Question: My horse is usually turned out 24/7, but I've been leaving him in his stall during the day because of hot weather. When I bring him out of his stall in the evening, his hind legs are swollen from his coronary band to just above his fetlock. I've been told he is "stocking up." Why does this happen, and what can I do about it?
Answer: Stocking up is a very common problem caused primarily by stabling. In the wild, the average horse is on the move 20 hours a day, grazing, walking to water, fighting (or play fighting) and--when necessary--fleeing from predators. This nearly constant motion serves as an integral part of the circulatory system. Here's how:
The heart pumps blood containing oxygen and nutrients through the arteries to the arterioles (very small arteries) and microscopic capillaries, where the oxygen and nutrients "leak" across the walls into surrounding tissues. Any waste products and unused nutrients drain back into the lymphatic system, a network of vessels that act like the body's sewer system, filtering fluids through the lymph nodes and back to the veins and then the heart.
In most parts of the horse's body, the lymphatic system's job is literally an uphill battle. To push the fluids against the force of gravity, the system relies primarily on the pumping motions of the digital cushion in the hooves, and secondarily on the muscles, tendons, ligaments and joints in the legs. By staying consistently active throughout the day and night, therefore, a horse maintains a healthy equilibrium between fluids entering and exiting the body tissues.
When confined to a stall, though, a horse doesn't move as much, so the lymphatic system's pumping mechanism is drastically impaired. Fluid pumped into the tissues by the heart and arterial system isn't removed as efficiently, and gradually accumulates, much the way fluid swells your ankles when you sit on a plane for many hours. This "stocking up" is especially common in the lower parts of the horse's hind legs, which are farther from his heart than any other part of his body and most affected by gravity because the lymphatic vessels there are tiny and don't have valves to prevent backflow.
Several other factors can contribute to stocking up. Just as in humans, a horse's circulation diminishes with age. In rare cases, heart disease may be involved. And a horse will be more likely to stock up if he has a history of cellulitis or lymphangitis--even a single episode many years in the past. In both conditions, infection causes inflammation of the skin and subcutaneous tissues, which clogs the leg's lymph vessel "sewer system." Eventually, this leads to scarring of the lymph vessel walls, reducing their long-term elasticity and diminishing their function even more.
The good news: Stocking up may be unsightly, but it is generally harmless and painless. What can you do about it? First check to be sure your horse isn't dealing with a more acute condition, such as an infection or tendon, ligament or joint injury. If the swelling disappears after exercise or turnout, you can be pretty sure it was just the result of stocking up. If swelling remains, occurs only in one leg (stocking up is invariably bilateral), is painful or is accompanied by a fever, ask your veterinarian to investigate further.
Many horsemen like to use standing wraps to prevent stocking up, but bandaging can actually exacerbate the problem. It prevents air and sun from reaching the skin and concentrates sweat, opening the pores to dirt and bacteria and increasing the risk of infection. And bandaging also can create pressure rubs, which compromise circulation. Over time, the lymphatic system can become dependent on routine bandaging, so the next time you stable your horse without bandages, he'll stock up even more.
Similarly, most topical treatments (poultices, liniments, etc.) are counterproductive. By disrupting the natural balance of healthy bacteria on the skin, they make it more prone to infection.
The best solution to stocking up is to let Mother Nature take care of it. Turn out your horse and exercise him as much as possible. If you have a paddock with shade trees or a run-in shed, turn him out there on hot days instead of stabling him. If there's no outdoor shade available or it's too buggy to keep him pastured around the clock, stable him for just the hottest, buggiest hours of the day.
Dr. Steve Soule's areas of expertise include lameness diagnosis, surgery and performance problems. He's traveled extensively for the U.S. Equestrian Team and officiated at the 1996 Atlanta Olympic Games. He also has been a veterinary delegate or president of the veterinary commission at over 75 FEI dressage competitions, jumper shows, events and -endurance rides. His practice is based in Wellington, Fla., where he treats A-circuit hunters, jumpers and dressage horses.