All about lymphangitis in horses 

Firstly, what is the lymphatic system? 

To understand the processes behind lymphangitis, it first helps to understand what exactly the lymphatic system is. The lymphatic system is a network of vessels, lymph nodes and organs that form part of the immune system. Parts of the body, including the thymus, bone marrow, spleen and tonsils, produce and process specialised white blood cells that work to fight infection. Lymphatic fluid is transported around the body in vessels, not dissimilar to veins, passing through lymph nodes. The lymph nodes act as filters, removing damaged cells, cancerous cells and foreign pathogens. It is here, that the specialised white blood cells are added to the lymph fluid, such as lymphocytes and macrophages, created to further destroy potentially harmful cells.  

Lymph fluid in the extremities relies heavily on movement to be returned back into the body. This is very important in horses, as their limbs are relatively long with relatively little muscle to assist lymph movement. Every step a horse makes helps pump lymph fluid back upwards against gravity. If this is damaged in some way, lymph fluid accumulates in the tissues, leading to swelling.  

So, what is lymphangitis? 

Put simply, lymphangitis is inflammation of the lymphatic vessels. In horses, it most commonly affects one limb, usually a hindlimb, and often develops suddenly. The affected leg can become markedly swollen, hot, painful and firm to the touch. One common marker is “pitting oedema”, where a thumbprint in the swollen limb stays indented for some time – showing that the lymph vessels aren’t carrying away the fluid properly. In more severe cases, the horse may be reluctant to bear weight on the limb and can even show signs of systemic illness, such as fever, lethargy and reduced appetite.  

Lymphangitis is not a single condition, but rather a clinical syndrome with several possible underlying causes. Identifying and addressing these causes is essential for effective treatment and prevention of recurrence. 

Causes of lymphangitis in horses 

The most common cause of lymphangitis in horses is bacterial infection. Bacteria can enter the body through even very small breaks in the skin, such as cuts, abrasions, insect bites, mud fever lesions or cracked heels. Once bacteria gain access, they can spread through the lymphatic vessels triggering inflammation and swelling. 

Commonly involved bacteria include Streptococcus species and Staphylococcus species, although mixed infections are also possible. In some cases, the original wound may be so small that it goes unnoticed. 

Other contributing or predisposing factors include: 

• Prolonged stabling or reduced movement 

• Poor skin condition or chronic dermatitis 

• Previous episodes of lymphangitis causing lymphatic damage 

• Chronic limb swelling or scarring 

• Obesity 

In some horses, lymphangitis can develop without an obvious infectious trigger. These cases may be related to underlying lymphatic dysfunction or chronic inflammatory conditions. 

Clinical signs of lymphangitis 

Lymphangitis often develops quickly, sometimes within hours. Owners may notice: 

• Sudden, marked swelling of one leg, often from the hoof up to the hock or stifle. 

• Heat and pain in the affected limb 

• Lameness, ranging from mild stiffness to non-weight bearing 

• Fever 

• Lethargy or depression 

• Reduced appetite 

In the more severe cases, the skin may weep fluid or develop firm nodules. Over time, repeated episodes can lead to thickened, fibrotic skin that feels hard, rather than soft and pitting. 

Any horse showing sudden, painful limb swelling should be examined by a vet as soon as possible, as early treatment significantly improves outcomes. 

Diagnosis 

Diagnosis is primarily based on clinical presentation and history. The dramatic onset of unilateral limb swelling, combined with pain with or without systemic signs, is often characteristic. 

You vet will perform a full clinical examination and may recommend additional tests depending on the severity and recurrence of the condition. These may include, but are not limited to: 

• Blood tests to assess inflammation and the presence of infection 

• Ultrasonography of the limb to evaluate the soft tissues and lymphatics 

• Sampling any wounds or discharge present for bacterial culture 

It is also important to rule out other causes of acute limb swelling, such as cellulitis, thrombosis, fractures or severe joint/tendon injury or infection. 

Treatment 

Treatment of lymphangitis aims to control infection, reduce inflammation and swelling, relieve pain and support lymphatic drainage. Early and aggressive treatment is essential. 

Antibiotics 

If bacterial infection is suspected or confirmed, antibiotics are a cornerstone of treatment. The choice of antibiotic and duration of therapy will depend on the severity of the case and the horse’s response to treatment. It is essential that antibiotics are given exactly as prescribed, for their full instructed course. 

Anti-inflammatory medication 

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to reduce pain, inflammation and fever. These medications help improve comfort and encourage the horse to move, which in turn supports lymphatic drainage. 

Controlled exercise 

Once the horse is comfortable, controlled exercise is one of the most important aspects of recovery. Movement helps the lymphatic system function effectively. Hand walking is often recommended initially, gradually increasing as swelling improves and pain decreases. 

Cold therapy and supportive care 

Cold hosing or ice therapy may help reduce heat and swelling in the acute phase. The limb should be kept clean and any wounds carefully managed. Stable bandaging may be recommended in some cases, but it must be applied correctly, as inappropriate bandaging can worsen swelling or cause pressure damage. 

Addressing underlying causes 

Identifying and managing predisposing factors is crucial, particularly in horses with recurrent lymphangitis. This may involve improving skin care, managing mud fever, increasing turnout and exercise, or addressing weight issues. 

Prognosis and recurrence 

Many horses recover well from an isolated episode of lymphangitis, especially if treated promptly. However, repeated episodes can damage the lymphatic vessels, leading to chronic limb swelling and an increased risk of future flare ups.  

Horses with recurrent lymphangitis often require long term management strategies rather than on-off treatments. Owner vigilance and early veterinary intervention at the first sign of swelling can make a significant difference.  

Chronic progressive lymphoedema (CPL) 

CPL is a distinct condition that deserves special mention. It is most commonly seen in heavy horses, such as Shires, Clydesdales and some cob types. It is a lifelong, progressive disorder of the lymphatic system rather than an acute infection, as described above. It is characterised by progressive failure of lymphatic drainage of the lower limbs. Over time, this leads to persistent swelling, thickening of the skin, formation of skin folds and development of secondary skin infections. Unlike acute lymphangitis, CPL is not primarily caused by bacteria, although secondary infections are common and can exacerbate the condition. The exact cause is not fully understood, but there is a strong genetic component. The condition is thought to involve abnormalities in the structure and function of lymphatic vessels. 

Clinical signs of CPL 

Early signs of CPL can be subtle and may include mild, persistent swelling around the pastern or fetlock. As the condition progresses, owners may notice: 

• Increasing limb swelling that does not fully resolve with exercise 

• Thickened, folded skin, particularly around the heels 

• Development of nodules or plaques 

• Chronic dermatitis and recurrent infections 

• Reduced mobility and discomfort 

Management of CPL 

Unfortunately, there is currently no cure for CPL, but careful management can significantly improve comfort and slow progression. Key aspects include: 

• Strict skin hygiene to reduce infection risk 

• Regular, appropriate exercise to support lymphatic flow 

• Weight management 

• Prompt treatment of any secondary infections 

• Carefully clipping and monitoring of feathered limbs 

Owners of horses with CPL should work closely with their vet to develop an individualised long term management plan. Early recognition and proactive care can make a meaningful difference to quality of life. 

Prevention of lymphangitis 

Whilst not all cases can be prevented, good management can reduce the risk: 

• Inspect legs daily for cuts, abrasions and signs of dermatitis. 

• Treat even small wounds promptly. 

• Manage mud fever and skin conditions effectively. 

• Encourage regular movement and avoid prolonged stabling where possible and appropriate.  

• Maintain a healthy body condition.  

Conclusion 

Lymphangitis in horses is a serious but often manageable condition when recognised and treated promptly. Understanding the role of the lymphatic system, recognising early warning signs and seeking veterinary advice without delay are crucial steps in protecting your horse’s health. For horses with chronic or recurrent problems, including those affected by chronic progressive lymphoedema long term management and close collaboration with a vet are essential. With informed care and attention, many horses with lymphatic disorders can continue to lead comfortable and active live.