Enteroliths in Horses: Intestinal Stones and Recurrent Colic

Enteroliths are stone-like mineral masses that form inside a horse's intestinal tract, most often in the large colon. They are usually made of magnesium ammonium phosphate and often build up around a small central object, such as a pebble, bit of metal, or other material that acts like a starting point for the stone.

These stones may sit quietly for a while, then start causing recurrent mild colic as they partially block the intestine. In other horses, the first obvious problem is a more serious obstruction with stronger pain, rising heart rate, and worsening abdominal distension. Because the signs can come and go, some pet parents are told their horse has had "mystery colic" more than once before the real cause is found.

Enteroliths are reported more often in certain parts of the United States, including California, the Southwest, Indiana, and Florida, and they are seen commonly in Arabian horses. Most affected horses are around middle age, and horses younger than 4 years are affected less often. The good news is that when the problem is recognized and treated promptly, outcomes after surgery are often favorable.

Enteroliths form when minerals in the intestinal contents gradually deposit in layers around a small core. Researchers do not think there is one single cause. Instead, enterolith formation seems to involve a mix of diet, intestinal chemistry, geography, breed predisposition, and management factors.

A diet high in alfalfa hay is one of the best-known risk factors. Alfalfa can raise intestinal pH and contributes minerals that may support stone formation. UC Davis advises limiting alfalfa to less than 50% of the diet for horses at risk, and horses that have already had enterolith surgery are generally advised to avoid alfalfa entirely.

Breed also matters. Arabians and Arabian crosses are consistently overrepresented, though enteroliths can occur in many breeds, including Morgans and American Saddlebreds. Regional patterns suggest that local water and feed mineral content may also play a role. Limited grazing time, less consistent exercise, bran-heavy feeding, and mineral-rich rations are often discussed as contributing factors.

It is important to remember that risk factors do not guarantee disease. Some horses on similar diets never develop stones, while others do. That is why your vet will look at the whole picture, including your horse's diet, location, breed, age, and history of recurrent colic.

Diagnosis starts with an urgent colic exam. Your vet will assess pain level, heart rate, hydration, gum color, gut sounds, and manure output. A rectal exam may show intestinal distension, but the stone itself often cannot be felt. Bloodwork and sometimes abdominal fluid testing may help your vet judge how sick your horse is and whether referral is needed.

Abdominal radiographs (x-rays) are the best screening test for enteroliths, especially in regions where they are common. Still, x-rays do not catch every case. Detection depends on the horse's size, how much feed is in the bowel, where the stone is located, and the imaging equipment available. Ultrasound can help evaluate colic, but it is usually less definitive than radiography for confirming an enterolith.

If your horse has recurrent colic and the diagnosis remains uncertain, referral to an equine hospital is often the safest next step. In some horses, the diagnosis is strongly suspected before surgery but only confirmed during exploratory celiotomy. Because enteroliths can progress from intermittent obstruction to a complete blockage or even rupture, timely decision-making matters.

Prevention focuses on lowering risk, not guaranteeing that stones will never form. If your horse has had recurrent colic, is an Arabian or Arabian cross, or lives in a region where enteroliths are common, ask your vet to review the full feeding and management plan.

The most practical step is usually diet adjustment. Horses at risk are often managed with less alfalfa, and UC Davis recommends limiting alfalfa to under 50% of the diet. Horses that have already had enterolith surgery are generally advised to avoid alfalfa. Your vet may also suggest reducing bran-heavy feeds, avoiding mineral-rich rations when possible, and reviewing water sources if hard water is a concern.

Management matters too. More consistent turnout, grazing time, regular exercise, and frequent feedings may help keep intestinal contents moving more normally. Some horses may benefit from psyllium or other diet changes, but those decisions should be individualized with your vet because prevention plans depend on the horse's whole ration and medical history.

If your horse has had even one unexplained colic episode that keeps coming back, prevention also means not waiting too long to investigate. Recurrent mild colic is often the clue that leads to diagnosis before a complete obstruction develops.