Enteroliths are stones that form in the large bowel of horses, usually in the right ventral colon. Phytobezoars are concretions of vegtable matter that form in the stomach or small bowel. These stones, over months or years, can grow quite large. If they become to large to pass they may result in temporary recurring obstruction and a recurring colic that is difficult to diagnose. The obstruction may become permanant and fatal. This article discusses causes, clinical signs, diagnosis, treatment, and prevention.

Stones and phytobezoars usually start around a small object called a nidus which seems to act as a "seed" for the stone to begin growing. The most common nidus for enterolith formation is hair, small metal objects, or silica stone. Around this nidus a concretion of minerals and organic matter form and harden. Phytobezoars are often associated with the ingestion of persimmons with the seeds acting as a nidus for ingested vegetable matter.

Mean pH of colonic contents from horses with enterolithiasis was significantly higher than for control horses. Also horses with enterolithiasis had significantly lower percent dry matter in colonic fecal samples and higher mean mineral concentrations than controls. Recently it has been noticed that Arabs seem a little more predisposed to enteroliths. Alfalfa hay feeding is strongly correlated to enterolith incidence. California grown alfalfa hay is particularly high in mineral content.