Why Is My Horse's Leg Swollen?

Filled legs (stocking up)

"Filled legs", "stocking up" and "humour" are everyday names for oedema. This is fluid that collects under the skin and settles in the lowest part of the body.

The hind legs are usually more swollen than the fronts, and the swelling is similar in each pair. It is not uncommon in autumn and winter, when horses spend more time standing in the stable.

A 2006 Horse & Hound Vet Clinic article describes this swelling as cold, soft and painless. It says the swelling goes down with gentle exercise or turnout.

Why legs fill

When a horse stands still, circulation becomes sluggish and fluid leaks out.

Your Horse lists long periods of standing still, too much protein, overfeeding or obesity, and too much moisture as possible causes. A 2016 Horse & Rider answer says there are many anecdotal reports of legs filling on new pasture or with certain hay, but no scientific evidence that this is a cause for concern.

Windgalls

Windgalls are leftover inflammation from old tendon or ligament injuries. They sit at the back of the leg at or just above the fetlock, and are usually painless.

Injury to a tendon, ligament or joint

Sprains and strains often cause inflammation, pain, swelling and lameness. Your Horse says these need immediate veterinary attention.

Lameness, heat and swelling are signs of a tendon or ligament injury, according to World Horse Welfare. Our guide to Tendon Injuries in Horses covers this in more detail.

Hoof abscess

A hoof abscess can make the leg fill because of inflammation in the foot. Sudden, severe lameness is typical. Swelling can develop around the coronary band or pastern, and sometimes it extends up the leg.

See our guide to Hoof Abscess in Horses for more.

Mud fever and skin problems

Mud fever can cause heat, pain and swelling in the lower limb, and the horse may not tolerate the area being touched. The British Horse Society says infections can develop under the scabs, and the leg may swell in severe cases.

If left untreated, mud fever can lead to cellulitis and even lymphangitis. These conditions can often affect one leg at a time. Read more in Mud Fever in Horses.

Cellulitis

Cellulitis is a bacterial infection of the deeper layers of the skin. In horses it commonly affects one hind leg. It typically starts with sudden swelling that feels warm and painful, and your vet needs to see the horse.

The way in can be a tiny puncture wound that is hard to find.

Lymphangitis

Lymphangitis is inflammation of the lymph vessels. It usually affects a hind leg, which becomes hot, very painful and extremely swollen, often at least double the size of the other leg.

The horse is often unwilling to move and generally has a raised temperature. It may sweat and go off its food, and yellow fluid may ooze through the skin.

Your Horse says to contact your vet immediately if you notice these signs. The leg may never return to its original size, and a horse that has had lymphangitis once is likely to be prone to it happening again.

Whole-body causes

If all four legs fill at once and the horse seems unwell, the cause may lie elsewhere in the body. Sources mention heart problems, low blood protein and allergic reactions. Your vet needs to investigate these.

A 2006 Horse & Hound article describes a condition called purpura haemorrhagica, believed to be an allergic reaction, which can follow strangles or equine flu. Swelling of all four legs, with fever or dullness, calls for a vet at once.

Other local causes

Bruising, insect bites, scrapes, wounds, allergic reactions and arthritis can also cause heat, swelling or pain. Swelling in a single limb usually points to a local problem.