Horse Illustrated Magazine

There’s no doubt a horse with swollen legs can be worrying. However, passive fluid accumulation in the lower limbs — commonly called stocking up — is a relatively common condition in stalled horses that is not typically a cause for alarm. Here’s what you need to know about stocking up, along with a few other causes of swollen legs, and how to handle the condition.

The Lymphatic System

Fluid accumulation in the lower limbs (the medical term is “dependent edema”) is a function of physics and the lymphatic system, an often-overlooked branch of the circulatory and immune systems. As blood is pumped by the heart throughout the body, it delivers oxygen and nutrients. When blood reaches the tiny capillaries, these components diffuse out into the surrounding tissues, nourishing the body.

Inevitably, some metabolic waste is created, which results in what’s called lymph fluid. This fluid is then passively collected into the surrounding lymph vessels. In a way, the lymphatic system is like a sewer system where waste materials collect from around the body.

An important difference between the circulatory and lymphatic systems is the lymphatic system isn’t directly connected to the heart; it lacks a pump. Lymph, the fluid that flows through the system, relies on the extending and flexing of ligaments and tendons when the animal walks to squeeze and push it from the delicate lymph vessels to lymph nodes to veins and ultimately back to the heart. The digital cushion in the hoof also plays an important role in moving lymph back up the leg.

When you appreciate the role of the lymphatic system, it’s now easy to understand the primary cause of stocking up in horses, which is lack of movement. Stocking up is almost always seen in horses that have been stalled. When a horse doesn’t move enough, he can’t help his lymphatic system push fluid, not only from the more distant parts of his body (relative to his heart) but also opposite gravity.

When the lymph system can’t move enough fluid back to the heart in a timely manner, it begins to accumulate. Over the course of many hours (commonly overnight), this causes the legs to “fill” and can make the typically slender lower limb get fat and feel firm. The same thing happens to humans; swollen ankles after a long flight are a typical example of human stocking up.

Confirming Everything is OK

But how can you be sure a horse’s swollen legs are due to the benign nature of a lazy lymph system, and not something more sinister? Paying close attention to your horse will provide answers.

◆ First, stocking up is a bilateral condition, meaning stocking up occurs in both hind legs, but it’s not uncommon to see it in both front legs as well—and sometimes in all four.

◆ Second, a stocked-up horse will behave normally. He should not appear lethargic, unwilling to move, lame, or otherwise seem sick or painful.

◆ Third, the legs should not be hot to the touch. They will also be uniform in size, so compare each swollen leg to the others.

◆ Fourth, consider the horse’s history: Has he had this condition before? Has he been in a stall for a lengthy period? When was the last time he was out in the field or ridden?

Once you’ve determined your horse has fat legs but is feeling good, the tried-and-true test (and cure) to confirm is movement. Tack up your horse and go for a ride, or turn him out so he can stretch and move at liberty, then re-evaluate. The swelling should dissipate, confirming the fluid accumulation was due to inactivity.

Other Reasons for Swelling

In rarer instances, swollen legs can be a clinical sign of something much more serious than a lack of movement. Heart failure and liver failure are two conditions that are thankfully uncommon in horses, but when either occurs, it is typically severe, incurable, and can lead to fluid buildup in all four legs, along with a host of other clinical signs, which should prompt a call to your veterinarian.

Alternatively, if just one leg is swollen, this is a major clue something more serious is going on. Soft tissue damage, such as an acutely bowed tendon, can result in a swollen lower limb. So can many other types of musculoskeletal trauma, such as a fracture or bruising from a kick. The most obvious difference between these clinical presentations and stocking up, however, is the fact that the horse will likely be acutely lame when trauma is the cause.

Another cause of unilateral acute limb swelling is cellulitis. This is a bacterial infection under the skin, usually due to a small cut or scrape or a more chronic condition that weakens the integrity of the skin, like mud fever or scratches. If certain types of bacteria invade the soft connective tissue under the skin, they proliferate, resulting in an acutely swollen limb and a very lame horse.

Horses with cellulitis have a leg that is hot to the touch and may be oozing serum. Depending on the extent of the infection, the horse may have a fever, be lethargic, and not want to eat. This condition can spread to the local lymph vessels. When this happens, it is called lymphangitis, and is managed the same way as cellulitis. Quick treatment with aggressive antibiotics is required, so if you suspect cellulitis, have your veterinarian out as quickly as possible.

Vasculitis is another cause for acute swelling in the limbs. The medical term for the inflammation of blood vessels, vasculitis is often viral in origin. Any horse with swollen limbs and a fever should be evaluated promptly by a veterinarian.

Horses Prone to Stocking Up

Some horses seem to be more prone to stocking up than others. Older horses in general tend to stock up frequently. This is thought to occur because their lymphatic system isn’t as effective as it used to be, leading to more fluid accumulation. This may also be a function of an animal that is reluctant to move due to osteoarthritis or other chronic conditions.

Dehydrated horses also tend to stock up more easily. This is something to keep in mind after a long, hard ride or competition or when it’s extremely hot outside. Horses that have had cellulitis/lymphangitis in the past may also stock up more frequently in the previously infected leg if there was significant damage to the lymph vessels at the time of the infection.

Prevention

At face value, the prevention of stocking up is simple: keep the horse outside as much as possible. However, many horse owners don’t have adequate pasture access or have other restrictions that preclude full turnout, and that’s OK. It’s important to note that a truly stocked-up horse is not in pain, sick, or injured. Swollen legs in this instance won’t affect his well-being or athletic pursuits.

Some prefer to use standing wraps on horses to prevent stocking up. The use of wraps should be evaluated based on an individual horse’s environment, use, health, and your ability and expertise in applying them.

One issue with standing wraps is cleanliness: sweat, dirt, and debris can easily turn these wraps into bacterial breeding grounds, setting the horse up for chronic skin conditions. Wraps that are applied too tightly may further impede circulation and the flow of lymph, and over time, they may be counterproductive in preventing swelling.

Similarly, topical products such as poultices or liniments shouldn’t be relied upon for long-term management since overuse may also negatively impact the health of the thin skin on the horse’s legs. The simplest method to reduce stocking up is to increase your horse’s time out of the stall.

Once correctly identified, stocking up in your horse can go from a worry to no big deal. With a little understanding and observation, this fluid accumulation shouldn’t be cause for alarm.

This article about stocking up in horses appeared in the April 2022 issue of Horse Illustrated magazine. Click here to subscribe!