Stagnation edema, also known as stocking up, is a common cause of leg swelling in stabled horses. It occurs due to impaired circulation from periods of reduced activity.

This short-lasting form of edema typically affects both hind limbs and causes swelling from the coronary band up to the hock. Occasionally, it occurs in the forelegs as well. Stocking up is also called distal limb edema because it affects to lower portion of the limbs.

Another term for stocking up is pitting edema. This is because when pressure is applied to the area, a pit or indentation will remain temporarily.

Stocking up results from the pooling of lymph, a clear fluid that circulates in the lymphatic vessels. Sometimes this circulation is compromised allowing fluid to accumulate. This typically occurs if blood flow and lymphatic drainage are impaired.

Though stocking up may look alarming, it is typically not serious and resolves quickly once the horse begins moving again. However, in some cases of chronic stocking up, the swelling could be a symptom of a larger problem.

Many other causes of lower leg swelling may appear similar to stocking up but indicate a more serious condition. Being able to differentiate between stocking up and other conditions is important for horse owners.

Understanding the Horse’s Lymphatic System

To understand why horses stock up, it’s important first to learn how their lymphatic system functions.

When blood flows from the arteries to the capillary beds in tissues, some of the fluid escapes the blood vessels. Most of this is resorbed into the veins, however some remains outside the blood vessels. This remaining fluid enters the lymphatic vessels that run alongside blood vessels.

The main role of the lymphatic system is to maintain fluid balance and bring the fluid back to the general circulation. It also is
part of the immune system, helping to protect against disease and infection.

Lymph fluid passes through lymph nodes which can detect pathogens and release white blood cells (lymphocytes).

Lymph flows along the lymphatic vessels due to contraction of the vessels or from external compression via muscular contractions. [1]

Impaired Lymph Clearance Leads to Swelling

Normally, movement of the horse’s legs assists in pushing lymph up out of the lower limbs. However, if the horse is stationary or circulation is impaired due to other causes, the movement of lymph is reduced. [2]

Because the horse’s heart and body mass are higher than the limbs, gravity causes the fluid leaking from the bloodstream and lymphatic vessels to fill spaces in the tissues of the leg, resulting in swelling or edema.

Lower leg swelling can occur with increased lymph production, slower lymph clearance, or both. [1]

Horses have no muscles below their knees to help push lymph back into the body, making them more prone to stocking up. [3]

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Causes of Stocking Up in Horses

Horses in the wild travel vast distances daily, but many domesticated horses have long periods of inactivity. Stocking up is most common in horses that are stalled overnight or after a period of exercise. [1]

While inactivity and gravity naturally contribute to stocking up, there are other factors that make some horses more susceptible to this condition than others.

For example, horses with inflammation of the legs are more likely to stock up. This is because inflammation contributes to fluid leaking from the blood vessels into the leg tissues.

Examples of inflammatory conditions include allergies, local mild dermatitis, and some skin conditions. Excessive exercise or even hoof care changes can also promote inflammation.

Dietary imbalances can cause horses to retain fluid in the legs as well. These could include: [3]

  • Low protein diets
  • Diets with excessive protein
  • Starvation
  • Overfeeding/obesity

Dehydration is another factor that can lead to stocking up. A dehydrated horse may have lower than normal blood pressure, which can reduce the lymphatic system’s ability to push blood back up the leg. [4]

Sodium balance and electrolyte intake also affect how easily fluids move across cells. A horse with low sodium in their diet may be more susceptible to stocking up. [4]

Stocking up may also be a side effect of some medications that cause an increase in blood pressure. It can also be triggered by hot weather in some cases. [1]

Chronic Stocking Up

Chronic stocking up may be a sign of something more serious going on. Chronic stagnation edema may be diagnosed by your veterinarian if your horse persistently experiences limb swelling over a long period of time or if the condition recurs constantly.

Horses can experience chronic stocking up due to the following conditions: [1]

  • Kidney disease
  • Heart failure
  • Chronic lung disease
  • Thyroid disease
  • Liver disease
  • Severe parasite infection
  • Damaged blood vessels
  • Damage or blockage of lymphatic vessels

If your horse experiences chronic stocking up, it’s best to have him evaluated by your veterinarian.

Signs Your Horse is Stocking Up

It’s important to know the signs of stocking up so you can determine whether your horse is experiencing this condition or if it is something more serious.

One thing to note about stocking up is that it is usually not painful. The horse may have mild stiffness and a reluctance to move, but there should be no other signs of illness or injury. The horse should have a normal attitude and appetite. [2]

Stocking up may look similar to other forms of leg swelling, but it is a temporary condition that is easily resolved in most cases.

To determine if your horse is experiencing stocking up, apply pressure with your fingers over the swollen area to see if it leaves an indentation. This should not be painful to the horse, and the pits will slowly refill within 30-60 seconds. [5]

Other inflammatory limb conditions will typically feel harder to the touch and be more painful for the horse.

How To Treat Stocking Up

Stocking up usually resolves after 10-15 minutes of gentle exercise. Movement helps to raise the horse’s heart rate, increasing the return of blood and fluid back to the heart. [3]

With movement, the feet also help force blood and fluid back up the leg and toward the heart. [3]

The horse’s digital cushion – the wedge-shaped structure at the back of the hoof — acts as a pump, which pushes blood and fluid back up the legs. [4] This is why the hooves are sometimes referred to as additional hearts.

If the horse is reluctant to move or if the swelling appears to cause any discomfort at all, you may want to use additional therapies to help resolve the edema.

Cold Water Hosing

Cold water hosing is helpful if the horse appears to be experiencing any pain or if the swelling does not resolve after light exercise.

Applying cold water will reduce any heat in the leg and push fluid back into circulation. [3] Alternating between cold water and heat can be helpful for horses with mild to moderate stocking up.

Ice Compresses or Boots

Another option to reduce swelling in the lower legs is using ice boots, especially if your horse is experiencing any discomfort. [1]

These can be purchased from equine supply catalogues or specialized websites. You can also make your own ice compress us