Stomach ulcers are quite common in horses:

• Up to 93% of racehorses get stomach ulcers, regardless of age.^1,2
• Almost 60% of other performance horses have ulcers.^1,3
• Up to 57% of foals have stomach ulcers, particularly during the first several months of life.^4-6
• 50% of horses with ulcers show no outward signs of gastrointestinal disease.¹

Stomach ulcers in horses are increasingly recognized as a major problem in adult horses as well as foals.⁷ Even when there are no obvious signs of stomach ulcers, they can interfere with performance by affecting training, appetite, and temperament. Ulcers may naturally heal if horses are turned out to pasture for an extended period of time, but they usually don't heal in horses that continue training.

In a recent survey using an endoscope to look inside the stomach, nearly all horses in training had ulcers. (Adapted from: Murray MJ, Schusser GF, Pipers FS, Gross SJ. Equine Vet J . 1996;26:368-374.)¹

Acid is normally produced 24 hours a day in the horse's stomach as a part of the horse's digestive process. When too much acid is present, ulcers result.^8,9

Some factors that increase a horse's risk for stomach ulcers include:

• Feeding. Infrequent grazing or reduced hay intake can lead to stomach ulcers within hours to days.¹⁰
• Training. Intense exercise actually increases acid production in the horse's stomach.¹¹ Performance horses often go without feed several hours of each day during training, permitting acid build-up within the stomach, causing more damage.¹¹ In addition, exercise reduces blood flow to the stomach, but the effect this has on ulcer formation is not known.
• Physical Stress. Foals that are sick, hospitalized, or in pain often get ulcers.^10,12
• Changes in Growing Foals. The stomach of young foals is still developing and is easily injured by acid and enzymes.¹⁰
• Other Factors. Shipping and extended time in stalls expose horses to stresses that may cause ulcers.¹³ Ulcers may also result from certain medications given at high doses.^9,14

If your horse is in training, the chances are high that it has stomach ulcers even if symptoms seem to be absent. Often it's clear only in hindsight, after treatment results in improved attitude, condition, or performance. In fact, by the time obvious symptoms appear, stomach ulcers may be advanced and more difficult to treat. So if in doubt, suspect ulcers until proven otherwise.

• Endoscopy -- examining the inside of the stomach through an endoscope -- can confirm stomach ulcers.¹⁵
• Certain symptoms strongly suggest ulcers. (See table below.)
• Any improvement after treatment with an effective antiulcer medicine suggests that the horse has stomach ulcers, but does not mean that the ulcers have healed. Healing usually requires continued treatment for a period of at least a month -- especially when the horse remains in training.

How should stomach ulcers be managed?

The goals are to:

• Reduce acid.
• Eliminate symptoms.
• Ensure complete stomach healing.
• Prevent ulcer from coming back.

Stomach acid must be controlled at its source to let the stomach lining heal.¹⁰

Changes in management procedures can also be an important part of the treatment program.

Treatment Recommendations

Recommendations for treatment of stomach ulcers include:

• Reduce acidity to allow healing to occur.
• Stop exercising the horse unless using medicine proven effective during training.
• Provide greater access to hay and pasture.
• Reduce obvious sources of stress and treat underlying disease.

Stomach ulcers, even when they do not cause any obvious external signs, can have a big impact on a horse's performance, condition, and health. Improvements in management, treatments, and prevention are leading to better medical and economic outcomes. Check for signs of stomach ulcers in your horses, particularly those in training. Provide earlier treatment using effective medications administered at the correct dosage rate. Change diet and environment to reduce risk factors where possible. Managing stomach ulcers is an important way to help improve your horse's health and maintain a competitive edge. For more information on stomach ulcers and their treatment, ask your veterinarian or go to the gastric ulcer section of The Merck Veterinary Manual to read more about this topic.

1. Murray MJ, Schusser GF, Pipers FS, Gross SJ. Factors associated with gastric lesions in Thoroughbred racehorses. Equine Vet J. 1996;28:368-374.
2. Murray MJ, Grodinsky C, Anderson CW, Radue PF, Schmidt GR. Gastric ulcers in horses: a comparison of endoscopic findings in horses with and without clinical signs. Equine Vet J. 1989;7(suppl):68-72.
3. Hammond CJ, Mason DK, Watkins KL. Gastric ulceration in mature thoroughbred horses. Equine Vet J. 1986;18:284-287.
4. Wilson JH. Gastric and duodenal ulcers in foals: a retrospective study, in Proceedings of the 2nd Equine Colic Research Symposium, 1994, p.126.
5. Murray MJ, et al. Prevalence of gastric lesions in foals without signs of gastric disease: an endoscopic survey. Equine Vet J. 1990;22:6-8.
6. Murray MJ. Endoscopic appearance of gastric lesions in foals: 94 cases (1987-1988). J Am Vet Med Assoc. 1989;195(8):1135-1141.
7. Tremblay R. Gastric disorders and gastric function in newborn foals. Equine Research Centre Newsletter. 1991;5:1-2.
8. Murray MJ. Suppression of gastric acidity in horses. J Am Vet Med Assoc. 1997;211:37-40.
9. Soll AH. Pathogenesis of peptic ulcer and implications for therapy. N Engl J Med. 1990;322:909-916.
10. Murray MJ. Overview of equine gastroduodenal ulceration, in Proceedings of the American Association of Equine Practitioners, 1997, p. 382-387.
11. Pagan JD. Gastric ulcers in horses: a widespread but manageable disease. World Equine Vet Rev. 1997;2:28-31.
12. Furr MO, Murray MJ. The effects of stress on gastric ulceration and serum T3, T4, reverse T3, and cortisol in neonatal foals. Equine Vet J. 1992;24:37-40.
13. Borrow HA. Duodenal perforations and gastric ulcers in foals. Veterinary Record. 1993;132:297-299.
14. Traub JL, Gallina AM, Grant BD, Reed SM, Gavin PR, Paulsen LM. Phenylbutazone toxicosis in the foal. Am J Vet Res. 1983;44:1410-1418.
15. Murray MJ. Disorders of the stomach. In: Smith BP, ed. Large Animal Internal Medicine. St. Louis: LV Mosby, 1990;648-653.