Photo: UC Davis Center for Equine Health Horse Report

By Jorge Nieto, DVM, PhD, Dipl. ACVS--Reprinted from The Horse Report with permission from the Center for Equine Health, School of Veterinary Medicine, University of California, Davis (UC Davis).


A common case of heartburn can bring intense discomfort, even pain, to a person. Imagine your horse trying to perform with a stomach ulcer. Did you know that the clinical signs of ulcers in horses are subtle and nonspecific and might be reflected in a slight attitude change, a decrease in performance, or a reluctance to train?

Gastric ulcers are common in horses. Their prevalence has been estimated to be from 50% to 90%, depending on populations surveyed and type of athletic activity horses are engaged in.

Gastric ulcers can affect any horse at any age. Foals are particularly susceptible because they secrete gastric acid as early as 2 days of age and the acidity of the gastric fluid is high. Foals that have infrequent or interrupted feeding, or are recumbent for long periods have been found to have lower gastric fluid pH (aqueous solutions with a pH less than 7 are acidic), suggesting that milk has a protective effect against ulcers and that recumbency increases exposure of the stomach to acid.

In adult horses, gastric ulcers occur more frequently in horses that perform athletic activities, with the highest frequency found in Thoroughbred racehorses (80-90%), followed by endurance horses (70%), and show horses (60%). Researchers have found that exercise increases gastric acid production and decreases blood flow to the gastrointestinal (GI) tract.

In addition, when horses exercise, the acidic fluid in the stomach splashes and exposes the upper, more vulnerable portion of the stomach (squamous mucosa) to an acidic pH.

Why are gastric ulcers so common in horses? First, the stomach of the horse is smaller compared with the stomach of other species. Because of this, horses cannot handle large amounts of food; rather, they are built to graze and eat frequent, small portions of feed for extended periods of time.

In a natural grazing situation, the horse requires a steady flow of acid for digestion, so a horse's stomach produces acid 24 hours a day, 7 days a week--up to 9 gallons of acidic fluid per day, even when not eating. In a natural, high-roughage diet, the acid is buffered by both feed and saliva.

Second, understanding the horse's anatomy, it is possible to see how ulcers could be considered a "manmade" disease. When horses are fed two times per day, the stomach is subjected to a prolonged period without feed to neutralize the acid. Furthermore, high-grain diets produce volatile fatty acids that can also contribute to the development of ulcers.

Other risk factors for developing gastric ulcers include physical and environmental stress such as transport stress and stall confinement (intermittent feeding and lack of exposure to other horses). Recent studies have demonstrated that a few hours of transport can induce gastric ulceration in horses that had none prior to departure, as determined by gastroscopy.

Finally, chronic administration of some non-steroidal anti-inflammatory drugs (NSAIDs)--such as phenylbutazone, flunixin meglumine or ketoprofen--can decrease the production of the stomach's protective mucus layer, making it more susceptible to ulcers.

Anatomy of the Horse Stomach

The horse's stomach is divided into two distinct regions: the squamous region at the top (considered a continuation of the esophagus lining) and the glandular mucosa at the bottom (similar to the human stomach). The bottom part is glandular and secretes gastric acid. However, this region also produces mucus and bicarbonate, which protect the mucosa from acid exposure. So even though this region is also exposed to acid for several hours a day, it is not a common place for ulcer formation. When ulcers do form in this region of the stomach, they are usually secondary to chronic NSAID administration.

The top portion of the stomach is designed for mixing of the contents of the stomach and does not have as much protection from the acid. This is the most common place to find gastric ulcers. The lining of this section of the stomach is very thin and does not have many mechanisms for acid protection. Because the horse's stomach produces gastric acid at all times, even when not eating, the squamous mucosa is exposed to acid several hours a day, which can easily erode the lining of this region.

Clinical Signs

The majority of horses with gastric ulcers do not show outward clinical signs. They have more subtle signs, such as:

  • Poor appetite;
  • Dullness;
  • Attitude changes;
  • Decreased performance;
  • Reluctance to train;
  • Poor body condition;
  • Poor hair coat;
  • Weight loss;
  • Excessive time spent lying down;
  • Low-grade colic; and
  • Loose feces.

More serious cases will show abdominal pain (colic) and/or grinding of the teeth. Some horses are found on their backs, commonly seen in foals, since this position seems to provide some relief from severe gastric ulceration. Others will walk away from food for a period of time as if they experience discomfort when the food first hits the stomach.

Clinical signs of ulcers in foals include intermittent colic (after suckling or eating), frequently lying down, intermittent nursing (interrupted nursing due to discomfort), diarrhea, poor appetite, grinding of teeth, and excess salivation. When a foal exhibits clinical signs, the ulcers are likely to be severe and should be diagnosed and treated immediately.

Note that horses that look completely healthy can also have gastric ulcers. Approximately half of the horses presented for colic at UC Davis have gastric ulcers and often it is hard to know whether the colic is the result of the ulcers or the other way around.

Diagnosing Ulcers

The only way to definitively diagnose ulcers is through gastric endoscopy, or gastroscopy, which involves placing an endoscope into the stomach and looking at its surface. This procedure is easy to perform, is minimally invasive, and allows us to evaluate the esophagus, squamous and glandular regions of the stomach, and proximal segment of the small intestine in horses. (See a video of gastroscopy from UC Davis here.)

Since feed material can prevent a complete evaluation of the stomach, horses are fasted for a minimum of 12 hours and water is withheld for four hours before examination.

To minimize stress, we sedate the horse slightly with a short-acting tranquilizer. We then insert the endoscope through the nostril and down the esophagus into the stomach. The light and camera on the end of the endoscope allow the veterinarian to observe the stomach lining. The procedure is very safe, and a complete evaluation takes from 10 to 20 minutes.

Some practitioners will treat a horse for gastric ulcers and look for a change in clinical behavior. This can be helpful but does not answer the question of when to discontinue treatment. Horses that improve with treatment should be scoped prior to discontinuing therapy.

Prevention and Treatment

As always, prevention is preferable to treatment. We have described some common risk factors that can contribute to the formation of gastric ulcers in horses. The following management techniques may assist in preventing ulcers:

  • Feed horses frequently or on a free-choice basis (pasture). This helps to buffer the acid in the stomach and stimulate saliva production, nature's best antacid.
  • Reduce the amount of grain and concentrates and/or add alfalfa hay to the diet. Discuss any feed changes with your veterinarian so that medical conditions can be considered.
  • Avoid or decrease the use of anti-inflammatory drugs. If anti-inflammatory drugs must be given, consider newer ones such as firocoxib, if appropriate.
  • Limit stressful situations such as intense training and frequent transporting.
  • If horses must be stalled, allow them to see and socialize with other horses as well as have access to forage.

A common question asked by horse owners is, "If the prevalence of gastric ulcers is so high, do I need to treat my horse for the rest of its life?" Considering that treatment is expensive and that acid in the stomach is there for a reason, we do not recommend that horses be treated continuously.

Antacids are commonly used in humans to buffer or neutralize gastric acid and protect the mucosa. However, in horses, the dose of antacids required to buffer the pH is high and would need to be used several times a day to be effective. If antacids are used for treating gastric ulcers in horses, they should be used in combination with agents that decrease acid production.

Acid pump inhibitors such as omeprazole and pantoprasole stop gastric acid secretion completely.

Other effective types of drugs for the treatment of ulcers are the histamine type 2 (H-2) receptor blockers such as cimetidine, ranitidine, and famotidine, which partially block acid production.

H-2 receptor blockers work in a similar way to antihistamines used for allergies, except that antihistamines act on type 1 histamine receptors, while the acid blockers act on type 2 histamine receptors. H-2 receptor blockers are less expensive than acid pump inhibitors, but they need to be administered three times a day and only partially block acid production.

Currently, there is only one treatment--omeprazole--approved by the U.S. Food and Drug Administration (FDA) for gastric ulcers in horses. In 2000, the Fédération Equestre Internationale allowed the use of the gastric ulcer medications omeprazole and ranitidine during competition.

Omeprazole is available as a paste formulation and it has been very effective in preventing and treating gastric ulceration in all types of horses. Although the commercial paste is expensive, it is very effective and requires administration once a day. Due to the cost of this product, some compounding pharmacies prepare and sell paste or liquid omeprazole at cheaper prices. However, several studies have shown that the amount of active omeprazole in those products is lower than the label. In addition, the ability of those products to inhibit gastric acid production and their ability to resolve gastric ulcers has been variable.

Horse owners should be wary of claims for products that are not controlled or regulated by the FDA (compounded products) or evaluated in scientific studies. While those products might be less expensive, they could cost you more in the long run.

We recommend treating (1) horses with severe gastric ulceration, (2) horses with clinical signs of gastric ulceration, and (3) horses that are under stressful conditions and at risk of gastric ulceration. Under these circumstances, treatment with a product that is labeled specifically to prevent and/or treat gastric ulcers and approved by the FDA should be used. Treatment should be given for a full month, followed by a recheck endoscopy to confirm complete healing.

A preventative dose of omeprazole is commercially available for use around transport or stressful events. Horses with a history of gastric ulceration may benefit from proactive treatment to decrease the chances of ulcer recurrence. At this dosage, the omeprazole is less costly and could serve as a good investment in your horse's well being.