Visit any show ring, riding arena, or racetrack in North America and the odds are good that many of the equine athletes that you see have equine gastric ulcer syndrome (EGUS). But this condition isn’t limited to performance horses: EGUS also affects young foals and many pleasure horses.

EGUS describes a variety of clinical symptoms including erosions and ulcers in the lower portion of the esophagus, the glandular and nonglandular portions of the stomach, and the proximal duodenum (the beginning of the small intestine).

Gastric ulceration affects a large number of horses of all ages: it’s been shown to be prevalent in 25 to 50% of foals up to two months old, while another study reported that between 80 and 90% of racehorses in training have gastric ulceration