Lymphangitis, also known as big leg disease or stovepipe leg, is a condition in horses involving inflammation of the lymph vessels, most often in the lower limb. 
Lymphangitis presents as extreme swelling with rapid onset, resulting in pain in the lower leg, reluctance to bear weight, lethargy, lack of appetite, and sometimes fever.
This condition is caused by bacterial or fungal infection, usually following a wound to the leg. The infection can also result in very painful sores or lumps on the leg and cracking of high-motion skin areas (such as the fetlock). 
Seek veterinary care immediately if you suspect your horse has lymphangitis. If left unaddressed, the infection can spread to other organs and cause internal abscesses or sepsis, a potentially life-threatening condition.
Lymphangitis can be difficult to treat and often does not completely resolve. Proper management can keep an afflicted horse comfortable and reduce the risk of complications, but the horse may need to be retired from their athletic career.
Lymphangitis in Horses
Lymphangitis is caused by bacteria entering the lymphatic system, usually via a wound to the lower limb. Bacteria travel through abrasions into the deep layers of the skin, entering the lymphatic vessels.
After detecting an infection, the horse’s immune system transports infected lymph fluid from the leg to the lymph nodes. The lymph nodes are responsible for clearing infection from the fluid, but they can become infected themselves.
Infected lymph vessels become swollen, damaged or blocked, causing lymph fluid to pool in the limb. As fluid accumulates, the leg experiences progressive swelling.
The skin becomes taut and may crack, forming lesions (ulcers) that seep clear, yellowish lymph fluid. Crusty yellow flakes of dried lymph may form on the skin. 
These open wounds can exacerbate the condition, allowing more bacteria into the horse`s already compromised system.
Causes of Lymphangitis
Lymphangitis is caused by pathogens entering the horse’s body through a skin laceration (wound or abrasion).
It may develop following an injury, cut, puncture wound, insect bite, injection, or secondary to another skin condition such as mud fever. 
The most common bacteria types associated with lymphangitis in horses include:
- Corynebacterium pseudotuberculosis
- Staphylococcus aureus (staph infection)
- Escherichia coli 
Epizootic lymphangitis is another form of lymphangitis caused by a fungal infection from histoplasma farciminosum. 
These pathogenic agents thrive in wet, muddy conditions. Horses standing in mud for long periods or horses with damp legs are susceptible to lymphangitis because the skin’s natural oil barrier becomes compromised.
Lymphangitis typically affects a single hind limb at a time, resulting in swelling in the lower (distal) limb.
Symptom onset occurs rapidly in horses with lymphangitis. Some clinical signs of this condition include:
- Extreme swelling of the lower limb
- Heat in the limbs
- Pitting edema (a fingerprint remains in the skin when you press on the swollen area)
- Cracking or splitting of the skin
- Crusty yellow discharge that can scald the skin
- Skin that is extremely painful and hot to the touch
- Reluctance to bear weight or move the limb
- Inappetance (lack of appetite)
- Dark, wart-like growths that are painful and bleed profusely when peeled off
If your horse displays any of these signs, consult with your veterinarian to determine if your horse has lymphangitis or another related condition. 
If swelling continues unchecked, blood flow to the limb can be compromised enough to cause the hoof capsule to come off. The horse will require euthanasia. 
Ulcerative lymphangitis (pigeon fever) is a rare but severe case of lymphangitis that affects more than just the lower limbs. 
This disease is caused by the introduction of Corynebacterium pseudotuberculosis or Staphylococcus aureus bacteria into the lymphatic system.
The lower limbs become lumpy with small abscesses that open and drain puss-like fluid.
This infection can be fatal; 30 – 40% of horses that suffer from internal abscesses do not survive. 
The Equine Lymphatic System
The horse’s lymphatic system is similar to the circulatory system.
Whereas the circulatory system transports blood containing nutrients and oxygen to cells, the lymphatic system transports lymph fluid to carry waste products away from cells.
The lymphatic system is crucial for immune function, fluid balance and the filtration of water products from around tissues.
Lymph fluid travels through a system of lymph vessels to lymph nodes around the body. These vessels have one-way valves that prevent fluid from back-flowing down the legs due to gravity.
Lymph nodes contain white blood cells called lymphocytes, which function as part of the immune system. Lymphocytes detect and destroy dangerous pathogens, such as bacteria or viruses. 
Movement of Lymph Fluid
Your horse’s heart pumps blood through their circulatory system, but the lymphatic system does not have an active pump.
Instead, lymph fluid circulation depends on indirect mechanisms such as muscle contraction, movement of the limbs, and pulsation of the adjacent blood vessels.
Horses that stand for long periods without adequately moving their limbs can experience pooling of lymph fluid in their legs. This is temporary and usually resolves after exercise.
However, in cases of lymphangitis, the lymph vessess become inflamed and lose their ability to adequately transport lymph fluid. Continued pooling within the limbs can cause enough damage to the lymphatic vessels to block fluid drainage even with movement.
Damaged lymph vessels often do not heal well, making lymphangitis a disease with a poor prognosis. 
Stocking Up vs. Cellulitis vs. Lymphangitis
Many horse owners confuse stocking up and cellulitis with lymphangitis.
All three conditions have similar presentations and are associated with swelling to the lower limbs, but only lymphangitis is caused by damage to the lymphatic system.
Stocking up, also known as stagnation edema, refers to a buildup of lymphatic fluid in the horse’s lower limbs due to a lack of movement.
Stocking up is a direct result of sustained inactivity; once the horse starts moving the symptoms resolve. This temporary swelling does not require antibiotic treatment and is not usually painful to the horse.
Pressure or standing bandages are used to reduce swelling when physical activity is not possible, but these simply move the swelling up the leg. 
While stocking up is usually temporary and minor, if left unaddressed the swelling can worsen and damage the lymph vessels, potentially leading to lymphangitis. 
Cellulitis involves an infection of the horse’s subcutaneous soft tissues (tissues under the skin).
It occurs when bacteria, commonly of the Streptococcus family, enter into the deep layers of the skin, damaging blood vessels and allowing leakage of lymph fluid into the area.
Cellulitis presents as sudden swelling of the horse’s limb. While this infection can occur anywhere on the horse’s body, it is most often seen in the lower legs.
Horses with cellulitis experience extreme pain in the affected area and are often very lame, sometimes refusing to weight-bear. In addition, horses may have a fever and may be reluctant to eat.
In horses with cellulitis, the lymphatic vessels are not usually damaged. Once the infection is treated with anti-inflammatories and antibiotics, the swelling and discomfort usually resolve.
If left untreated, cellulitis can lead to permanent damage to the lymph vessels, resulting in lymphangitis. Cellulitis can also lead to sepsis, a deadly systemic infection. 
Lymphangitis is the most serious of the three conditions that commonly cause leg swelling in horses.
Like cellulitis, lymphangitis usually results from a bacterial infection that causes swelling and impairs the flow of lymph fluid through the lymphatic system.
Unlike cellulitis, the main feature of lymphangitis is inflammation and damage to the lymphatic vessels and not the subcutaneous soft tissues.
Like cellulitis, lymphangitis is extremely painful for the horse. Lymph fluid accumulates in the lower limb, causing severe swelling and stretching of the skin and tissues within the leg.
Unlike cellulitis, lymphangitis is difficult to treat and often has long-term consequences. Once damaged, lymphatic vessels can develop scar tissue that impedes lymph flow.
Even after the bacterial infection is treated, the horse may experience recurrent swelling and pain in the limbs. 
In some horses, lymphangitis repeatedly occurs once the initial infection has resolved. If your horse experience repeated episodes of lymphangitis, your veterinarian may diagnose sporadic lymphangitis. 
Your veterinarian will diagnose lymphangitis upon observation of clinical signs and ruling out other causes of leg swelling.
Treatment of a horse with lymphangitis centers on two goals:
- Control the pain and inflammation
- Treat the bacterial infection
Lymphangitis has a guarded prognosis, which means the outcome is uncertain and some horses experience on-going complications.
Control Pain and Inflammation
Horses with lymphangitis experience a lot of pain and often do not want to move. This makes it difficult to resolve the swelling as lymph drainage from the legs relies on movement.
To encourage the horse to move, your veterinarian will administer medications to alleviate pain and inflammation in the limb.
Your veterinarian may prescribe non-steroidal anti-inflammatory medications (NSAIDs), such as phenylbutazone (Bute) or flunixin meglumine (Banamine), to make the horse more comfortable.
Cold hosing of the limb may also provide some relief, so long as the leg is thoroughly dried after water application. A damp leg will only encourage bacteria to propagate and worsen the infection.
Your veterinarian may also administer intravenous dimethyl sulfoxide (DMSO) or corticosteroids to reduce inflammation. Some veterinarians may treat with diuretics to draw moisture from the horse’s tissues and increase urine output. 
If abscesses or cysts are present under the skin, your veterinarian may lance and drain them. Draining abscesses will relieve pressure and improve your horse’s pain.
Wrapping with Bandages
It may be tempting to apply standing or pressure bandages to your horse’s leg, but this may cause more harm than good. Horses in the acute phase of lymphangitis will continue swelling above the pressure bandage, potentially restricting blood flow to the lower limb.
Promoting Lymph Flow
After addressing the horse’s pain, encourage them to move around as much as possible to pump lymph fluid up from the limb. Hand walking, turnout, and gentle exercise can help reduce swelling.
Some owners recommend lymphatic massage for the lower limb, but this may be difficult if the leg is painful to the touch. Research is not available to evaluate the efficacy of massage therapy for lymphangitis in horses.
Treating Bacterial Infection
Your veterinarian will recommend the best course of antibiotic medications to treat the bacterial infection causing lymphangitis in your horse.
Your veterinarian may take a bacterial culture from the horse`s leg by swabbing any open sores in the skin and submitting the sample to a laboratory for identification.
If the swollen limb has open wounds, your veterinarian may suggest cleaning the leg with an antiseptic solution to eliminate bacteria. Provide the horse with pain relief and/or sedation before cleaning, as even light touch to the area can be incredibly painful. 
Lymphangitis is a serious condition that rarely goes away completely. The horse’s lymph vessels may be permanently damaged and the horse may experience ongoing swelling.
- Exercise the horse daily
- Avoid unnecessary stall rest
- Treat all leg wounds, no matter how small, by thoroughly cleaning the region and applying antibiotic ointment
- Call your veterinarian immediately if you notice any swelling or lameness
- Stable the horse with magnetic or ceramic wraps to encourage lymphatic movement
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