Stocked up or stocking up is a phrase used to describe a horse's legs when they swell up, usually below the knees. Many people will notice that after a night spent in a stall, a horse's legs may appear slightly, or sometimes dramatically swollen in the morning. Once the horse is turned out and allowed to move around in its pasture, the swelling disappears.
Stocking up differs from swelling due to injury in that the horse is unlikely to be lame, and the swelling will be generalized, not in any specific location. Usually, the fronts or backs or all four legs will be swollen, rather than one leg—which could indicate an injury. The swelling is normally below the knees and hocks. The swelling will also subside as soon as the horse moves around.
Designed for Motion
Horses are designed to move almost constantly. Their hearts pump blood throughout their bodies, and of course, to their extremities. The digital cushion in the hooves and the soft tissues such as the leg muscles and tendons, help circulate the blood as the horse moves its legs. As the blood circulates it carries nutrients and oxygen to ever smaller blood vessels, the smallest being capillaries too small to see with the naked eye.
Through the walls of these minute capillaries, the nutrients and oxygen pass into the surrounding tissue. The unused nutrients and any waste are then drained into the lymphatic system, where ideally, they are filtered through the lymph nodes. The blood filters back into the veins, to be circulated back to the heart where, of course, it repeats the process.
Key to this all is that the pumping action of the digital cushion and to a lesser extent, the muscles, tendons, ligaments, and joints in the legs aid in the circulating and blood cleansing process. For this to happen efficiently, the horse must be moving. When a horse is confined to a stall, where it cannot move freely, this process may be hampered.
Since the blood and waste must be pumped up the legs, back to the heart, some of it can pool if the horse is not moving. This pooling results in the swelling that we call 'stocking up'. It is, in fact, edema, and some horses seem to be more prone to it than others. Stocking up may be more likely in older horses, whose circulatory system isn't as strong as it once was. Some horses may have undiagnosed heart problems or may have had health problems that impair the lymphatic system in their legs.
If your horse is prone to stocking up, the best remedy is to allow it freedom in a paddock or pasture where it can be encouraged to move by placing water, feed, and shelter in different places. The more your horse moves, even at a walk, the better. When the weather is bad, keep your horse stabled during only the worst part of the day.
If it's impossible to turn the horse out, cold hosing is the next-best option. This may come with problems of its own; effective cold hosing takes time and leaves your horse's legs damp—which might not be a good idea in some conditions. You may also try hand walking as much as possible, even if it is up and down the alley of the barn. Gentle riding can also help.
Some horses seem to respond to certain feeds, so take a look at any changes in the grains or concentrates your horse is getting. Occasionally, swelling may be related to allergies.
Bandaging, poultices, and liniments may help in the short term but may cause problems as well. Improperly applied standing bandages can damage the horse's legs, and topical remedies may cause skin problems. Bandaging may actually make the horse more prone to stocking up.