What To Do About Equine Enteroliths

Enteroliths are mineral accumulations of magnesium-ammonium-phosphate (struvite) around a foreign object (a piece of metal, pebble, baling twine, hair, rubber) that form round, triangular, or flat stones inside the bowel, usually over the course of multiple years. They form in the large colon of horses, where they can remain for some time until they move and cause an obstruction in the large or small colon, resulting in colic.

Enteroliths form as a result of certain diets (for example, feeding diets high in magnesium and protein, such as alfalfa-rich diets), breed predisposition, and/or management practices. The rate of enterolith formation is variable and thought to be affected by gut pH, the availability of certain minerals, and gut motility. Enteroliths can vary in size, and horses may carry one or two large ones, or 100 or more small ones, in their guts. Why some horses develop enteroliths and others do not, as well as why some horses develop many stones whereas others develop only one or two, is not well understood. Small enteroliths may harmlessly pass out of the body with manure, whereas large stones can create obstructions and result in colic. Many horses can carry large enteroliths for years with no issues.

Enterolithiasis is reported worldwide, but is more common in certain geographic regions, particularly California and Florida.  It also occurs in all breeds, but some, including Arabians and Arabian crosses, Morgans, and American Saddlebreds, seem to be overrepresented. There does not appear to be any sex predilection and enteroliths are very rare in horses under two years of age.

What are the clinical signs of enteroliths?

Clinical signs vary depending on the size and number of enteroliths and the part of the bowel where they are located. Horses with a single large enterolith in the large colon may have a history of chronic, intermittent colic. Horses with smaller-size stones that can move and lodge within the small colon will have signs of colic that are more acute. Some horses have a history of passing stones in the feces without showing signs of colic. Nonspecific signs, such as changes in attitude, anorexia, lethargy, weight loss, loose manure, girthiness, and reluctance to exercise may appear prior to any signs of colic. Signs indicating mild to moderate abdominal discomfort include pawing, repeatedly lying down and getting up, rolling, looking at the flank, kicking at the abdomen, and sweating.

How are enteroliths diagnosed?

Diagnosing enteroliths can be challenging, as many of the initial outward signs are not