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 this barrier. Intermittent feeding, high-intensity exercise, stress and certain drugs can contribute to the development of gastric ulcers.

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. However, many horses experience a relapse when weaning off of Omeprazole. But there are steps you can take to prevent ulcers from returning.

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


Quiz: Assess Your Horse's Ulcer Risk

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 adult horses are affected by EGUS, with the highest prevalence seen in performance horses. [1]

EGUS was first described in horses in 1999 and is an umbrella term for the two types of stomach ulcers seen in horses: Equine glandular gastric disease (EGGD) and Equine squamous gastric disease (ESGD). [2]

Squamous vs. Glandular

The horse’s stomach is split into two regions: the upper non-glandular squamous mucosa, and the lower glandular mucosa. The dividing line between the two regions is known as the margo plicatus line.

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 fundic region of the stomach, and in the glandular pyloric region. EGUS can also consist of duodenal ulceration within the small intestine. [2]

What Causes Stomach Ulcers in Horses?

Horses continually produce hydrochloric acid (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 acids are normally found in the lower glandular region of the stomach, which produces mucous and bicarbonate to form a barrier that protects the stomach lining.

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]

These so-called “splash ulcers” are common in performance horses. Splash ulcers generally occur during exercise, particularly when the stomach is empty.

Glandular Ulcers

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

Non-steroidal anti-inflammatories (NSAIDs) – such as Phenylbutazone – are used to alleviate pain associated with injuries and arthritis.

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

Helicobacter spp. bacteria 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 clinically diagnosed by a veterinarian using a gastroscope. 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 using the gastroscope camera. Once the veterinarian has assessed the stomach, the gastroscope is removed.

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, where 0 is no ulceration present, 1 is the beginning of lesion development and >2 indicates clinically significant lesions.

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

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 EGUS is a drug known as omeprazole (GastroGard, UlcerGard). This is the only FDA-approved anti-ulcer drug available and many performance horses are maintained on it year-round to prevent ulcers.

Other medications used to treat ulcers include sucralfate (Carafate), antacids, and histamine-receptor antagonists. There is also growing interest in effective natural supplements for equine ulcers, which carry a lower risk of side effects and cost less.

What is Omeprazole?

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.

The proton pump of the gastric parietal cell is blocked by stopping the hydrogen-potassium adenosine triphosphatase enzyme system of the cell.

These cells constantly die off and are replaced. Thus, omeprazole needs to be given continuously to maintain a reduction in gastic pH.

Omeprazole is metabolized in the liver and excreted within the urine. [7]

How does Omeprazole Work?

As a PPI, omeprazole reduces the level of acidity within the stomach. 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, but omeprazole has also been successful in healing or reducing the severity of glandular ulcers. [8]

Some oral omeprazole treatments are given in an alkaline medium to help neutralize stomach acidity.

A repeat gastroscopy is typically undertaken after 28 days of omeprazole administration to assess whether your horse’s gastric ulcers have fully healed.

What Dose of Omeprazole should my Horse have?

Omeprazole is typically administered to horses in 37% GastroGard paste form at a dose of 4 mg per kilogram bodyweight per day.

For a standard adult horse of 500 kg (1100 lb), this is 2000 mg of Omeprazole per day which is roughly 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]

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]

How do I give my horse Omeprazole?

Omeprazole is typically administered to horses orally, in a dosing syringe. This medication should be administered daily.

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]

Omeprazole can also be administered via a weekly injection into the muscle for horses that struggle to take the drug orally. [11]

Omeprazole 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]

Use of omeprazole is not recommended in pregnant or lactating mares. This drug should be used with caution in horses with liver problems and in horses on anticoagulant medications such as warfarin.

Omeprazole for Preventing Ulcer Re-occurrence

Omeprazole is not a cheap medication and many horse owners are keen to get their equine companions off of this drug as soon as possible.

However, due to a phenomenon known as rebound acid hypersecretion (RAHS), there is a high rate of ulcer recurrence after cessation of proton-pump inhibitor treatment.

RAHS is characterized by a temporary increase in stomach acid as a result of compensatory mechanisms that are triggered by the use of Omeprazole. This increased secretion of gastric juices often leads to new ulcers being formed.

To prevent this, many horses are kept on a preventative dose of omeprazole at 1-2 mg per kilogram bodyweight per day. UlcerGard is a non-prescription (over-the-counter) product that contains a lower dose of omeprazole compared to GastroGard.

UlcerGard is also used preventatively during stressful situations, such as travelling or moving stable yards.

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]

Visceral+ for Gut Health

Omeprazole works because it prevents parietal cells from secreting gastric acid.

Omeprazole does not directly promote healing of gastric ulcers or re-building of the gastrointestinal barrier. Instead, it works by fighting against the horse’s natural biology to increase gastric pH and give ulcers an opportunity to heal.

But this is not the only way to address ulcers. 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 with safe, natural ingredients to help horses maintain healthy stomach tissue, digestion and immune function.

Visceral+ was designed in conjunction with veterinarians who were tired of treating horses with omeprazole only to have near-universal ulcer recurrence after stopping treatment.

Visceral+ is clinically tested and shown to work in horses coming off of omeprazole treatment.

Visceral+ Ulcer Supplement for Horses


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Sucralfate for Glandular Ulcers

Sucralfate (Carafate) is a drug commonly used to treat ulcers in foals. It is also administered alongside omeprazole to enhance the healing of glandular ulcers.

Sucralfate is typically given orally at a dose of 20 mg per kilogram bodyweight every 12 hours. This drug works by reacting with stomach acid to form a paste that binds to the sites of ulcers on the stomach wall.

The medication adheres to protein-containing secretions that are released by gastric lesions, providing a physical barrier to protect the ulcer from stomach acid as it heals.

Sucralfate also helps increase blood flow to the area, which supports healing processes. [24]

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 at a dose of 6.6 mg per kilogram bodyweight every eight hours. Ranitidine hydrochloride treatment has been shown to reduce stomach ulceration in horses. [25]

However, ranitidine requires three doses to be administered every 24 hours. Owner compliance is poor with this drug, and so omeprazole remains the drug of choice when treating stomach ulcers. [25]


Antibiotics may be used as part of a treatment plan alongside omeprazole if squamous ulcers have not healed following an initial 28-day course. [10]

Trimethoprim sulfadiazine has been shown to aid in the healing of squamous ulcers over 4-6 weeks. This drug is given orally at a dose of 15 mg per kilogram bodyweight every 12 hours.

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.

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 reduce the likelihood of ulcers recurring after treatment. Visceral+ is formulated with natural ingredients that support gastric barrier 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 fullowing 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 splash 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.

Oral omeprazole (GastroGard) is a proton pump inhibitor that is the only FDA licensed drug for treating gastric ulcers in horses. It works by inhibiting the production of gastric acid in the stomach.

Low-dose omeprazole is sometimes given to horses in hard work or stressful environments to help prevent ulcer reoccurrence. However, changes to feeding and management practices are necessary to ensure ulcers do not return after stopping omeprazole.

Mad Barn’s Visceral+ is a natural supplement that can be fed to support gut health in horses coming off of omeprazole treatment. It is clinically tested in horses with ulcers and has been shown to work.

Visceral+ Ulcer Supplement for Horses


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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

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  3. Malmkvist, J. et al. Behaviour and stress responses in horses with gastric ulceration. Applied animal behaviour science. 2012.
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  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.
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  23. Pedersen, S.K. et al. Phenylbutazone induces equine glandular gastric disease without decreasing prostaglandin E2 concentrations. J Vet Pharmacol Ther. 2017.
  24. Bischop, R.C. et al. Effect of omeprazole and sucralfate on gastrointestinal injury in a fasting/NSAID model. Equine Vet J. 2021 .
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