Enteroliths are calcifications or mineral masses that can form in the horse’s intestines, sometimes resulting in impaction colic.

These intestinal stones form when the horse consumes an indigestible object, which is not passed by the digestive system. Mineral deposits then accumulate around the foreign object.

While some enteroliths are naturally passed in the manure with time, others grow larger and can obstruct the transit of feed through the gut.

Enteroliths are most common in horses located in dry, arid regions, but can occur in any horse worldwide. A lack of pasture access and diets containing certain feeds can also increase the risk of enterolith formation.

This article will review the causes of enteroliths, clinical signs, recommended treatment and prognosis for horses affected by intestinal stones. We will also discuss how to prevent the formation of enteroliths in your horse.

Enteroliths in Horses

The term enterolith comes from the Greek terms, “entero”, which means intestinal, and “lith”, which means stone. A horse can have one or more enteroliths that develop over a period of time.

When these stones form in the horse’s gut, the condition is known as enterolithiasis. Interestingly, this condition is rarely found in animals besides horses. [1]

Enterolithiasis is a common cause of colic requiring surgical intervention if the stone results in a partial or complete obstruction of the large or small colon. Horses with enterolithiasis make up a large percentage of surgical colic cases in some areas, such as California. [3][7]

Intestinal obstructions typically occur when stones are transported from the large colon to a smaller-diameter part of the digestive system, such as narrow portions of the small intestines. Alternatively, the enterolith can grow large enough to cause blockage in any location. [4][5]


Enteroliths have been reported as a cause of colic since the 1800s. Historically, horses owned by millers were reported to be more affected than other horses. However, reports of enteroliths decreased in frequency until the 1980s. [6]

Today, California and areas of the southwestern United States have a higher prevalence of enterolithiasis than other areas of North America. [6]

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Causes of Enteroliths in Horses

Researchers have not yet pinpointed the exact cause of enterolith development. However, we do know that stones can form when a foreign body, such as hair, twine, sand, or a small rock, is ingested by the horse and becomes trapped in the gastrointestinal system.

Over time, the object, called a nidus, is coated in layers of minerals called struvite. [8]

Many horses will pass an enterolith with no damage to their gastrointestinal tract. In other cases, the enterolith remains in the intestines, accumulating more layers of struvite and growing quite large. [3]

Horses with a small enterolith may or may not exhibit colic symptoms. Some researchers say that it takes about two years for a stone to become large enough to cause an obstruction.