CPL, or chronic progressive lymphedema, is a condition in draft horses where the lymphatic system in the lower legs stops draining properly, causing progressive swelling, skin thickening, and tissue changes that worsen over time. There is no cure, but consistent daily management can slow the progression and keep affected horses comfortable for years.
How CPL Develops
The lymphatic system normally moves fluid out of tissue and back into circulation. In horses with CPL, this drainage fails in the lower legs. Fluid accumulates, and over time the skin and underlying tissue respond with scarring, thickening, and the formation of folds and nodules. Because draft breeds carry heavy feathering on their lower legs, the earliest signs are often hidden.
The first visible change, once feathering is clipped away, is a subtle loss of definition in the lower leg. Instead of a clearly defined cannon bone area and pastern, the leg takes on a cone shape with mild, even thickening. As the disease progresses, the skin develops hard nodules, deep folds, and crusty or ulcerated patches. In advanced stages the legs can become massively enlarged with heavy, fibrotic skin folds that crack and bleed. The condition typically affects both hind legs first, though all four legs can eventually be involved.
CPL never reverses on its own. Without management, secondary bacterial infections and parasitic mite infestations (particularly a mite called Chorioptes) settle into the damaged skin folds, creating a cycle of inflammation, infection, and further tissue damage that accelerates the disease.
Which Breeds Are Affected
CPL is overwhelmingly a draft horse problem. The Belgian draft horse is considered the breed at the center of the condition’s spread, since Belgians were used as foundation stock for draft breeds worldwide. Today, CPL has been documented in Shires, Clydesdales, Gypsy Cobs and Gypsy Vanners, Friesians, Percherons, Ardennes, Bretons, Comtois, and numerous German draft breeds including the Black Forest, South German, and Rhenish German, among others. Crossbreeds with draft ancestry can also develop the condition.
A study of 493 Rhenish German draught horses gives a sense of how widespread CPL is within a single breed. Only about 35% of horses scored completely clear. Roughly 20% had moderate signs, 24% had more advanced changes, and over 14% had severe or very severe disease. These numbers suggest that the majority of horses in susceptible populations carry some degree of CPL.
The Genetic Picture
CPL is considered a multifactorial disorder with a genetic component. Heritability estimates range from about 0.11 to 0.26, meaning genetics plays a real but partial role, with other factors like environment and management influencing whether and how severely a horse develops symptoms. Horses over three years old show higher heritability estimates, likely because the disease hasn’t yet become visible in younger animals.
Despite the strong suspicion of a hereditary basis, no specific genetic marker or mutation has been identified. There is currently no genetic test available for CPL. Breeders cannot screen for it the way they can for conditions like HYPP or GBED. This makes breeding decisions difficult, since a horse can appear healthy for years before clinical signs emerge.
How CPL Is Diagnosed
Diagnosis typically starts with a physical exam. A veterinarian clips the feathering and evaluates the leg contour, skin condition, and degree of swelling. Skin biopsies can show changes like swelling in the deeper skin layers, scarring, inflammation, and new blood vessel formation, but these findings aren’t unique to CPL and can show up in other skin conditions.
The most definitive diagnostic tool is nuclear lymphoscintigraphy, an imaging technique that tracks how lymph fluid moves through the leg. If the scan shows poor or absent lymphatic drainage, that confirms CPL and reveals the severity. This procedure has the advantage of being done while the horse is standing, making it practical for many equine veterinary facilities. Contrast-enhanced lymphangiography and CT scanning are also used in some cases to support the diagnosis.
Daily Management
Since CPL cannot be cured, the goal is slowing progression and preventing the secondary infections that make everything worse. This requires a daily commitment that becomes part of the horse’s routine.
Keeping the feathering clipped short is one of the most important steps. Long feathering traps moisture against the skin, creates a warm habitat for mites, and hides early changes that need attention. With the hair kept short, you can monitor the skin daily, keep it clean and dry, and catch problems early. Daily hoof cleaning and regular trimming of ergots and chestnuts also help maintain skin health around the lower leg.
Daily exercise is essential. Movement is what drives lymphatic flow in the legs, since the lymphatic system relies on muscle contractions rather than a pump like the heart. Horses that stand idle in stalls accumulate more fluid in the lower legs. Turnout, light work, or even daily hand-walking helps keep fluid moving.
Horses with CPL should be kept in dry environments. Moisture promotes bacterial growth and creates ideal conditions for mite reinfestations. Pesticide treatments in the barn may be necessary to control mite populations, and antiparasitic treatments help prevent Chorioptes mites from recolonizing the skin. Secondary bacterial infections are treated with antibiotics as they arise.
Specialized Therapies
Beyond daily care, two therapies borrowed from human lymphedema treatment can make a noticeable difference. Manual lymph drainage massage uses gentle, rhythmic pressure to encourage fluid movement through the lymphatic vessels. When done consistently, it can reduce swelling and improve tissue condition.
Compression bandaging is also very helpful for managing fluid buildup, but it carries real risks if done incorrectly. Improper wrapping on a horse’s lower leg can restrict blood flow or cause pressure sores. This technique should only be performed by professionals trained in equine compression therapy.
Together, daily management and specialized therapies form a package known as combined decongestive therapy. No single element works well in isolation. The combination of clipping, cleaning, exercise, mite control, massage, and compression gives affected horses the best chance at a comfortable life, even as the underlying condition continues its slow progression.
What to Expect Long Term
CPL is a lifelong condition that will progress regardless of treatment. The word “progressive” in the name is accurate. What good management does is slow that progression significantly and prevent the painful secondary complications, especially deep skin infections and severe mite infestations, that erode quality of life fastest.
Horses diagnosed early and managed consistently can remain functional and comfortable for many years. Those diagnosed late, or whose care lapses, tend to develop the severe skin folds, chronic infections, and lameness that make the condition debilitating. The daily time commitment is substantial, particularly for owners used to lower-maintenance breeds, but it is the single biggest factor in outcomes. Early detection matters, so if you own a draft breed or draft cross, clipping the feathering periodically to inspect the lower legs is a simple habit worth building.