These are mineral masses also known as intestinal stones that can cause obstruction and lead too colic. When a foreign piece of matter gets in the horse's digestive tract mineral salts are deposited around the object. A foreign object can be such things as gravel, bailing wire, plastic, or twine.
Horses can ingest these objects from eating on the ground, from their hay or grain. I know of horses who consumed alfalfa cubes and developed an enterolith because there was a piece of bailing wire in one of the cubes.
Even if you feed your horse in a feed trough they can still ingest foreign objects. Always check their feed trough and remove any pebbles or other foreign matter.
Possible causes of enteroliths are ingestion of foreign objects, excessive minerals (magnesium, phosphate, or calcium), lack of grazing, diets high in alfalfa (at least 50%) and genetic predisposition can play a part also.
Feeding high amounts of alfalfa tends to raise the pH level in the intestines and with the higher pH it tends to cause the minerals in the alfalfa to accelerate and attach to the foreign objects in the colon and form an enterolith.
If the stones are left untreated they will continue to grow in size because of the minerals they accumulate. Stones can weigh as much as 15 pounds. Horses may have smaller stones, but cause no problems. Some of the stones will be passed in the feces, but the larger stones will cause complete or partial blockage.
Horses who have a higher risk of developing enteroliths are mares, Arabians, Morgans and horses between the age of 5 to 10 years. They are also common in horses located in Texas, California and Louisiana. If your horse doesn't fit into one of these categories it doesn't mean they can't get them as all breeds are potentially susceptible.
Horses with enteroliths may have symptoms that are similar to a colic such as restlessness, lack of manure, sweating, pawing, kicking or biting at the belly, lying down, have no interest in food, manure with mucous, depressed or extremely cranky.
If you have a horse that has chronic colic and with treatment does not get better it could mean they have an enterolith. The only way for an enterolith to be detected is through exploratory surgery or abdominal xrays.
In most cases surgery is the only way to remove them.
Ways to decrease the chances of enteroliths are eliminate bran as it is high in phosphorus, cut back on alfalfa, provide grazing, feed your horse three to four times a day, use straw instead of shavings and frequent exercise.
Always consult your veterinarian if you suspect your horse has enteroliths.