Gastric ulcers may be an important source of gastrointestional problems in foals and adult horses under stress. The prevalence and severity of ulcers in an adult horse will increase as stress increases. A horses with a nervous disposition is more likely to have ulcers than a quiet or easygoing animal. Horses under intense training, such as race horses, tend to have moderate to severe gastric changes and up to 90% of racing horses may be affected. A 1999 endoscopy study published in the AVMA journal stated that the researchers detected ulcers in 58% of horses in active training and horses being shown in three day events. The horses in this study were transported to at least one event in the thirty days prior to the endoscopy.

Horses are programmed to eat constantly. The equine stomach will secrete hydrochloric acid continuously, whether a horse is eating or not. Hydrochloric acid is thought to accumulate at very high levels during periods when a horse is not eating or nursing. Unless there is something in the stomach, such as saliva or alkaline feed, the stomach will not be buffered from the acid. The effect of diet on ulcer development has not been fully studied. It has, however, been shown that good quality hay may reduce the severity and occurrence of ulcerations. The use of NSAID or nonsteroidal anti-inflammatory drugs can cause an increase in the presence of ulcers. The role of Helicobacter spp., a bacteria found to cause human gastrointestional ulcers, is presently unknown in the horse.

Horses typically exhibit clinical symptoms related to abdominal discomfort or colic. The appetite in these animals is decreased and they may exhibit weight loss and poor body condition. In chronic cases horses may have a rough haircoat and, in general, appear unthrifty. Foals and animals with severe cases of ulcers may have diarrhea, possibly with digested blood that would be exhibited by a dark tar-like feces and anemia. Ulceration occurs primarily in the duodenum in foals. Gastric perforation and blockage can occur in severe cases. If perforation occurs peritonitis will result and an elevated white blood cell count will become apparent. Sometimes back soreness and hind end stiffness will be seen as clinical signs relating back to the abdominal pain caused by ulcers. Gastric ulcers can only be detected through an endoscopic exam.

Omeprazole is the only medication currently approved for use in the treatment of ulcers in horses. The product is manufactured by Merial and comes as a 2.28 gram oral paste in a prepackaged syringe. The trade name of this product is GastroGuard®. Omeprazole is administrated orally once a day at 0.45 mg/lb for 28 days. In a 600 to 1200 pound horse, ¼ of a syringe would be given orally daily. Horses greater than 1200 pounds would receive ½ of the oral paste syringe daily. Omeprazole is a proton pump inhibitor which blocks the production of stomach acid. Horses that are known to have ulcer problems should be given GastroGard® before, during, and after stressful events. Animals on medication known to induce ulcers should also be given GastroGard® as a preventative to ulcers which can develop as a result of treatment. The comparable drug for human use is Prilosec.

To prevent ulcers it is recommended to feed horses small meals throughout the day. Good quality hay should be available at all times for munching. If a horse is overweight, do not feed it as much grain, but allow it access to hay at least six times daily. Preferably, have hay available at all times to simulate the natural environment of the horse.