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Key takeaways

Enteroliths are rock-like masses that form in the large intestine when a foreign body becomes coated in mineral deposits.

  • Enteroliths range in size and number in affected horses
  • The risk of enteroliths ranges from mild cases causes only minor colic to life-threatening causing gastrointestinal blockage
  • The cause of enteroliths is not known, but relates to the level of acidity within the intestine
  • Diagnostic tools include physical examination, rectal palpation, imaging, and exploratory surgery
  • Treatment, if needed, is surgical
  • Prognosis is good if detected early
  • If rupture occurs, the prognosis is grave
  • Prevention aims to keep the appropriate intestinal pH balance
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A closer look: Enteroliths in Horses

Enteroliths are common in horses. Enteroliths that move through the digestive tract without getting stuck or damaging surrounding structures often pass with manure unnoticed. Large enteroliths that remain in the intestines without blocking the passage of food or water also are not cause for concern.

The movement of enteroliths within the intestinal tract can cause discomfort, leading to mild, moderate, or intermittent abdominal pain which benefits from immediate attention from a veterinarian. Mid-sized or large enteroliths that obstruct the passage of food cause severe abdominal pain and require emergency veterinary attention.

Risk factors

The severity of enteroliths in horses depends on how large they are, how many there are, and whether they get stuck in one of the structures of the gastrointestinal tract. Enteroliths causing an intestinal obstruction can lead to swelling of the intestine, and in severe cases, intestinal rupture.

In severe cases, a large enterolith becomes big enough to block the passage of food or a mid-sized enterolith passes from the the large intestine to the much smaller rectum, where it gets stuck. These cases result in severe abdominal pain, which requires emergency veterinary attention.

Enteroliths can occur in any horse, but middle-aged and older horses are more susceptible, especially mares. Horses in certain geographical areas where alfalfa hay is a large part of the diet, such as the south west of the United States, Indiana, California, and Florida also have higher incidence.

Genetics also play a role in enterolith risk. Breeds that have a higher than usual incidence include:

  • Arabians
  • Morgans
  • Miniatures
  • Appaloosas
  • Saddlebreds
  • Donkeys

Possible causes

The precise cause of enterolith development is not known. In some horses, when a foreign body is ingested, such as hair, twine, sand, or rocks, the gastrointestinal tract coats the object in layers of minerals called struvite. Usually, the horse passes the enterolith, often with no damage to the gastrointestinal tract. In other cases, the enterolith remains in the GI tract, accumulating further layers of struvite.

Development of enteroliths is associated with:

  • Low acid level of the intestines caused by hereditary factors
  • A diet rich in alfalfa, which promotes crystallization of minerals
  • Higher concentrations of minerals, especially magnesium, in the diet, hard water, or other environmental elements
  • Lower gut motility due to genetic predisposition or environmental factors such as a lack of turnout and exercise

Main symptoms

Colic ranges from mild to severe. The severity of colic signs depend on the size of the enteroliths, and whether the passage of food is blocked.

In cases where enteroliths are present, but pass through the gastrointestinal tract only causing occasional blockages, signs of colic are intermittent.

Testing and diagnosis

Diagnostic tools to identify enteroliths include:

  • Physical examination
  • Rectal palpation
  • Diagnostic imaging, such as ultrasound and X-rays
  • Surgical exploration

Steps to Recovery

Treatment is surgical removal of the enterolith. In cases where the intestine is damaged, removal of the damaged tissue is also required. Horses often require supportive care to alleviate symptoms while they are being prepared for surgery. Supportive care may include:

  • Pain medications
  • Passing a nasogastric tube to reduce stomach fluid accumulation
  • IV fluids

Note: intubation should only be performed by a veterinarian. There is no safe way to intubate a horse at home.

The prognosis for enteroliths is excellent, if they pass or remain in place without damaging the surrounding structures. In cases where they cause obstruction and surgery is required, the prognosis is good, as long as the intestinal tract has not been damaged significantly. In cases where enterolith obstruction results in the rupture of the intestine, the prognosis is grave.

Horses that have passed enteroliths are likely to have more in their bodies, or develop them again.


Preventative measures aim to optimize gastrointestinal health, control the acidity level in the intestines, and lower mineral intake. Strategies for avoiding enteroliths include:

  • Reducing alfalfa in the diet
  • Providing daily turnout and exercise
  • Providing many small meals throughout the day
  • Using feeders to keep hay off the ground to avoid sand, gravel, and other foreign objects
  • Supplementing with psyllium to control sand colic
  • Softening hard water
  • Avoiding mineral-rich feeds such as wheat bran
  • Adding apple cider vinegar to the feed to help dissolve ingested minerals

Are Enteroliths in Horses common?

Enteroliths are common in horses. Enterolith obstruction is less common.

Typical Treatment

  • Surgical intervention
  • Supportive care


James N. Moore , DVM, PhD, DACVS - Writing for Merck Veterinary Manual
- Writing for EQUUS Magazine

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