Understanding Lymphangitis

Lymphangitis is a painful bacterial infection of the lymphatic system that most commonly affects a horse's hind limb and requires prompt veterinary treatment to minimise the risk of permanent damage.

Understanding Lymphangitis

Lymphangitis is a painful and potentially serious condition that most commonly affects the hind limbs of horses. Although it can develop rapidly, early recognition and prompt veterinary treatment often lead to a good outcome.

Left untreated, however, severe cases can permanently damage the lymphatic system, leaving the horse with chronic swelling and an increased risk of future episodes.

Types of Lymphangitis

Three forms of lymphangitis are recognised:

• Sporadic lymphangitis – by far the most common form encountered in the UK.
• Ulcerative lymphangitis – a more severe form involving abscess formation and discharge through the skin.
• Epizootic lymphangitis – a contagious fungal disease that has not been reported in the UK for many decades.

This article focuses on sporadic lymphangitis, which is the form horse owners are most likely to encounter.

Understanding the Lymphatic System

The lymphatic system is one of the body's most important, yet often overlooked, defence mechanisms.

Its primary functions are to:
• Remove excess fluid from body tissues.
• Filter bacteria, viruses and other foreign material.
• Support the immune system.
• Return cleaned lymphatic fluid back into the bloodstream.

Unlike the circulatory system, the lymphatic system has no pump of its own. Instead, lymph fluid relies on muscle movement and changes in tissue pressure to keep it flowing.

Throughout the body are thousands of lymph nodes. These small, bean-shaped structures act as biological filters, slowing the flow of lymph so that bacteria, debris and other unwanted material can be removed before the fluid is returned to the circulation.

Why Horses Are More Susceptible

The horse's anatomy presents two particular challenges.

Firstly, horses possess far more lymph nodes than humans. While this provides an extensive filtering system, it also naturally slows the movement of lymphatic fluid as it passes through each node.

Secondly, horses have very little muscle below the knee and hock. Because lymph flow relies heavily on muscle contraction, fluid naturally tends to accumulate in the lower limbs, particularly during prolonged periods of standing.

This is why older horses, horses recovering from injury and those spending long periods stabled are more prone to lower limb swelling.

Stable Fill Is Not Lymphangitis

Many horses develop swollen lower legs after standing in a stable for several hours.

Commonly referred to as stable fill, this swelling occurs because lymphatic drainage temporarily slows during periods of inactivity. Once the horse begins walking or is turned out, normal muscle movement usually restores lymph flow and the swelling subsides.

Although the appearance can be alarming, stable fill is not lymphangitis.

What Causes Lymphangitis?

Lymphangitis is inflammation of the lymphatic vessels, most commonly associated with a bacterial infection.

The bacteria usually enter through a small cut, abrasion or other break in the skin—often so minor that it goes unnoticed.

As infection develops within the lymphatic system, drainage becomes impaired. The resulting inflammation and fluid accumulation can cause rapid and dramatic swelling of the affected limb.

Clinical Signs

• Sudden swelling of one hind limb.
• A limb that is noticeably hot and painful to touch.
• Severe lameness.
• A high body temperature, often between 40–41°C.
• Depression, lethargy or reluctance to move.

Although the hind limbs are most commonly affected, any horse showing these signs should be examined by a veterinary surgeon without delay.

Why Early Treatment Matters

Prompt veterinary treatment is essential.

Without appropriate treatment, inflammation can become increasingly severe and may progress to ulcerative lymphangitis, where multiple abscesses rupture through the skin, releasing pus, serum and lymphatic fluid.

Repeated or severe episodes can permanently damage the lymphatic system, leaving the horse with persistent limb enlargement and increasing the likelihood of future recurrence.

The sooner treatment begins, the better the long-term outlook.

Key Takeaways

• Lymphangitis is a serious infection and inflammation of the lymphatic system, most commonly affecting one hind limb.
• It usually develops after bacteria enter through a small wound or break in the skin.
• Stable fill and lymphangitis are different conditions and should not be confused.
• Sudden swelling, heat, severe lameness and a high temperature should always be treated as a veterinary emergency.
• Early diagnosis and prompt veterinary treatment offer the best chance of a full recovery and reduce the risk of permanent damage.

About the HØØF Knowledge Hub

The HØØF Knowledge Hub exists to provide horse owners with clear, practical and evidence-based information on hoof health, lower limb conditions and farriery.

Every horse is an individual, and no online article can replace professional assessment. If you have any concerns about your horse's health or soundness, always seek advice from your veterinary surgeon or registered farrier.

Article Information

Author: Paul Conroy BSc (Hons) AWCF
Organisation: HØØF Equine Hoof Care
Category: Lower Limb Health
Document Reference: HKH001
First Published: July 2026
Last Reviewed: July 2026

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