Enterolithiasis is the obstruction of the flow of ingesta or gas associated with the presence of enteroliths (solid, rock-like masses also known as intestinal stones) which form in the ampulla coli of the right dorsal colon of horses. Enteroliths are typically composed predominantly of struvite, a composite of magnesium ammonium phosphate.
Enteroliths are found most often in horses on a high-protein diet with elevated levels of magnesium; such as that found in horses consuming large amounts of alfalfa hay or wheat bran. The Arabian breed, female horses, horses which are not on a consistent feed routine, and horses routinely kept indoors with minimal turnout, have an increased risk of developing enteroliths.
Clinical signs seen in horses with enteroliths vary based on their shape and location within the colon. Sometimes the presence of enteroliths will have little effect, be passed normally through feces, or cause mild, recurrent episodes of colic. Other times, they can cause a complete obstruction which produces severe colic symptoms.