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Many horse owners are familiar with the issue of their horse developing thick legs – called stocked up legs – when confined to the stall for a few days due to illness.
This condition, often referred to as “stocking up” or “stagnation oedema,” is not a novel phenomenon.

But stocked up legs and cellulitis are two different problems

Stocked up legs are easily confused with cellulitis (phlegmon), though they are two very different problems. Cellulitis is a bacterial inflammation in the subcutaneous connective tissue that requires prompt treatment by a competent veterinarian to prevent sepsis, which is the spreading of the infection throughout the body.
Cellulitis typically affects a single leg, while stocking up occurs when multiple legs are involved, and the swelling subsides after approximately 10-15 minutes of gentle exercise.

In most horses, the hind legs are the first to be affected, although in some cases, the front legs may also swell as the condition progresses. The swelling usually initiates in the distal area, just above the hoof. It becomes noticeable when the fetlock joint is no longer clearly defined, or the swelling extends further up the cannon bone, making the tendons less discernible.
While many horses experience stocking up after prolonged periods of standing, there are also individuals who exhibit “spongy” legs despite being housed in open yard with ample exercise opportunities.

However, the question remains: why do some horses develop thick, stocked up legs while the horse in the neighboring stable maintains normal legs, even with less movement?

Surprisingly, scientific literature on this topic is scarce, despite the widespread nature of the phenomenon known to almost every horse owner (though hopefully their own horse remains unaffected). What is currently known includes the following:

  • Movement plays a crucial role, as extended periods of standing promote stocking up and swelling of the legs
  • Horses kept in closed stables are more susceptible to this condition compared to those housed in open yards.
  • Shoeing may also be a contributing factor.
  • Affected horses often exhibit early indicators of kidney issues.
Boxenhaltung
© Adobe Stock/Ralf Geithe

Standing adversely affects horses’ legs

We all know that movement plays an important role. This is evident from the rapid reduction in swelling when a horse is allowed to walk for a little while. The vascular structure of horses accounts for this phenomenon. The heart functions as a pump, pumping blood to the extremities to supply the tissue there with oxygen and nutrients. But as it is not a suction device, the venous blood can not be drawn back towards the body.

The hoof pump: the counterpart to the heart

This crucial task falls upon the hoof pump: with every step, the hoof expands and contracts. This causes the blood to effectively be propelled back towards the heart through the venous system.
A frequently walking horse can pump blood out of the hooves very effectively, enabling the inflow of fresh oxygenated blood to nourish the tissues. Conversely, prolonged periods of standing result in increased pressure within the capillaries due to the pumping action of the heart from above, coupled with inadequate drainage since the hoof pump is not in operation. Consequently, fluid is forced out of the blood vessels into the surrounding connective tissue, leading to visible swelling.

Upon resuming movement, the hoof pump not only facilitates the removal of venous blood from the leg, which reduces capillary pressure. It also activates the lymphatic system, pumping any accumulated lymph fluid towards the body.

Any disruption to the function of the hoof pump, whether caused by extended periods of standing or constrictive shoeing, can contribute to the development of stocking up.

This explains why horses kept in single stables are more prone to this condition, as they spend less time in motion and more time standing throughout the day compared to horses in open yards or track systems. However, not every shod horse confined to a stable at night stocks up, indicating the involvement of additional factors.

According to Chinese Medicine, the spleen is responsible for keeping things in their rightful places

According to the principles of Chinese medicine, the spleen plays a crucial role in maintaining the proper distribution of body fluids, ensuring they remain where they are supposed to be: within blood or lymph vessels. Consequently, lymph seepage into the connective tissue is associated with weakened spleen energy.

While the spleen remains a relatively unfamiliar organ to many, it plays an indispensable role in a well-functioning immune system and blood purification. Recent studies have also revealed its contribution as a “secondary pancreas” in regulating blood sugar levels. The long-held belief in Chinese medicine that the spleen weakens due to excessive sugar consumption aligns with these findings.

Sugar contributes to stocking up

This is why high sugar diets often lead to the development of lymphatic swellings, such as in the flanks, along the neck crest, in the sheath pocket or in front of the udder, or in stocked up legs.
High sugar contents also impose strain on the kidney function, as extensively documented in diabetes research spanning decades. The kidneys play a crucial role in maintaining the body’s water balance. If their functioning is compromised, excess water is retained. To prevent a dangerous rise in blood pressure within the vessels, this surplus fluid is “temporarily stored” in the connective tissue.

Therefore, stocked up legs are always the result of a combination of an impaired hoof pump (due to lack of exercise or restrictive shoeing) and a metabolic issue.
Often, hidden sources of sugar and starch in the feed are implicated.
This can range from high-sugar hay to concealed sugars in apple pulp or carrots, and even hidden starch in mashes or treats. It is worthwhile to carefully examine and significantly reduce the sugar/starch content in the feed.

By also supporting kidney function, such as with appropriate herbal supplementation, and ensuring the proper functioning of the hoof pump, most horses can maintain slender and shapely legs even after a day of standing.

Team Sanoanimal
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