Gastric ulcers are lesions in the horse’s stomach that can cause pain, recurrent colic, poor exercise tolerance, weight loss and behavioural changes in your horse.

Ulcers in the squamous (upper) region of the stomach form when gastric acids come into direct contact with the stomach lining, resulting in erosion of the mucosal barrier. Intermittent feeding, large concentrate meals, high-intensity exercise, and stress can contribute to the development of gastric ulcers.

The glandular (lower) region of the stomach has evolved mechanisms to deal with constant contact with gastric acids. When these protective mechanisms are weakened, ulcers can develop. Stress, illness, and nonsteroidal anti-inflammatories (NSAIDs) can all compromise the protective barrier of the glandular region.

Less than 10% of ulcers resolve on their own without treatment. And unless the underlying cause(s) of the ulceration are addressed, gastric ulcers are likely to recur – particularly in performance horses.

Fortunately, there are a number of effective treatments for equine ulcers that involve both feeding and management changes as well as medications, such as omeprazole. Most ulcers heal within 1-2 months given the right recovery plan.

In this article, we will discuss what ulcers are, why they occur and the best treatment options available for your horse.

What are Gastric Ulcers?

Equine Gastric Ulcer Syndrome (EGUS) is found in adult horses and foals alike and is classified as a performance-limiting disorder.

Ulcers are detrimental to the welfare of the horse and can manifest in varying ways. Some affected horses are asymptomatic – meaning they show no external signs of ulcers. Other show significant signs of discomfort and agitation.

It is thought that between 60 – 100% of competition horses are affected by EGUS, with the highest prevalence seen in high performing athletes. [1]

EGUS was first described in horses in 1999 and is an umbrella term for the two types of stomach ulcers seen in horses: squamous ulcers and glandular ulcers. [2]

Squamous vs. Glandular

The horse’s stomach is split into two regions: the upper non-glandular squamous region, and the lower glandular region. The fold of tissue that divides these two regions is called the margo plicatus.

The majority of stomach ulcers are found in the upper squamous mucosa region, particularly the greater and lesser curvatures of the stomach.

Ulcers can also be found in the glandular region of the stomach, often around the outflow tract into the small intestine – the pylorus. EGUS can also encompass ulceration of the small intestine immediately exiting the stomach, called the duodenum. [2]

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn - Equine Nutrition Consultants | Mad Barn USA

What Causes Stomach Ulcers in Horses?

Horses continually produce hydrochloric acid (HCl; gastric acid) in their stomach in response to signals, such as histamine and gastrin.

A mature adult horse can produce up to 60 litres (16 gallons) of stomach acid in a single day. Unlike other mammals, horses produce stomach acids whether or not there is food in the stomach.

Gastric acid is produced exclusively by cells located in the glandular region of the stomach. In order to protect itself from constant contact with gastric acid, the glandular mucosa produces a protective barrier of mucus and bicarbonate. The mucus serves as a physical barrier, while bicarbonate buffers acids near the cell surface.

When a horse is exercising, abdominal pressure contracts the stomach and forces acidic gastric juices upwards. These low pH juices splash onto the delicate unprotected squamous mucosa of the stomach, causing erosion of the barrier.

Repeated daily splashing of acidic juices on the sensitive squamous mucosa leads to the formation of lesions, which develop into gastric ulcers. [2]

Squamous ulcers are particularly common in performance horses due to their increased level of exercise. They can also occur more frequently in horses that go long stretches with an empty stomach.

Glandular Ulcers

The cause of glandular ulcers is not as clear, but several factors have been identified as contributing to this condition.

Non-steroidal anti-inflammatories (NSAIDs) are used to alleviate pain associated with injuries and arthritis. Common NSAIDs horse-owners may be familiar with include phenylbutazone “Bute”, Banamine, and Equioxx.

However, these medications reduce gastric circulation and decrease the amount of bicarbonate secreted from glandular mucosa. NSAIDs can also induce oxidative stress in stomach tissue and reduce prostaglandin production in some animals. [21][22][23]

These effects can weaken the protective barrier in the glandular region, enabling acidic gastric juices to damage the mucosa, potentially leading to ulcers.

Helicobacter spp. bacteria, the causative agent of gastric ulcers in humans, have also been considered as a cause of glandular ulcers, but this has not yet been proven. Stress may also contribute to glandular ulceration through the release of the stress hormone cortisol. [3]

High Grain Diets

High grain (carbohydrate) diets also contribute to ulceration in horses. When excess carbohydrates are fermented within the stomach, they lower the pH level making the stomach more acidic.

Fermentation of carbohydrates by bacteria such as Lactobacillus spp. leads to the production of lactic acid and volatile fatty acids (VFAs).

Lactic acid and VFAs damage stomach mucosa by penetrating the squamous epithelial cell lining, making the stomach susceptible to further damage by stomach acid. [4][5]

What are the Symptoms of EGUS?

The clinical signs associated with gastric ulcers are varied and symptom severity does not necessarily correlate to the severity of gastric ulceration.

Some common signs of ulcers include: [6]

  • Mild colic
  • Abdominal discomfort
  • Weight loss
  • Girthiness (dislike to being girthed or having saddle on)
  • Poor appetite
  • Poor performance
  • Behavioural issues such as rearing, bucking, napping, and biting


EGUS is definitively diagnosed by a veterinarian via gastroscopic exam. A gastroscope is a long camera that is passed up the horse’s nostril and down the esophagus and into the stomach.

The stomach is then pumped with air – inflating it and enabling the veterinarian to assess the integrity of both squamous and glandular gastric mucosa. Once the veterinarian has assessed the stomach, the stomach is deflated and the gastroscope is removed.

This routine procedure is done under standing sedation after a period of fasting. Horses are typically fasted for 12-16 hours prior to gastroscopy to enable the veterinarian to have a full view of the stomach.

Gastric ulcers are seen as red or dark lesions on the stomach mucosa. EGUS is graded on a 0-4 scale. Grade 4 ulcers are the most severe and typically consist of widespread, deep, pitted lesions. [6]

While a gastroscope is the only way to confirm the presence of ulcers, many veterinarians will make a diagnosis based on clinical signs and your horse’s history without requiring this expensive procedure. Given the high prevalence of gastric ulcers, horses in heavy work with signs of gut issues are generally presumed to have ulcers.

How to Treat Gastric Ulcers

It’s important to note that treatment for gastric ulcers depends on the type of ulcer present – squamous ulcers are treated differently than glandular ulcers. This is why getting a definitive diagnosis via gastroscope is encouraged.

Speak to your veterinarian to determine an appropriate treatment if your horse has gastric ulcers. Treatment generally involves a combination of medications and changes to nutrition and husbandry management.

The primary treatment for squamous ulcers is omeprazole, while the primary treatment for glandular ulcers is misoprostol. Other medications, like sucralfate, antacids, and histamine-receptor antagonists may also be used or considered for certain cases.

There is also growing interest in effective natural supplements for equine ulcers, which carry a lower risk of side effects and cost less.


Mechanism of Action

Omeprazole is a type of drug known as a proton pump inhibitor (PPI). PPIs work by inhibiting the secretion of gastric acid within the stomach.

They interfere with the function of the gastric parietal cells that produce gastric acids by blocking their proton pumps and damaging their ability to secrete gastric juices.

As a result, omeprazole reduces the level of acidity within the stomach. In other words, it raises the pH of the gastric juice. This gives the gastric mucosa an opportunity to heal and re-build the barrier protecting the stomach lining.

The reduction in gastric acid levels is primarily effective in treating splash ulcers in the squamous region. It is much less effective for treating glandular ulcers. [2]


Omeprazole is typically administered to horses in 37% GastroGard paste form at a dose of 4 mg per kilogram bodyweight per day. Oral omeprazole should be given 1 hour before food to ensure that as much of the drug as possible comes into contact with the stomach lining. [10]

For a standard adult horse of 500 kg (1100 lb), this is 2000 mg of Omeprazole per day which is equivalent to one syringe of GastroGard paste per day.

Lower doses of 1.6 mg per kilogram bodyweight per day have been shown effective at reducing gastric acid production and ulceration severity. However, this dosage is not as consistent at promoting ulceration healing compared to the 4 mg dose. [8]

A 1 mg dose of omeprazole is 82% effective at preventing ulcer re-occurrence and the 2 mg dose is 89% effective during stressful situations or when the horse is in hard work. [10]

For squamous ulcers, omeprazole is typically administered for 28 days to enable full healing. Research shows that 86% of horses’ ulcers are healed within 28 days.

For glandular ulcers, omeprazole is typically administered for longer periods. It may also be administered alongside antimicrobials and gastroprotective supplements, such as sucralfate. [8][9][10]

Side Effects

Use of omeprazole can result in a decrease in protein metabolism as well as calcium and magnesium absorption. [15][16][17]

Omeprazole has also been found to alter the microbes in the stomach, but more research is needed to understand the significance of this. [18][19]

However, these side effects are minimal if omeprazole is dosed appropriately under the direction of a veterinarian.


Misoprostol is a synthetic prostaglandin, which is a type of immune compound that inhibits acid secretion and stimulates mucous secretion in the glandular stomach.

As a prostaglandin analogue, misoprostol may improve glandular mucus barrier function and integrity.

Research shows that horses treated with misoprostol exhibit increased mucous and bicarbonate production. Additionally, misoprostol has shown anti-inflammatory effects. [26]

One clinical trial in horses with glandular ulcers showed that misoprostol treatment was more effective than omeprazole. [27]


Sucralfate is a mucosal protectant. It forms a physical barrier to protect the gastric mucousa against degradation by gastric acids and also increases blood flow to the area. This helps facilitate ulcer healing and decreases pain associated with ulcers. [24] [28]

Administration of sucralfate in horses also improves the secretion of mucous and bicarbonate. This can provide further protection for the stomach lining.

Sucralfate is often administered alongside other treatment options such as omeprazole to increase its efficacy. Timing of administration and your horse’s feeding schedule needs to be carefully managed so as to not impair absorption. [2]

H-2R Antagonists

H-2R antagonists, such as ranitidine hydrochloride, are used to increase gastric pH in both humans and horses.

These drugs block the action of histamine, which is a hormone that stimulates the production of stomach acid from parietal cells. Like omeprazole, H-2R antagonists make the stomach less acidic and help ulcers heal.

Ranitidine hydrochloride is typically administered three times per day, which makes it less convenient for many horse-owners. Additionally, while it has been shown to reduce stomach ulceration in horses [25], it is overall less effective than omeprazole. [29]

Aloe Vera

Aloe vera has been found to help treat gastric ulcers in humans and rats. This medicinal plant has anti-inflammatory and anti-oxidative properties. [12][13]

In a trial, 40 horses with squamous and/or glandular EGUS lesions (> grade 2) were administered omeprazole or dried inner leaf aloe vera.

Horses given aloe vera showed a 56% improvement in lesion severity, however only 17% of lesions were completely healed after 28 days supplemented with aloe vera.

The improvement in lesion severity in horses treated with omeprazole was 85%, with a 75% healing rate after 28 days. [14]

This suggests that while aloe vera can aid in the treatment of gastric ulcers, its efficacy is not comparable to omeprazole.

Visceral+ for Gut Health

A number of natural ingredients have been found effective for supporting the natural barrier that protects the stomach lining from gastric acids.

Mad Barn’s Visceral+ is formulated to help horses maintain healthy stomach tissue, hindgut health and immune function.


5 stars
4 stars
3 stars
2 stars
1 star

Learn More

  • Our best-selling supplement
  • Maintain stomach & hindgut health
  • Supports the immune system
  • 100% safe & natural

Nutritional Management of Gastric Ulcers

Nutritional management of horses with stomach ulcers is critical. Without the correct nutritional management, treating gastric ulcers is challenging and the chance of re-occurrence high.

As trickle feeders, horses are designed to graze almost continuously throughout the day. Feral horses spend around 16 hours out of their day grazing.

Stabled horses are typically only fed twice daily, often going long periods between meals without forage.

However, research shows that horses that go more than 6 hours without forage have a four-fold increase in the likelihood of developing gastric ulcers. [20]

Horses produce stomach acid constantly, even when there is no food to digest within the stomach. Moreover, when horses are exercised on an empty stomach, gastric juices splash onto sensitive squamous mucosa potentially leading to ulcers. [10]

The best thing you can do to reduce your horse’s ulcer risk is to always provide them with access to forage and never exercise them on an empty stomach.

Feeding Plan for Ulcer Recovery

Grain (carbohydrates) should be avoided for horses with or prone to gastric ulceration. Carbohydrates are fermented to some extent within the stomach, disrupting the microbiome and releasing lactic acid and VFAs. [5]

Instead, horses with ulcers should be fed a forage-first diet that supports gut health and prolongs feeding time. Consider the following strategies: [5][10]

  • Provide continuous access to forage and avoid intermittent feeding or long periods of time between meals. The prevalence of ulcers in horses fed twice daily is 75% compared to 58% for horses fed three times daily.
  • Feed alfalfa prior to exercising; this legume hay has high calcium content and can help to buffer stomach acid.
  • Feed oil (such as flax/linseed oil or W-3 oil) as an energy source instead of grain-based concentrates.
  • Feed Visceral+ to support gastric health and immune function
  • Give your horse constant access to fresh water. Horses that do not have contact access to water are 2.5 times more likely to develop ulcers. [20]

Management Practices

In addition to nutritional changes and omeprazole treatment, the following husbandry management practices should be considered. [10]

  • Keep your horse on grass pasture and provide regular turnout. Stabling increases ulcer risk because it increases stress and alters eating habits.
  • Fed a handful of soft fibre one hour before exercise to help prevent gastric juices from being able to splash up onto sensitive squamous mucosa.
  • While your horse is being treated for ulcers, retire them to pasture or limit them to light work. Intense exercise increases the risk of squamous ulcers.
  • Find ways to reduce your horse’s stress levels. Stress leads to higher levels of the hormone cortisol, which is a contributing factor to glandular ulcers. Some strategies to reduce stress include:
    • Provide plenty of turnout in a social group
    • Wean foals together onto pasture
    • Minimize travelling or trailering
    • Hang mirrors in stables
    • Consider enrichment activities to combat boredom


In summary, there are two types of gastric ulcers that affect horses: squamous and glandular.

Squamous ulcers are more common, typically caused by splashing of gastric acid onto the sensitive non-glandular stomach region. Glandular ulcers are less common, their cause is not well understood and they are harder to treat.

Squamous ulcers and glandular ulcers are treated differently, which is why it is important to pursue a definitive diagnosis with your veterinarian. Omeprazole is most effective for treating squamous ulcers, while misoprostol is most effective for glandular ulcers.

Mad Barn’s Visceral+ is a pelleted supplement that can be fed to support gut health in horses coming off of omeprazole treatment.


5 stars
4 stars
3 stars
2 stars
1 star

Learn More

  • Our best-selling supplement
  • Maintain stomach & hindgut health
  • Supports the immune system
  • 100% safe & natural

Is Your Horse's Diet Missing Anything?

Identify gaps in your horse's nutrition program to optimize their well-being.


  1. Bell, R.J.W., Mogg, T.D. and Kingston, J.K. Equine gastric ulcer syndrome in adult horses: a review. New Zealand veterinary journal. 2007. View Summary
  2. Sykes, B. W. et al. European College of Equine Internal Medicine Consensus Statement–Equine Gastric Ulcer Syndrome in Adult Horses. Journal of veterinary internal medicine. 2015. View Summary
  3. Malmkvist, J. et al. Behaviour and stress responses in horses with gastric ulceration. Applied animal behaviour science. 2012.
  4. Andrews, F.M. et al. Gastric ulcers in horses. Journal of Animal Science. 2005.
  5. Nadeau, J.A. et al. Evaluation of diet as a cause of gastric ulcers in horses. American journal of veterinary research. 2000. View Summary
  6. Nieto, J.E. et al. Prevalence of gastric ulcers in endurance horses–a preliminary report. The Veterinary Journal. 2004.View Summary
  7. Richardson, P., Hawkey, C.J. and Stack, W.A. Proton pump inhibitors. Drugs. 1998.
  8. Sykes, B.W., Sykes, K.M. and Hallowell, G.D. A comparison of two doses of omeprazole in the treatment of equine gastric ulcer syndrome: a blinded, randomised, clinical trial. Equine veterinary journal. 2014.View Summary
  9. Al Jassim, R. et al. Gastric Ulceration in Horses The role of bacteria and lactic acid. 2008.
  10. Hepburn, R. Gastric ulceration in horses. In Practice. 2011.
  11. Andrews, F.M. et al. Effects of intravenously administrated omeprazole on gastric juice pH and gastric ulcer scores in adult horses. Journal of veterinary internal medicine. 2006. View Summary
  12. Borrelli, F. and Izzo, A.A. The plant kingdom as a source of anti-ulcer remedies. Phytotherapy Research: An International Journal Devoted to Pharmacological and Toxicological Evaluation of Natural Product Derivatives. 2000.
  13. Borra, S.K., Lagisetty, R.K. and Mallela, G.R. Anti-ulcer effect of Aloe vera in non-steroidal anti-inflammatory drug induced peptic ulcers in rats. African Journal of Pharmacy and Pharmacology. 2011.
  14. Bush, J., Van Den Boom, R. and Franklin, S. Comparison of aloe vera and omeprazole in the treatment of equine gastric ulcer syndrome. Equine veterinary journal. 2018. View Summary
  15. Pagan J.D. et al. Omeprazole reduces calcium digestibility in Thoroughbred horses. J Equine Vet Sci. 2020. View Summary
  16. Melo S.K.M. et al. A proton-pump inhibitor modifies the concentration of digestion biomarkers in healthy horses. J Equine Vet Sci. 2014.
  17. Thongon N. & Krishnamra N. Omeprazole decreases magnesium transport across Caco-2 monolayers. World J Gastroenterol. 2011.
  18. Tyma J.F. et al. Investigation of effects of omeprazole on the fecal and gastric microbiota of healthy adult horses. Am J Vet Res. 2019. View Summary
  19. Cerri S. et al. Effect of oral administration of omeprazole on the microbiota od the gastric glandular mucosa and feces of healthy horses. J Vet Intern Med. 2020View Summary
  20. Luthersson, N. et al. Risk factors associated with equine gastric ulceration syndrome (EGUS) in 201 horses in Denmark. Equine Vet J. 2009.View Summary
  21. Matsui, H. et al. The pathophysiology of non-steroidal anti-inflammatory drug (NSAID)-induced mucosal injuries in stomach and small intestine. J Clin Biochem Nutr. 2011.
  22. Martinez Aranzales, J.R. et al. Orally administered phenylbutazone causes oxidative stress in the equine gastric mucosa. J Vet Pharmacol Ther. 2015. View Summary
  23. Pedersen, S.K. et al. Phenylbutazone induces equine glandular gastric disease without decreasing prostaglandin E2 concentrations. J Vet Pharmacol Ther. 2017. View Summary
  24. Bishop, R.C. et al. Effect of omeprazole and sucralfate on gastrointestinal injury in a fasting/NSAID model. Equine Vet J. 2021.View Summary
  25. Furr, M.O. and Murray, M.J. Treatment of gastric ulcers in horses with histamine type 2 receptor antagonists. Equine Vet J. 1989. View Summary
  26. Wallace J.L. Prostaglandins, NSAIDs, and gastric mucosal protection: why doesn’t the stomach digest itself?. Physiol Rev. 2008.
  27. Varely G. et al. Misoprostol is superior to combined omeprazole-sucralfate for the treatment of equine gastric glandular disease. Equine Vet J. 2019. View Summary
  28. Rees W.D. Mechanisms of gastroduodenal protection by sucralfate. Am J Med. 1991.
  29. Lester G.D. et al. Effects of treatment with omeprazole or ranitidine on gastric squamous ulceration in racing Thoroughbreds. J Am Vet Med Assoc. 2005. View Summary