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Why Do Horses Get Ulcers, & What Can I Do About It?

Riding a horse at sunset

Are you and your horse training hard for the next competition? Are you treating your horse for a minor lameness? Then your horse could be a prime candidate for gastric ulcers development.

The horse has been designed to allow maximum digestion of coarse fibrous plant materials that complement their natural grazing lifestyle. Horses that are allowed to graze, nibble on food continuously throughout the day. This pattern of behavior is known as a “trickle feeder.” A trickle feeder is consistently eating, chewing, salivating and swallowing repeatedly over a 24-hour period.

The horse’s digestive tract is evolutionarily adapted to making use of bacteria and other microorganisms to convert structural carbohydrates and digestively inaccessible proteins, vitamins and minerals found in plants, who then process them into absorbable nutrients capable of meeting their nutritional needs.

Since horses are programmed to eat constantly their stomach will secrete hydrochloric acid continuously, whether the 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. Saliva acts as a natural antacid for the horse. Horses that are not allowed to graze or have free access to hay will eat whatever they can to produce saliva, including manure and the wood from stalls, resulting in behavioral problems in addition to gastric ulcers.

Intensely managed horsed are often fed high levels of starches and other nonstructural carbohydrates, oils, fats and proteins. Volatile fatty acids are produced as byproducts of bacterial fermentation of carbohydrates. The volatile fatty acids cause damage to the stomach lining which may result in the formation of gastric ulcers in as little as two hours. The level of volatile fatty acids necessary to produce ulcers can be achieved when grain is fed at a level of one pound per 200 pounds of body weight in just one feeding. These easily digestible feeds do not require additional breakdown in the hind gut. This is probably why so many intestinal problems exist in artificially fed horses.

Stress is also an important source of gastric ulceration. A horse with a nervous disposition is more likely to have ulcers than a quiet or easy going 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 detected gastric ulcers in 58% of horses in active training and those being shown in three day events within the last 30 days.

The use of non-steroidal anti-inflammatory drugs (NSAIDS) may also increase the incidence of ulcers. The role of Helicobacter spp., a bacteria found to cause human gastrointestinal ulcers, is presently unknown in the horse.

Horses typically show clinical signs related to abdominal discomfort or colic when suffering from gastric ulcerations. 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 hair coat 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 tarry feces and anemia. Ulceration occurs primarily in the duodenum in foals. Gastric perforation and blockage may occur in severe cases. When 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 confirmed through anendoscopic 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 GastroGard® in the prescription formula or UlcerGard® in the over-the-counter product. 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 such as nonsteroidal anti-inflammatory drugs should also be given GastroGard® as a preventative to ulcers which may develop as a result of treatment. The comparable drug for human use is Prilosec.

Gastrointestinal ulcers are largely a result of modern management practices and domestication. To prevent ulcers, it is recommended that the horse be feed small meals throughout the day. Good quality hay should be available at all times for constant munching. If a horse is overweight, decrease the amount of grain that is fed, but allow access to hay at least six times daily.


  • Kahn, Cynthia Editor: The Merck Veterinary Manual. 9th Edition.
  • King, Marcia. “Ulcer Studies Solidify Causes, Treatments.” Veterinary Practice News. November 2007. Pp. 30.
  • Knottenbelt, Derek. “Does Hind Gut Pathology Exist or Matter? Veterinary practice News. June 2016. P. 42.
  • “New Test Detects Occult Blood.” Veterinary Practice News. November 2007. Pp. 34.
  • Tremayne, Jessica. “The Obesity Problem.” Veterinary Practice News. March 2011. Pp. 46-47.
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