Chronic Progressive Lymphedema (CPL) is a condition that describes impaired lymph flow in the lower legs. Primarily observed in draft horse breeds, CPL causes swelling and skin inflammation on affected legs. [1]

Horses with the condition are also at risk of lesions and secondary bacterial and parasitic infections developing on their legs because of poor lymph flow.

A veterinarian can typically diagnose CPL based on a clinical examination. There is no cure for CPL. However, intensive management strategies can slow the progression of the disease and improve the quality of life of affected horses.

CPL was recognized in 2003, although skin lesions associated with the condition were initially reported in the early 20th century. [1] CPL is believed to be caused by a combination of genetic and environmental factors.

What is Chronic Progressive Lymphedema?

The lymphatics are a system of vessels that lie in close proximity to the capillaries of the circulatory system. Any fluid or immune cells present in the tissue that are not taken up by the capillaries are picked up and circulated by the lymphatic vessels.

Lymphatic vessels move lymphatic fluid (also referred to as “the lymph”) through the body by contraction of smooth muscle. The vessels contain a series of one-way valves that prevent backflow and drain into the subclavian vein, which is a low pressure blood vessel located under the clavicle.

CPL is a chronic disease of the lymphatic system where lymphatic fluid accumulates in the lower legs of affected horses. [2]

CPL is a debilitating condition that causes secondary recurrent bacterial and parasitic infections due to poor lymphatic drainage and blood circulation. [2]

Recurrent infections promote the development of skin lesions that can extend up the leg to the knees or hocks. These infections typically increase the amount of lymphedema in the affected legs. [2]

Decreased lymph flow in the legs of horses with CPL may initially go unnoticed if heavy hair (feathering) is present on the legs. The tissue damage caused by CPL is progressive and can result in lameness, severe disability, disfigurement, and potentially premature death. [2]

Chronic progressive lymphedema differs from chronic pastern dermatitis, a condition that occurs due to primary infection with microorganisms.

Treatments of skin infections do not resolve the underlying lymphedema associated with CPL.

Lymphatic System Dysfunction and CPL

The role of the equine lymphatic system is to maintain fluid balance in the tissues, support immune function in the skin, and remove cellular waste products.

Protein-rich lymph fluid circulates throughout the body through lymph vessels and lymph nodes.

Elastin, an extracellular matrix protein, is necessary to move lymph fluid throughout the body. Abnormal elastin metabolism and impaired elastin quality in the skin are believed to be associated with CPL. [2]

If lymph flow is compromised, oxygen supply to tissues decreases and metabolic waste products accumulate within the body. Poor lymph flow (lymph stasis) impairs the skin’s immune response to pathogens and jeopardizes the integrity of the skin barrier.

In advanced cases of CPL, there may be complete lymph stasis due to lymphatic dysfunction, lymph vessel dilatation, and the formation of excess fibrous connective tissue (fibrosis). [2] CPL occurs in the lower legs because there are no muscles in the lower leg of the horse. In other areas of the body, the contraction of skeletal muscle helps move lymph.

Prevalence of CPL

Horses that develop CPL typically don’t show detectible signs of the disease before the age of two. [2]

CPL affects breeds including: [3]

  • Belgian draft horses
  • German draft horses
  • Shires
  • Clydesdales
  • Gypsy Vanners
  • English Cobs
  • Friesians
  • Percherons

The number of horses affected by CPL is unknown. However, a study of 161 Belgian draft horses found that 82% had CPL. [4]

Another study involving 912 horses of six different breeds of German draft horses older than 2.5 years determined a prevalence of CPL ranging from 47.5 to 96.1%. [4]

Intro to Equine Nutrition
Gain a deeper understanding of your horse's nutrition needs. This free introductory course provides a foundation for horse owners to learn how to balance your horse's diet.
Enroll Now
Introduction to Equine Nutrition Course Mad Barn Academy

Signs of CPL

The severity of CPL correlates with how severely lymphatic clearance is delayed. [1] Early signs of CPL include:

  • Swelling in the lower legs
  • Soft pitting edema

Advanced signs of CPL include:

  • Firm swelling in the legs
  • Folds in the skin due to swelling and tissue damage
  • Lesions (ulcers)
  • Fibrosis that results in nodule formation
  • Poor hoof growth
  • Thrush
  • Scaling skin
  • Granulation tissue
  • Discharge of exudate (pus) due to secondary bacterial overgrowth from the crevices of skin folds
  • Loss of shape of the lower leg
  • Skin folds on the neck and the trunk
  • Impaired movement due to nodule development and skin folds on the limbs

Secondary Infections

Horses with CPL are prone to the following types of recurring infections due to reduced lymph flow which disrupts the normal barrier function of the skin.

Bacterial Infections:

Skin infections in horses with CPL may involve bacteria including various species of Staphylococcus and Dermatophilus congolensis. [2] Heavy feathering traps moisture and bacteria that propagate infection.

Parasitic Infections:

Chorioptes bovis, a type of skin mite that causes chorioptic mange, is common in horses with CPL. [2]

Feathered horses with CPL are prone to overproducing keratin (hyperker