Ulcers occur in horses when the lining of the stomach is eroded due to prolonged exposure to stomach acid. Equine gastric ulcers are a common problem, especially for race and show horses, in part because of the tendency for a disrupted or inconsistent feeding schedule. This lifestyle typically includes stall confinement and periodic feeding, which are known risk factors. Fermented grain, stress, training, hard exercise, medications, and other factors also can contribute.