A gastric ulcer is a sore in the stomach lining that occurs when the lining has been damaged by stomach acid and digestive enzymes. Mild stomach ulcers are seen in more than half of foals. In most cases, these ulcers cause no signs and heal without treatment. Ulcers can be found in approximately 30% of adult horses, but the percentage is much higher (up to 90%) in race horses. They are least common among horses turned out onto pasture and most common among Thoroughbred race horses at racetracks. Ulcers are found in 40 to 60% of show horses, event horses, western performance horses, and endurance horses. The prevalence and severity of ulcers increase as the intensity of exertion increases. Stomach ulcers develop in as little as 5 days.

Causes of stomach ulcers vary. Horses' stomachs secrete hydrochloric acid continuously, and the stomach acidity of a horse or foal is very high between periods of eating or nursing, as well as during intensive exercise. The upper part of the equine stomach is lined by tissue that is very similar to the esophagus and is highly sensitive to acid. The lower part of the stomach is more resistant to acid. Continuous grazing leads to low stomach acidity, while intermittent feeding or having food withheld leads to greater acid secretion and ulceration. Exercise may be linked to ulcer formation, possibly due to increased abdominal pressure during exercise pushing acidic stomach contents into the acid-sensitive upper portion of the stomach. The effects of different feeds on stomach acidity and ulcer formation have not been thoroughly studied. Excessive doses of nonsteroidal anti-inflammatory drugs (NSAIDs) are known to induce ulcers, but are not the cause in most cases. Recent research suggests that horses may be infected with a species of Helicobacter, bacteria associated with ulcers in humans. However, a role for this organism in stomach ulcers of horses has not been confirmed.

Most foals with stomach ulcers do not show signs unless the ulcers are widespread or severe. The classic signs for stomach ulcers in foals include diarrhea, grinding of teeth, poor nursing, lying down, and excessive drooling. None of these signs is specific for stomach ulcers, so your veterinarian will also consider other possible causes. When a foal does show signs of ulcers, the ulcers are usually severe and should be diagnosed and treated immediately. Sudden stomach perforation without prior signs sometimes occurs in foals.

Adult horses with ulcers also show nonspecific signs that can include abdominal discomfort (colic), poor appetite, mild weight loss, poor body condition, and attitude changes. In most cases, the signs of ulcers are subtle and may not be associated with the disorder until the horse receives treatment that lowers stomach acidity.

Neither signs nor laboratory tests are specific for stomach ulcers. Endoscopy is the only reliable method of diagnosis for this disorder.

Complications related to stomach ulcers are most frequent and severe in foals and include perforation of the stomach and gastroesophageal reflux (a condition similar to acid reflux in humans). Some ulcers in the region where the stomach joins the intestine can cause constriction; this complication is seen in both foals and adult horses. In rare cases, severe stomach ulceration causes thickening and contracture of the stomach.

Suppressing or reducing the level of acidity in the stomach to protect the stomach wall is the primary treatment objective. This can be accomplished with several types of medication including antacids, histamine type-2 receptor antagonists, and proton pump inhibitors. Proton pump inhibitors are the most effective way to treat and prevent ulcers. One medication, omeprazole, is licensed to treat and prevent ulcers in horses. To treat ulcers in your horse, the veterinarian will consider the animal's overall health and condition, the severity of the ulcer(s), and other factors before recommending a treatment program. Prevention of ulcers is preferable to treatment once they are present. This can be accomplished by a combination of managing the risk factors (feeding schedule, stall confinement, travel, and training) and using medication designed for ulcer prevention.

Last full review/revision July 2011 by Peter D. Constable, BVSc (Hons), MS, PhD, DACVIM; Gordon J. Baker, BVSc, PhD, MRCVS, DACVS; Joseph A. DiPietro, DVM, MS; Walter Ingwersen, DVM, DVSc, DACVIM; John E. Madigan, DVM, MS; James N. Moore, DVM, PhD; Michael J. Murray, DVM, MS; Sofie Muylle, DVM, PhD; Stanley I. Rubin, DVM, MS, DACVIM; Susan D. Semrad, VMD, PhD, DACVIM; Josie L. Traub-Dargatz, DVM, MS, DACVIM