It is quite probable that many people have never heard of chronic progressive lymphedema. However, if you have spent time with draft horses, chances are much more likely that you are familiar with the condition. This painful, debilitating disease has been identified in Shires, Clydesdales, and Belgians (especially those actually in Belgium). “Percherons, Suffolk Punches, Friesians, and other draft breeds without much feathering on the legs are not usually affected,” says Gregory L. Ferraro, DVM, director of the Center for Equine Health at the University of California, Davis. Progressive swelling and thickening of the skin on the lower legs characterizes the condition. Encrusted lesions develop underneath the draft’s beautiful feathers (long hairs at the fetlock), and clipping that hair is sometimes the only way to see them.

The clinical signs of lymphedema closely resemble chronic lymphedema or elephantiasis nostras verrucosa in humans. In these human conditions, the swelling is caused by a malfunctioning lymphatic system and a compromised immune system. It is believed that this might also be the cause of lymphedema in horses. However, to better understand the disease, it will be helpful to briefly review the lymphatic system.

The Lymphatic System

The lymphatic system is a one-way route for interstitial fluid (in the body’s tissues) to get to the cardiovascular system. Lymphatic capillaries are present in almost all organs, and they have large, water-filled channels that are permeable to all interstitial fluid constituents, including protein.

The lymphatic system functions to transport body fluids and protect against disease. Lymph, a protein-rich liquid derived from the interstitial fluid, is transported through the lymphatic system to the major vein returning blood to the heart, the vena cava. This process also returns fluid that leaks from capillaries back into the circulatory system