Intestinal stones can have a huge impact on horse health.
Enteroliths can range in dimension from small pebbles to softball-size stones. Journal photo.
From The American Quarter Horse Journal.
“You’ve got to see this,” the stallion manager said.
He stepped into the mare barn office and came out with what looked like a rock in his hand.
“Wow, a geode,” I said.
“Nope,” he said with a smile. “That’s an ‘enterolith.’”
Enteroliths, which look like rocks, can occur in a horse’s intestine and cause blockage, colic or worse. Dr. Diana Hassel, who spent years researching equine enteroliths at the University of California-Davis shares the symptoms and factors that contribute to enterolith formation. Learn to recognize the signs to improve your horse’s health.
What Is an Enterolith?
The term comes from two greek root words: “enthro,” referring to the intestine, and “lith,” meaning stone; literally, a stone found in the intestine.
They are made up of a variety of minerals and elements, but primarily magnesium ammonium and phosphate. The stones form around a small foreign object such as a piece of wood, metal, plastic or even a small pebble that has found its way into the intestine.
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Diet is the largest contributing factor to their formation. A high mineral content within the large colon and a high, or alkaline, pH can create the ideal conditions. Feeds and hays that create that kind of intestinal environment in a horse link directly to the risk of enterolith growth.
“Alfalfa hay is the biggest risk factor for the disease in the studies we’ve done,” Dr. Hassel says. “It not only provides the mineral content for producing the stone, but also contributes to creating the appropriate pH in the intestine through its buffering capacity.”
However, Dr. Hassel is far from discouraging horse owners from feeding alfalfa to their horses. The richness and mineral content of the hay varies region-to-region, which may make forage testing even more important.
“It all stems originally from the actual soil and water in the area. Those minerals leach into the hay from the soil and water, contributing to the content of the hay. It may be more a function of that, combined with the way horses are managed, than the alfalfa hay itself.” A horse’s water supply may also play a role, as it allows for more impaction.
Certain management conditions – such as limited turnout, stall confinement, infrequent feeding or feeding low-fiber feedstuffs – appear to be the greatest factors. They reduce the movement of bulk feed material through the large intestine, providing a good environment for stones to grow.
“I suspect that there’s a genetic component to the disease, as well,” Dr. Hassel says.
“Not that there’s one horse’s genes that led to this disease,” she clarifies. “I mean differences in those genes that affect the physiology of the intestine.”
How easily enteroliths form in a horse’s intestine might be linked to how a horse’s intestine has been genetically programmed to process particular minerals.
It is unlikely that a horse that may be genetically predisposed will develop stones without the other environmental conditions.
How Do I Know if My Horse Has Enteroliths?
The problem often surfaces as colic, often chronic, of varying degrees of pain that have no apparent explanation.
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The kind of colic usually depends on the size of the stones.
“The softball size, or slightly smaller, are the most dangerous, because they can get into the small colon,” Dr. Hassel says. “They get irreversibly lodged there, cause necrosis and rupture.
Horses with one larger enterolith in the large colon often have a history of chronic colic.
“The larger stones act as a hinge valve,” Dr. Hassel says. “They roll up into place and cause an obstruction, and then roll back away with gravity.”
Unfortunately, the only sure way to tell your horse has enteroliths is to find them, either in manure, via X-ray, or in the intestine after abdominal surgery or necropsy.
Keep in mind that it takes a combination of factors for a horse to form enteroliths: a diet that fosters a high intestinal mineral content and pH, lack of daily pasture turnout, geographic location and sometimes a genetic predisposition to forming them.
Enteroliths have the potential to become very harmful to a horse’s health. If you find one of these out in the pasture or in a manure pile, or if a horse experiences chronic colic that can’t be explained, it may be time to visit the vet.