Let’s talk about a disease called cutaneous lymphangitis. Dr. Alan Loynachan from the University of Kentucky says that the lymphatic system is an important part of the cardiovascular system; it consists of lymphatic vessels, lymph nodes, tonsils, spleen and the thymus. Although most of you are familiar with lymph nodes, tonsils and spleens, you may not realize there are small lymph vessels that carry lymph fluid that is formed when fluid loss occurs in tiny capillary beds during normal nutrient exchange.  This lymph fluid is carried to lymph nodes to be filtered and to detect microorganisms, toxins and foreign material.  After filtration, the lymph is then carried to large veins that return it to the heart. Lymphatic disease can occur when lymph vessels become inflamed, leaky, or blocked.  It’s why your lymph nodes swell up under your throat when you get a sore throat. 

Cutaneous lymphangitis in horses is inflammation of these lymph vessels of the horse’s skin, usually below the hock, that leads to a leg swelling commonly called big leg.  Generally, these horses not only have a swollen leg, but also have nodules on the skin that can abscess and cause lameness.  The disease is generally considered to be caused by keeping the horse in a dirty area, but I think many cases occur after biting flies transmit organisms.  It can also occur after lacerations on the lower legs get bacterial or fungal contamination.  Most horses respond to antibiotics, exercise, cold hosing of the legs, and topical treatment of the skin.  However, delayed treatment can lead to scar tissue and permanent swelling, so if your horse has a swollen leg, do not wait to call your vet.