by Karen Briggs
Enteroliths aren’t an everyday occurrence. They’re rare and fascinating oddities, something to be observed in a jar at the vet hospital… but if your horse is harboring them in his gut, they can be a death sentence.
Think of them as the equine equivalent of a pearl. Enteroliths form when a foreign object of some kind ends up in the gastrointestinal tract. It can be as insignificant as a sliver of wood, or perhaps a piece of binder twine that didn’t get sorted out from the hay.
If the body fails to expel the indigestible particle, it tries to protect the gut from it instead, by forming layers of mineral deposits around it, generally composed of magnesium, phosphates, and ammonium. (Calcium, iron, aluminum, nickel, and other minerals are also found in some cases.)
The result is a stony concretion that may be smooth and spherical, irregular and bumpy, or even polyhedral, depending on the original shape it’s trying to cover up and the crystalline structure of the minerals involved.
Enteroliths can range from pea-sized to ones larger than your fist. Small ones are generally passed out in the manure (eventually), but larger ones can be responsible for mysterious, recurrent colic, and need to be surgically removed before they cause a fatal intestinal rupture.
Enteroliths can occur anywhere, and can strike any breed. In one study, there was some indication that older horses (median age 11.5 years) were more likely to have enteroliths than younger ones, but that could be because the stones can take years to develop.
Diagnosing enteroliths is usually done by a combination of radiographs and surgical exploration. The chances of detecting an enterolith by x-ray depend on its location, its size, and the size of the horse (the smaller the stone, and the larger the horse, the more likely it is that it will elude the radiographs).
Fortunately, the success rate for removing the stones is upwards of 90% – but of course, this type of abdominal surgery is always risky.
Prevention, of course, is the best policy. A few tips to help reduce the chances that your horse will develop an enterolith:
• Eliminate, as much as possible, the chance that your horse will ingest a foreign object by removing binder twine from hay every time you open a bale, and checking his surroundings and paddocks for debris and garbage.
Rather than feeding directly on the ground, try a ground-level feed tub or hay feeder.
• Feed grass hay. About 98% of horses with enteroliths have a diet of at least 50% alfalfa hay, which has much higher levels of calcium, magnesium, and protein than grass hay.
Excess protein is converted to urea and ammonia before it is excreted, and the ammonia may contribute to the build-up of stones.
• Reduce or eliminate wheat bran from the horse’s diet. Bran provides high levels of phosphorus, which may contribute to enterolith formation as well as mineral imbalances in the bones.
• High pH levels in the large intestine seem to increase the risk of enteroliths. Decrease the pH levels in the gut by adding a cup of apple cider vinegar a day to the diet. (Vinegar is a mild acid.)
• When the gut isn’t actively moving feed material along its length, it may be providing a favourable environment for enteroliths to incubate and grow.
To keep the digestive system occupied, provide free-choice hay, and increase the number of feedings each horse gets to three to four small ones per day, rather than one or two large meals. Don’t worry if the hay is a little coarse and stemmy – the indigestible fibre actually contributes to GI tract health.
• Provide daily exercise and avoid prolonged stall confinement. Inactivity also contributes to reduced intestinal movement of feed.
• Bed on straw instead of shavings. Though normally we discourage horses from eating their bedding, in this case munching on straw may be a plus – it provides high fibre, bulky feed material throughout the day, and it’s low in magnesium, phosphorous, and protein.
