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.

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]

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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]