Enteroliths in Horses: Signs, Causes, Treatment and Prevention in California

Veterinary surgeons at the University of California, Davis see enteroliths in horses more often than almost any other kind of surgical colic. An enterolith horse can look perfectly healthy while a stone grows for years inside the large intestine. Then one day it stops eating and starts to roll.

What enteroliths in horses are, and how they form

Enteroliths in horses are mineral stones that build up in rings around a small nucleus in the colon, often a swallowed fragment of wire, a pebble or a piece of hay twine. It is usually round or shaped like a tetrahedron, and most are struvite, a compound of magnesium, ammonium and phosphate. They can reach the size of a softball or larger.

Why do they form? The best-supported explanation is a gut chemistry that is too alkaline and too rich in magnesium and protein. A horse eating mostly alfalfa, which is high in all three, gives the process what it needs. Slow gut movement helps the stones grow, because mineral has more time to settle on the surface.

The main causes and risk factors

The causes of enteroliths in horses are still being worked out, but diet is the headline. A study of California horses found that those with enteroliths ate a significantly higher share of alfalfa and were less likely to have daily access to pasture. Stall confinement shows up in nearly every study, which suggests that grazing, with its steady trickle of fiber, gives some protection.

Geography matters too. Cases cluster in California, Texas, Florida and Arizona. One explanation points to alfalfa grown on serpentine soils, which pull extra magnesium into the plant. That is a suggestion rather than a proven chain, but it fits the pattern that California vets describe.

Breed adds a second layer. Arabians and Morgans appear most often in the research, and miniature horses and some others are also overrepresented, though any breed can be affected when the diet is right for it. Enteroliths are rare in horses under two. Most affected horses are middle-aged or older, which makes sense for something that takes years to build.

Early signs and horse enterolith symptoms: what the barn sees first

Horse enterolith symptoms are vague at first, and that is the trouble. A horse may have a bout of mild colic that clears up by itself, then another a few weeks later. Appetite dips. Manure gets smaller or less frequent. Those are early signs, and any one of them alone proves nothing. Some animals lose weight or turn dull under saddle, and owners put it down to age or mood.

When a stone moves into a narrow part of the colon and wedges there, the picture changes in hours. The horse paws, looks at its flank, lies down and gets up repeatedly, may sweat and stops passing manure. That is an emergency. Call the vet at once, and do not give medication unless the vet tells you to.

The horse enterolith symptoms that matter most are the repeated mild episodes, and those are the part most owners miss. A horse with a history of recurring low-grade colic, especially in a California barn that feeds a lot of alfalfa, is a candidate for investigation. Vets use rectal exams, ultrasound and radiographs, and radiographs of the abdomen can sometimes show the stones directly, which is why a diagnosis often comes before the treatment plan rather than during an emergency.

When to call the vet

Colic is an emergency whatever the cause, and the sorting happens on the phone. Call at once for a horse that is pawing, rolling or trying repeatedly to lie down, looking at its flank, sweating without work, or standing stretched out and refusing feed. Call the same day for a smaller pile than usual, a skipped meal or a horse that is quieter than normal.

While waiting, take the feed away, note the pulse, the gum color and the time of the last manure, and keep the horse where it cannot hurt itself. Painkillers wait for the vet, because they can hide the signs the vet needs to read.

Treatment: surgery, recovery and follow-up

An enterolith that blocks the intestine must be removed surgically if the horse is to live. The surgeon opens the abdomen under general anesthesia, locates the stone and takes it out through an incision in the bowel. An enterolith horse that reaches the table before the intestine is badly damaged has a good outlook, and many return to their former work. Treatment decisions turn on how long the blockage has lasted.

After surgery most horses are rested for about three months and brought back gradually. Vets typically tell owners to stop feeding alfalfa altogether, since the diet that grew the first stone will grow another. Recurrence is a real risk, and some horses need a second operation.

Cost and risk are the practical facts of treatment. Colic surgery is expensive, and many owners keep an insurance policy or a savings fund for it. Whether to operate on a given horse is a decision the vet and the owner make together, after an examination.

Other causes of colic worth ruling out

Colic is a symptom, not a diagnosis, and stones are one cause among many. The first aid kit page lists the signs to watch and what to do while waiting for the vet. Gas, impaction, a shifted loop of bowel, sand in the gut and sudden diet changes all produce the same pawing and rolling, and most episodes are mild and settle with veterinary treatment at the farm. That is exactly why enteroliths are missed: each small episode looks like ordinary colic and gets treated as such. A history of repeated episodes, a taste for alfalfa and a stall-kept routine are what move a stone higher on the vet’s list, and they are worth writing down with dates.

Prevention: feed, pasture and water

Prevention is mostly feed, and the main causes of stone formation are the ones an owner can change. Many vets recommend that alfalfa make up no more than about half of the ration for horses at risk, and some advise far less, with grass hay filling the rest. Feeding from the ground in natural position helps gut movement. The hay calculator shows how many pounds a day a ration of a given weight adds up to.

Daily pasture, when it is available, gives horses the slow grazing that stall-fed animals miss. Exercise supports normal gut motility, which is one more reason horses in regular work, like the trail and distance horses on the riding hub, tend to do better than idle stall-kept ones. Water must always be available, clean and cool in summer.

Owners can also lean on a few habits from the horse care guide: learn a horse’s normal manure output, notice the first small change, and keep a vet’s number on the barn wall. A horse that changes its manure pattern is giving an early warning, as covered on the manure management page.

Questions to bring to the vet

A routine visit is the cheapest time to talk about stones, and a short list keeps the conversation useful.

Start with the ration. What share of the hay is alfalfa, and would a hay analysis help? Labs report protein, calcium and magnesium for a sample, which gives the vet numbers in place of guesses. Ask whether this horse sits in a higher-risk group because of breed, age or a day spent mostly in a stall.

Then agree on the warning signs. A smaller pile, a skipped meal or a horse that stands stretched out can each mean something or nothing, so the useful question is which changes should trigger a call for this particular animal, and which are an emergency at any hour. Know in advance which clinic handles colic surgery after hours and how long the trailer ride is.

Finally, ask what a horse with repeated mild colic should have done: rectal examination, ultrasound or abdominal radiographs. Ask what transport and surgery would cost, and whether insurance or a savings fund is in place. Write the answers beside the barn phone, next to the vet’s number.

The UC Davis Center for Equine Health publishes a clinical summary of enterolithiasis.

The California alfalfa finding comes from a 2004 case-control study of dietary risk factors.