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. [1]

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). [1]

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. [7]

These open wounds can exacerbate the condition, allowing more bacteria into the horse`s already compromised system.

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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. [12]

The most common bacteria types associated with lymphangitis in horses include:

  • Corynebacterium pseudotuberculosis
  • Staphylococcus aureus (staph infection)
  • Streptococcus
  • Escherichia coli [1][7]

Epizootic lymphangitis is another form of lymphangitis caused by a fungal infection from histoplasma farciminosum. [9]

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 Symptoms

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)
  • Fever
  • Lethargy
  • 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. [7]

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. [11]

Ulcerative Lymphangitis

Ulcerative lymphangitis (pigeon fever) is a rare but severe case of lymphangitis that affects more than just the lower limbs. [1]

This disease is caused by the introduction of Corynebacterium pseudotuberculosis or Staphylococcus aureus bacteria into the lymphatic system.

Ulcerative lymphangitis results in abscesses on the lower limbs and internal organs, as well as swelling and abscessing in the chest and neck. [1][8]

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. [1]

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. [3]

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. [4]

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

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. [6]

While stocking up is usually temporary and minor, if left unaddressed the swelling can worsen and damage the lymph vessels, potentially leading to lymphangitis. [2]

Cellulitis

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