Horses have tiny lymphatic vessels in their legs, without any valves preventing backflow. The flow of fluid up the leg is dependent on movement of the tissues near the lymphatic vessels. When horses are inactive, such as standing inside a stall for any extended period of time, this can cause the tissue fluid in the lower legs to accumulate. This accumulation of fluid results in mild swelling of the lower legs, referred to as 'stocking up'. Swelling usually starts at the coronet and slowly moves upward until reaching the fetlock. It is most common in the hindlegs, but can occur in all four legs. In all cases, the swelling is bilateral--meaning that the same amount of swelling should appear in both hindlegs or both frontlegs. There should be no heat present to the touch, a horse that is stocking up will feel normal temperature or slightly cooler than normal. The swelling should quickly resolve once the horse becomes active.