Equine Gastric Ulcer Syndrome (EGUS)

Gastric Ulcers Blog Post

By Lindsay Korac for STRUCTURE Supplements

Understanding Ulcers

If you are a horse owner, you have probably heard of ulcers. Equine Gastric Ulcer Syndrome (EGUS) is one of the most common gastrointestinal disorders affecting horses worldwide. Over the past 30 years, advances in veterinary medicine have transformed our understanding of gastric ulcer disease, revealing that ulcers are not limited to racehorses but occur across nearly every discipline, age group, and management system. Performance horses, breeding animals, pleasure horses, and even pasture-kept horses may develop gastric ulcers under certain conditions. Despite their prevalence, gastric ulcers often remain undiagnosed because the clinical signs are frequently subtle and can easily be attributed to behavioural issues, poor performance, or changes in temperament. As a result, understanding the causes, diagnosis, treatment, and prevention of gastric ulcers has become an essential component of modern equine management.

Understanding Ulcers

A gastric ulcer is a break or erosion in the lining of the stomach caused by exposure of underlying tissues to gastric acid and digestive enzymes. Unlike humans, horses produce stomach acid continuously (approximately 1.5 litres every hour) regardless of whether they are eating. This constant acid production is a consequence of the horse's evolutionary adaptation as a grazing species, designed to consume small amounts of forage throughout most of the day. The equine stomach is relatively small, holding only 8–15 litres, and is anatomically divided into two distinct regions:

The squamous (non-glandular) region, located in the upper third of the stomach, lacks protective mechanisms against acid exposure.

The glandular region, located in the lower two-thirds, produces hydrochloric acid, digestive enzymes, mucus, bicarbonate, and has an extensive blood supply that normally protects it from acid injury.

This distinction is clinically important because ulcers affecting these two regions develop through different mechanisms and often require different treatment approaches.
Today, gastric ulcer disease is generally divided into two categories: Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD). Although both conditions fall under the umbrella of Equine Gastric Ulcer Syndrome (EGUS), they differ considerably in their underlying causes, location within the stomach, disease mechanisms, and response to treatment. Numerous studies have demonstrated remarkably high prevalence rates across equine populations.

ESGD affects the squamous (non-glandular) region of the stomach, which lacks the protective mechanisms found in the lower glandular portion. As a result, this tissue is particularly susceptible to injury when acidic gastric contents splash onto the squamous mucosa during exercise, fasting, or periods of increased abdominal pressure. Consequently, ESGD is most commonly associated with management factors such as intermittent feeding, high-concentrate diets, intensive exercise, transportation, and other stressors that increase acid exposure. In contrast, EGGD develops within the glandular region of the stomach, where acid is continuously secreted but the mucosa is normally protected by a complex system of mucus, bicarbonate, adequate blood flow, prostaglandins, and tight epithelial junctions. Rather than excessive acid exposure alone, EGGD is believed to result from disruption of these protective mechanisms, leading to impaired mucosal defense and delayed healing. Consequently, the development of glandular disease is thought to involve a more complex interaction between stress, inflammation, immune function, and alterations in the gastric mucosal barrier.

Understanding the distinction between ESGD and EGGD has fundamentally changed how veterinarians approach the diagnosis and management of gastric ulcers. Historically, gastric ulcers were often considered a single disease process, with treatment focused primarily on reducing gastric acid production. However, growing evidence has shown that ESGD and EGGD are different diseases, meaning that successful management often requires different therapeutic approaches. While acid suppression remains highly effective for many cases of ESGD, horses with EGGD frequently require longer treatment durations and may benefit from additional therapies aimed at supporting mucosal protection and healing. This evolving understanding has also increased interest in nutritional strategies that support the integrity of the gastric lining and promote a healthy gastrointestinal environment, particularly for horses at ongoing risk of ulcer development.

Prevalence of Ulcers

Reported prevalence estimates include:
Thoroughbred racehorses: 80–100%
Standardbred racehorses: approximately 70–90%
Endurance horses: 50–70%
Show horses and sport horses: 30–60%
Pleasure horses: 10–50%

Figure 1: Reported prevalence of EGUS in different disciplines of horses

The modern management of horses differs substantially from the lifestyle for which their digestive systems evolved. Wild horses spend approximately 16–18 hours each day grazing, providing a continual flow of saliva and fibrous material into the stomach. Saliva contains bicarbonate, which helps buffer gastric acid, while forage creates a fibrous mat that limits acid splashing onto the sensitive squamous mucosa. In contrast, many domesticated horses experience prolonged fasting periods, consume large grain meals, undergo transportation, participate in strenuous exercise, and are exposed to various environmental stressors. Each of these management practices can disrupt normal gastric physiology and increase ulcer risk.

Exercise is particularly important because increased abdominal pressure compresses the stomach, forcing acidic gastric contents upward into the squamous region. During high-speed exercise, the pH within the upper stomach can fall dramatically, exposing unprotected tissues to highly acidic conditions. Consequently, gastric ulcers are especially prevalent in horses involved in racing, endurance, eventing, show jumping, and other athletic disciplines.

Risk Factors

Ulcer development is multifactorial, with several management, nutritional, and physiological factors contributing simultaneously.

Feeding Management

Perhaps the single greatest nutritional risk factor is intermittent feeding. Periods longer than four to six hours without forage allow gastric acid to accumulate within an empty stomach, reducing buffering capacity and increasing acid exposure to the squamous mucosa.

Additional dietary risk factors include:

• High-concentrate diets
• Large grain meals
• Low forage intake
• Limited pasture access
• Rapid dietary changes

Conversely, diets rich in forage stimulate saliva production, provide physical buffering within the stomach, and help stabilize gastric pH.

Exercise

Exercise increases gastric compression and acid splash, making exercise intensity one of the strongest predictors of squamous ulcer development. Even moderate exercise performed on an empty stomach has been shown to increase acid exposure of the squamous region.

Stress

Psychological and physiological stress may contribute through several mechanisms, including altered gastrointestinal motility, changes in blood flow, and increased cortisol concentrations.

Common stressors include:

• Transportation
• Hospitalization
• Competition
• Weaning
• Stall confinement
• Social isolation
• Illness or injury

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

Common medications such as phenylbutazone and flunixin meglumine inhibit prostaglandin synthesis. While effective for pain control, excessive or prolonged NSAID administration can reduce protective mucus production and impair blood flow within the glandular stomach, increasing susceptibility to glandular ulcers.

Diagnosis of EGUS and Grading

The definitive diagnosis of gastric ulcers requires gastroscopy, a procedure in which a three-metre video endoscope is passed through the horse's nostril into the stomach following a fasting period.

Gastroscopy allows veterinarians to

• Visualize ulcer location
• Determine ulcer severity
• Differentiate ESGD from EGGD
• Monitor healing following treatment

Ulcers are typically graded according to standardized scoring systems based on their number, depth, and appearance.

Although blood tests, behavioural assessments, and response to treatment may raise suspicion, none can reliably diagnose gastric ulcers without endoscopic examination.

Following gastroscopic examination, squamous gastric ulcers are typically graded using a standardized scoring system that describes the severity of mucosal damage. Ulcer grading allows veterinarians to objectively assess lesion severity, monitor healing over time, and evaluate responses to treatment. Although the appearance of ulcers does not always correlate with the severity of clinical signs, higher ulcer grades generally indicate more extensive damage to the squamous mucosa.

It is important to note that this grading system was developed specifically for ESGD. In contrast, EGGD is currently described based on lesion appearance, distribution, and characteristics (such as raised, depressed, fibrinosuppurative, or haemorrhagic lesions) rather than a universally accepted numerical grading system. This reflects the more complex nature of glandular disease and the ongoing research aimed at improving its classification.

Case Studies: Real-World Improvements in Equine Gastric

Ulcers Following STRUCTURE GI+ Supplementation

STRUCTURE GI+ was developed to support gastrointestinal barrier function, promote healthy inflammatory resolution, and provide nutritional support for the repair of the gastrointestinal lining through a blend of omega-3 and omega-6 fatty acids, antioxidants, and essential nutrients. While controlled scientific studies provide valuable evidence for evaluating nutritional supplements, individual clinical cases can also offer meaningful insight into how horses respond under real-world conditions. The following two horses underwent gastroscopy before and after a period of supplementation with STRUCTURE GI+ under veterinary supervision. Both horses initially presented with severe gastric ulceration and demonstrated marked improvement on repeat examination. These cases illustrate the potential role that targeted nutritional support may play as part of a comprehensive gastric health management program.

Case 1: Cheeto

Initial Gastroscopy (June 16th, 2025)

Cheeto presented with extensive squamous gastric ulceration. Endoscopic examination by Dr. Laura Frost from Halton Equine Veterinary Services revealed a Grade 4 equine squamous gastric disease (ESGD) characterized by:

• A large bleeding ulcer located along the lesser curvature of the stomach.
• Diffuse ulceration extending along the margo plicatus.
• Ulceration progressing toward the cardia (the opening of the esophagus into the stomach).
• Mildly raised ulcerative changes radiating from the pylorus toward the lesser curvature.
• The duodenum appeared normal.

This represented severe gastric disease with active tissue damage affecting a large portion of the squamous mucosa.

Follow-Up Gastroscopy (August 1st, 2025)

Following the supplementation period, repeat gastroscopy demonstrated remarkable healing. Veterinary examination found:

• Squamous ulcer score: Grade 1
• No evidence of active ulceration.
• Only a few small "island cells" along the margo plicatus, a normal anatomical variation that can occasionally resemble ulcers.
• No ulceration present within the glandular stomach.

Clinical Outcome

Over approximately six weeks, Cheeto improved from severe Grade 4 squamous ulceration with active bleeding to essentially complete resolution of visible ulcers. The follow-up examination demonstrated healthy gastric mucosa with no clinically significant ulcerative lesions remaining.

Case 2: Thunderstruck

Initial Gastroscopy (June 16th, 2025)

Thunderstruck presented with both severe squamous and glandular gastric disease. Gastroscopy identified:

• Multiple chronic, deep ulcerations extending throughout the entire margo plicatus and reaching the cardia.
• Diffuse sloughing of the squamous mucosa consistent with Grade 4 ESGD.
• Multiple linear erosions throughout the glandular stomach accompanied by surrounding inflammation (hyperemia).
• A moderate-to-large fibrinosuppurative lesion located within the pyloric antrum.
• A normal duodenum.

These findings indicated widespread damage affecting both the squamous and glandular regions of the stomach.

Follow-Up Gastroscopy (August 1st, 2025)

Repeat endoscopy demonstrated substantial healing after supplementation with STRUCTURE GI+. Findings included:

• Only several pinpoint ulcerations remaining at the margo plicatus (Grade 2 ESGD).
• The fibrinosuppurative lesion within the pyloric antrum remained present but was clearly progressing through the healing process.
• No progression of glandular disease was noted.

Clinical Outcome

Thunderstruck demonstrated a substantial reduction in ulcer severity over the supplementation period. The extensive Grade 4 squamous ulceration observed initially improved to mild Grade 2 lesions, while the previously noted pyloric lesion showed clear evidence of healing. Although complete resolution had not yet occurred, the follow-up examination indicated significant mucosal recovery.

What These Cases Demonstrate

These two clinical cases demonstrate meaningful improvements in gastric health following supplementation with STRUCTURE GI+, with both horses showing substantial reductions in ulcer severity confirmed by repeat veterinary gastroscopy.

Summary of Improvements

These cases highlight the potential for nutritional supplementation to support gastric healing when incorporated into a comprehensive management program. As with any gastric ulcer treatment plan, supplementation should be used alongside appropriate veterinary diagnosis.