — the severe lameness associated with acute lymphangitis means the horse cannot be worked until the acute episode has resolved. Most horses with uncomplicated first episodes return to full work after recovery. However, horses with chronic recurrent lymphangitis may require ongoing management and may have limitations on the intensity of work, particularly after periods of box rest or in wet conditions that exacerbate limb swelling.