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Diagnosing and Treating Gastric Ulcers in Horses

What you need to know about glandular and squamous gastric diseases in horses

By: Stacey Oke, DVM, MSc

Sponsored By:

PHOTO: Kevin Thompson/The Horse

Equine gastric ulcer syndrome, or EGUS, is an umbrella term that refers to ulceration of the gastric mucosa, which lines the inside of the horse’s stomach. It affects a substantial number of racing, performance, pasture, and even feral horses. In fact, no horse is “safe” from EGUS. Despite EGUS being a catchall phrase for any lesion occurring in the stomach, it actually takes two distinct forms: squamous and glandular disease. Horses can suffer from either, and some horses develop both types of gastric disease simultaneously.

“Squamous and glandular gastric disease are two entirely different diseases that just happen to affect the stomach,” says Dr. Sara Busechian, formerly of the University of Perugia’s Department of Veterinary Medicine, in Italy.

Sara Busechian, DVM, PhD, MRCVS, Dipl. ECEIM,

graduated from the University of Perugia’s Department of Veterinary Medicine in 2007, followed by a PhD in Equine Sciences in 2011. She spent her postdoctoral years from 2013 to 2022 at the University of Perugia focusing on equine internal medicine and equine gastric ulcer syndrome. A Diplomate of the European College of Equine Internal Medicine since 2022, Busechian now works as a private practitioner.

Gastric Ulcer Occurrence in Various Horse Populations

Categories for which research data are available. Source: Vokes et al., 2023

In this feature we’ll review the anatomy of the horse’s stomach and describe risk factors, prevention, and treatment for both glandular and squamous disease.

ILLUSTRATION: Dr. Robin Peterson / Zuzule photo/The Horse

The Basics of the Equine Stomach

While the equine gastrointestinal tract is very large, the stomach itself is remarkably tiny, having a capacity of only 2-5 gallons (18 liters). The equine stomach is divided into two distinct regions: the upper (dorsal) and the lower (ventral). A ridge of tissue called the margo plicatus separates the two sections. In the dorsal region, above the margo plicatus, the stomach is lined with squamous mucosa—a thick layer of skinlike cells. The squamous region of the stomach has no absorptive capacity or secretory activity. Thus, it produces no enzymes or acid to digest feeds and absorbs no nutrients. Food simply passes through this region on its way from the esophagus to the glandular (ventral) region of the stomach, located below the margo plicatus, before flowing into the small intestine. In the ventral region of the stomach, cells in the glandular mucosa produce mucous as well as hydrochloric acid. It is here the digestive process truly begins when feed mixes with the gastric juices that fill the glandular region of the stomach.

That layer of “slime” containing mucus and bicarbonate coats the glandular region of the stomach, protecting it from the gastric juices it produces. The pH of the gastric juice in the glandular stomach is, on average, about 2.9—so acidic that if it touched the skin on your hands, it would burn. The slime layer, however, has a pH of about 7.

When horses graze and consume roughage, such as grass hay or alfalfa hay, the fibers form a sort of mat that floats on the surface of the gastric juice around the level of the margo plicatus. This, along with saliva, helps buffer the pH of the fluid touching the squamous mucosa. The acidic gastric juice from the glandular region of the stomach, however, can splash up onto the unprotected squamous region when the horse exercises or if that fibrous mat is not present on the surface of the gastric contents (e.g., the horse is fasted).

PHOTO: Anne M. Eberhardt/The Horse

The Foundations of Glandular Gastric Disease in Horses

While we know gastric acid touching the squamous mucosa causes ulcers, we know much less about what causes lesions of the glandular mucosa.

“We often state that glandular disease results when the natural defense mechanisms of the stomach are compromised,” says Dr. Robin van den Boom, an associate professor in the Department of Clinical Sciences at Utrecht University, in the Netherlands. “These mechanisms include the production of the protective mucous layer, and this seems to be dependent on normal blood flow, which in turn is mediated by mediators called prostaglandins.

“There is mounting evidence that stress contributes to glandular disease, but we don’t know (very well) what causes this type of stress,” he adds. “Certainly, exercise can cause physiological stress.”

Robin van den Boom, DVM, PhD, Dipl. ECEIM,

graduated from Utrecht University, in the Netherlands, in 1996 and started his training in equine surgery. He served as head of the Department of Equine Health at the University of Adelaide (Australia) from 2014 to 2017, when he returned to the Netherlands where he’s currently head of the Equine Medicine team at Utrecht University. His clinical and research interests include the equine gastrointestinal tract and dermatology.

Risk Factors for Glandular Ulcers

The main risk factor for glandular disease is exercise frequency, with horses exercising five or more times per week having a greater risk of ulcers developing in the glandular mucosa.

Further, data from Warmblood show jumpers show that increased days in work and actively competing increase the risk of glandular disease. For endurance horses the risk of glandular disease doubles during the competition season compared with the interseason period (Vokes et al., 2023).

Gastroscopic image of the pylorus of a 10-year-old Warmblood gelding with glandular disease. PHOTO: Courtesy Dr. Mike Hewetson

A second important risk factor is the number of trainers, handlers, or riders a horse has. The more people working with the horse, the greater his risk of having glandular ulcers.

“This emphasizes the importance of the horse-human interaction or bond and the need for predictable routines to help minimize the horse’s stress level,” says van den Boom.

Although nutritional risk factors are major contributors to squamous disease (discussed later on), they’re not as important for glandular disease.

Glandular Ulcer Prevention

In addition to ensuring horses have rest days so as not to exceed five days of exercise per week, controlling behavioral stress through environmental enrichment might help prevent glandular gastric disease (Vokes et al., 2023). This might include relaxation tactics such as soothing music and massage.

For instance, researchers have found that playing classical music caused horses to be less alert and ingest feed more frequently (Huo et al., 2021) and that massage reduces horses’ stress levels (Kędzierski et al., 2017).

Relaxing strategies such as massage might help reduce horses’ ulcer-inducing stress levels. PHOTO: Getty Images

Both music and massage therapy are easy to implement into a horse’s daily routine.

“I also believe that herd composition and probably size of the pen/paddock/pasture also play a role in glandular disease in terms of stress,” adds van den Boom.

Glandular Ulcer Treatment in Horses

Pharmacologic therapies for glandular disease include omeprazole, sucralfate, and, to a lesser extent, misoprostol. Omeprazole is a proton pump inhibitor that decreases hydrochloric acid secretion by the parietal cells in the glandular mucosa. Acid suppression is the cornerstone of treating EGUS in horses, be it glandular or squamous disease.

Despite omeprazole being considered a mainstay in pharmacologic management of EGUS, Varley et al. (2019) state that omeprazole given alone for glandular disease is “largely ineffective,” especially when compared to the response seen in horses with squamous disease.

Dr. Tania Sundra, of Avon Ridge Equine Veterinary Services, in Western Australia, says from the studies published to date, less than 50% of glandular lesions heal with omeprazole monotherapy. Further, treatment duration is also longer than for squamous disease.

“The current recommended dose of omeprazole for treating glandular disease is 4 mg/kg by mouth once daily in conjunction with 12 mg/kg of sucralfate by mouth twice daily,” says Busechian.

Sucralfate is a compound that has many proposed mechanisms of action, including creating a physical barrier that blocks acid diffusion from the lumen of the stomach to the mucosa.

“It also has the ability to stimulate bicarbonate production in the stomach, buffering the acid produced by the stomach,” she adds.

“If also giving sucralfate for glandular disease, omeprazole should be given first, wait 30 minutes, then give sucralfate, wait 30 minutes, and then feed,”

As an alternative to a combination of omeprazole and sucralfate, Varley et al. explored the efficacy of misoprostol in 63 horses with glandular disease greater than Grade 1 out of 4 and found the drug was superior to the omeprazole-sucralfate combination for glandular lesion improvement and healing. Misoprostol is a prostaglandin E1 analog that has multiple proposed mechanisms, including improving blood flow to the glandular mucosa and enhancing mucosal resistance to injury.

“If also giving sucralfate for glandular disease, omeprazole should be given first, wait 30 minutes, then give sucralfate, wait 30 minutes, and then feed,”

—Dr. Sarah Reuss


Still, omeprazole remains the treatment of choice for glandular disease. “I think omeprazole is used more often because omeprazole is FDA-approved for horses while misoprostol is not,” says Busechian. “Misoprostol has more side effects than sucralfate and omeprazole.”

“In addition to misoprostol not being registered for horses, evidence supporting its use for glandular disease is lacking,” adds Sundra. “Some reports also show an exacerbation of squamous disease when misoprostol has been used. As well, there are human health concerns associated with misoprostol, namely abortion.”

In summary, little is known about how glandular disease develops or how to best treat it, but we do know stresses related to exercise and handling can exacerbate it. “In addition to glandular disease being difficult to treat, especially compared with squamous disease, we also have some indications (in unpublished data) that the healing of glandular disease is further compromised by the presence of inflammatory bowel disease (IBD),” says van den Boom.


Omeprazole: A proton pump inhibitor that decreases hydrochloric acid secretion by the parietal cells in the glandular mucosa.

Sucralfate: A compound that physically blocks acid diffusion from the lumen of the stomach to the mucosa and stimulates acid-buffering bicarbonate production in the stomach.

Misoprostol: A prostaglandin E1 analog that has multiple proposed mechanisms, including improving blood flow to the glandular mucosa and enhancing mucosal resistance to injury.

Tania Sundra, BSc (Hons), BVMS, MANZCS (Equine Medicine),

graduated from Murdoch University, in Perth, Australia, in 2009 and completed an equine internship at a busy performance horse hospital in the United States. Upon returning home she spent a few years working in racetrack and repro clinics in Western Australia. In 2015 Sundra founded Avon Ridge Equine Veterinary Services, an ambulatory equine practice servicing Perth and surrounding regions. She has a keen interest in all things related to equine medicine and is actively involved in clinical research.

Sarah Reuss, VMD, Dipl. ACVIM,

serves as an equine technical manager with Boehringer Ingelheim Animal Health. She was a clinical assistant professor and chief of the Large Animal Medicine Service at the University of Florida’s College of Veterinary Medicine until transitioning to industry in 2016. Her professional interests include equine gastrointestinal disease, neurology, endocrine disease, respiratory disease, and infectious diseases. She is active in organized veterinary medicine, currently serving as chair of the AAEP’s Horse Owner Education committee, in addition to roles in the ACVIM, AVMA, and Veterinary Leadership Institute. Recently, she has been appointed 2024 vice president of the AAEP; she will serve as the organization’s president in 2026.

PHOTO: Getty Images

All About Squamous Disease in Horses


As we noted earlier, gastric acid contacting and damaging the mucosa is the most common cause of ulcers in the squamous region of the stomach. Major risk factors for squamous ulceration include the absence of a “splash guard” due to lack of roughage intake or prolonged periods of fasting. In general, horses should consume 2% of their body weight in forage per day.“Continuous access to forage is ideal for horses but sometimes difficult to achieve practically,” says van den Boom. “I recommend the use of haynets, or sometimes even double haynets or other slow feeder devices, to keep the periods without roughage as short as possible.”

Other Squamous Ulcer Risk Factors in Horses

Van den Boom says the following dietary and husbandry practices can also contribute to the development of squamous ulcers:

PHOTOS: Getty Images

Preventing Squamous Ulcers in Horses

Based on the above risk factors, van den Boom’s top two recommendations for preventing squamous disease are providing a diet with good-quality forage and a predictable daily routine (without too much stress).

Squamous Ulcer Treatment

Squamous ulcers will not heal unless you and your veterinarian identify the risk factors and correct them via altered management practices, such as offering more roughage and minimizing concentrated feeds.

And just like for glandular disease, acid suppression is the first step in treating squamous ulcers. In the United States, omeprazole is labeled at 4 mg/kg for 28 days for the treatment of EGUS in horses and foals older than 4 weeks of age.

Busechian advises giving omeprazole in the morning, at least 30 minutes before a forage meal.

“Omeprazole has good success in healing squamous ulcers, with about over 70% resolving within four to five weeks of initiating omeprazole monotherapy,”
—Dr. Tania Sundra

Adds Sundra, “Omeprazole has good success in healing squamous ulcers, with about over 70% resolving within four to five weeks of initiating omeprazole monotherapy.”

Veterinarians do not currently recommend sucralfate for treating squamous disease unless the horse also suffers from glandular disease, says Busechian.

“The pathophysiology of the two diseases is different, and squamous disease responds well to only omeprazole,” she explains. “Misoprostol, again, is not needed in squamous disease because misoprostol works by improving blood flow to the mucosa. Impaired mucosal blood flow is one of the proposed mechanisms of formation of glandular disease, not squamous.”

So again, unlike glandular disease, managing diet is the main way of preventing EGUS due to squamous disease.

PHOTO: Courtesy Christina Weese/

Diagnosing EGUS: Endoscopy Is the First Essential Step

“Signs that a horse owner or veterinarian might observe in a horse with EGUS, due to either glandular or squamous disease, can vary,” says Reuss. “Most commonly, horses show a decline in performance.”

In addition to poor(er) performance, Reuss says other indications of EGUS might include:

  • An unwillingness to work.
  • Reluctance to bend or flex.
  • Bucking/bolting/rearing.
  • A decline in objective performance measures, such as an uptick in speed or jumping faults.
  • A crabby attitude, aggression, or displeasure toward being groomed or saddled.
  • Mild signs of colic (abdominal pain), especially after eating a grain meal.
  • Weight loss or inappetence, picky eating.
  • Poor coat condition.
  • Bruxism (teeth grinding).

Owners or trainers might be eager to jump on the gastric ulcer train when they see some of these signs widely attributed to horses with EGUS; however, only a variable level of evidence supports the association between these clinical signs and EGUS. Additionally, whether glandular and squamous disease truly present similarly—as this list implies—also remains unclear. For this reason, the current recommendation has not swayed from that of the European College of Internal Medicine Consensus Statement—Equine Gastric Ulcer Syndromes in Adult Horses, in that EGUS cannot be diagnosed based on “characteristic” clinical signs and should be confirmed via gastroscopy.

Signs of EGUS include a decline in performance, mild colic, a crabby attitude, and teeth grinding, among others. PHOTO:Getty Images

“If a horse has known risk factors, such as trailering or competition, and is showing signs such as a change in performance or mild colic, it is prudent to pursue gastroscopy,” says Reuss. “Just like you would pursue radiographs or ultrasound to better characterize a lameness, scoping the stomach to determine the location and severity of ulcers helps us to best treat that horse.”

Endoscopy is the only reliable way to diagnose EGUS, be it squamous or glandular lesions.

Depending on your veterinarian’s preferences, gastroscopy can be performed either on the farm or in a clinic. You’ll need to fast the horse for approximately 14 to 16 hours, but he can have water up until two to four hours prior to the procedure.

“It is important that the stomach is empty so that all parts can be seen,” Reuss explains. “In most cases this is easier to enforce overnight with the procedure happening first thing in the morning.”

The veterinarian then sedates the horse to approximately the same degree as for a dental procedure and passes the scope through the horse’s nostril and down the esophagus to the stomach. He or she should fully evaluate both the squamous and glandular linings, including the pylorus, which is the opening to the small intestine.

“The entire process takes less than an hour,” Reuss says.

When scoping a horse, veterinarians use the well-described scale of 0 to 4 for equine squamous gastric disease, with 0 being normal and 4 having large or deep bleeding ulcers.

There is currently no agreed-upon scale for glandular ulcers. Instead, veterinarians describe lesions in the glandular region of the stomach based on anatomic location, distribution, severity, and appearance (i.e., hyperemic/hemorrhagic, erosive/ulcerative, fibrinosuppurative, depressed/flat/raised).

“Glandular ulcers can vary from looking like a bruise or blood clot to appearing more like a wound with proud flesh,” says Reuss. “There is ongoing research to determine if these are due to different causes as well as if they will respond differently to treatment.”

She adds that there is no correlation between the severity of the horse’s clinical signs and the grade of ulcers seen in the stomach. Gastroscopy findings dictate how long the horse will be treated with omeprazole and whether he should receive additional drugs, such as sucralfate.

“Going back to the lameness and X ray or ultrasound analogy, think of the stomach similarly,” says Reuss. “When we see signs of EGUS, we look deeper to make a definitive diagnosis, and then we tailor the treatment to the diagnosis. And just like you would recheck the ultrasound of a tendon before putting the horse back to work, we should rescope the stomach at the end of treatment to be sure it has resolved as expected.”

“It is way more frustrating to spend hundreds or thousands of dollars treating an ulcer that was never there to begin with versus pursuing gastroscopy early and knowing exactly what you are treating,”
—Dr. Sarah Reuss

Owners might have cost-related concerns associated with gastroscopy, and our sources all agree that costs associated with diagnosing, treating, and preventing disease recurrence can indeed be substantial. However, establishing an accurate diagnosis from the beginning can help keep long-term costs down.

“It is way more frustrating to spend hundreds or thousands of dollars treating an ulcer that was never there to begin with versus pursuing gastroscopy early and knowing exactly what you are treating,” says Reuss.

PHOTO: Getty Images

Stomach Supplements for Ulcers in Horses

Currently, only a small handful of the many supplements marketed to prevent gastric ulcers in horses are supported by scientific studies:

  • In a population of Thoroughbred racehorses, a combination of apolectol—a pectin-lecithin complex—Saccharomyces cerevisiae, and the buffer magnesium hydroxide appeared to be an effective prophylactic (preventive) against EGUS development or exacerbation (Sykes et al., 2014).
  • A commercially available pelleted supplement containing sea buckthorn berry, L-glutamine, pectin, and lecithin helped reduce recurrence of squamous lesions in horses after omeprazole treatment (Andrews et al., 2015).
  • Corn oil has been shown to decrease gastric acid output (Cargile et al., 2004).
  • Supplementing fit Thoroughbred horses in training with long-chain polyunsaturated fatty acids (a blend of gamma-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid) was positively associated with prevention or resolution of severe squamous ulceration (Pagan et al., 2022).

Bear in mind that nutritional supplements do not have to go through the same approval process as FDA-approved drugs. Always look for supplements supported by published research to back up their claims rather than testimonials.

PHOTO: Getty Images

Concluding Thoughts

Regardless of whether we’re dealing with squamous ulcers, glandular ulcers, or both, preventing EGUS is the best medicine.

“For glandular disease, focus on the horse itself, ensuring adequate rest days are offered and routine, consistent care is provided by the same small number of people,” says van den Boom. “In addition, focus on the horse’s management—diet and housing—to prevent squamous disease.”

Omeprazole—specifically the FDA-approved, shelf-stable form, GastroGard®—is the mainstay for treating squamous ulcers. Although highly effective for that purpose, the response to omeprazole alone for horses with glandular disease might be underwhelming, which is why it is so important for veterinarians to scope and see where the lesions are located. Finally, gastric disease is likely to recur unless you address the risk factors.

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Stacey Oke, MS, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005 she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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