Gastric Ulcers in Horses: Signs, Causes, Treatment, and Prevention

By Dr Duncan Houston

A science-backed guide to recognising equine gastric ulcers, understanding the risk, and knowing what to do next.

Gastric ulcers are one of the most common hidden health problems in horses. They can affect racehorses, performance horses, pleasure horses, foals, and even well-managed horses that seem calm and healthy.

The frustrating part is that the signs are often vague. A horse may become girthy, picky with feed, dull, reactive under saddle, slow to perform, or mildly colicky. None of those signs prove ulcers are present, but they are enough to make gastric ulcers part of the conversation.

The key is not just asking, “Could this be ulcers?” The better question is: “What type of ulcer disease could this be, how serious is it, and what should be done next?”

Quick Answer

Equine gastric ulcer syndrome, or EGUS, is an umbrella term for ulceration and erosive disease affecting the horse’s stomach. Modern veterinary medicine separates this into equine squamous gastric disease, affecting the upper unprotected region of the stomach, and equine glandular gastric disease, affecting the lower acid-producing region. These two forms can look similar from the outside, but they can have different causes, risk factors, treatment responses, and recurrence patterns. (ScienceDirect)

Gastroscopy is the only way to definitively diagnose the presence, type, and severity of gastric ulcers in horses. Treatment usually centres on acid suppression with omeprazole, but management changes such as more forage, less fasting, lower grain intake, reduced stress, and careful NSAID use are just as important for preventing recurrence. (MSD Veterinary Manual)

What Are Gastric Ulcers in Horses?

Gastric ulcers are areas where the lining of the stomach becomes damaged, eroded, inflamed, or ulcerated. In horses, this is grouped under the term equine gastric ulcer syndrome, but that term is broad.

The more useful clinical breakdown is:

1. Equine Squamous Gastric Disease, or ESGD

2. Equine Glandular Gastric Disease, or EGGD

This distinction matters because the squamous and glandular regions of the stomach are not the same. The squamous region is the upper, non-glandular region. It has less natural protection from acid. The glandular region is the lower region that produces acid and has protective mechanisms such as mucus, bicarbonate, and blood flow. (Edu Veterinar)

In real-world terms, squamous ulcers are often linked to acid exposure, fasting, high grain diets, intense exercise, and acid splash. Glandular ulcers are more complicated and may involve breakdown of the stomach’s natural protective defences, stress, inflammation, NSAID exposure, and individual susceptibility. (MSD Veterinary Manual)

How Common Are Gastric Ulcers in Horses?

Gastric ulcers are very common, especially in horses under training, competition, travel, confinement, or other stressors.

MSD Veterinary Manual reports that equine gastric ulcer syndrome is estimated in at least 90 percent of racehorses in active training and racing, while non-racing performance horses vary from about 40 to 60 percent. (MSD Veterinary Manual)

The ECEIM consensus statement also reports very high rates in racehorses, with equine squamous gastric disease increasing from 37 percent in untrained Thoroughbreds to 80 to 100 percent within 2 to 3 months of race training. It also reports high prevalence in Standardbred racehorses, show and sport horses, and pleasure horses, though prevalence varies by breed, use, training intensity, and ulcer type. (Edu Veterinar)

The important point is this: ulcers are not only a racehorse disease. They are common in high-performance horses, but they can also occur in leisure horses, horses that travel, horses with social stress, horses with diet changes, horses receiving NSAIDs, and foals.

Why Do Horses Get Gastric Ulcers?

Horses are designed to graze for long periods. Their stomach produces acid continuously, even when they are not eating. UC Davis notes that horses produce stomach acid 24 hours a day, and that forage and saliva help buffer that acid during natural grazing. (Center for Equine Health)

Problems start when modern management works against that system.

Common triggers include:

1. Long gaps without forage

2. High grain or high concentrate diets

3. Low roughage intake

4. Stall confinement

5. Intense exercise

6. Transport

7. Competition stress

8. Social isolation or herd changes

9. Illness or pain

10. Chronic or repeated NSAID use

11. Abrupt feed changes

12. Returning to intense work immediately after treatment

In practice, I rarely think of gastric ulcers as a single-cause problem. They are usually a collision between acid exposure, stress, diet, workload, management, and individual vulnerability.

Why Are Squamous and Glandular Ulcers Different?

This is where many owner articles become too simplistic.

Squamous ulcers

Squamous ulcers affect the upper, non-glandular part of the stomach. This region is more vulnerable because it does not have the same level of natural acid protection as the glandular stomach.

Squamous ulcers are commonly associated with acid exposure. When a horse exercises, pressure changes can push acidic fluid upward, exposing the squamous mucosa to acid. This is often described as acid splash. Feeding before exercise, especially a small forage meal, may help create a fibre mat and buffering effect. (MSD Veterinary Manual)

Glandular ulcers

Glandular ulcers affect the lower, acid-producing region of the stomach. This region is normally protected, so glandular disease is less about simple acid splash and more about failure of the stomach’s protective mechanisms.

The causes are less clearly defined, but proposed factors include reduced blood flow, mucus-bicarbonate layer disruption, prostaglandin inhibition, inflammation, stress, and NSAID use. MSD notes that bacterial causes have not been proven in horses in the same way as some human ulcer disease. (MSD Veterinary Manual)

This matters because glandular ulcers can be harder to treat and may require longer therapy, additional medications, or repeat gastroscopy.

Signs of Gastric Ulcers in Horses

The signs of gastric ulcers are often vague. Some horses with significant ulcers show very little. Others show behavioural or performance changes before obvious appetite or weight changes.

Possible signs include:

1. Poor appetite

2. Picky eating

3. Slow eating

4. Walking away from feed

5. Weight loss

6. Poor body condition

7. Dull coat

8. Mild recurrent colic

9. Girthiness

10. Sensitivity around the flanks or belly

11. Irritability when groomed or tacked up

12. Reluctance to go forward

13. Reduced performance

14. Behaviour changes under saddle

15. Teeth grinding, especially in foals

16. Excess salivation or drooling in some foals

17. Diarrhoea in foals

Adult horses commonly show nonspecific signs such as poor performance, poor appetite, mild weight loss, attitude changes, and abdominal discomfort. MSD Veterinary Manual also notes that a strong correlation between ulcer severity and clinical signs has not been consistently reported. (MSD Veterinary Manual)

That means the horse with dramatic behaviour changes does not always have the worst ulcers, and the horse with severe ulcers may not always look severely unwell.

How Worried Should You Be?

Low Risk

Your horse is bright, eating well, maintaining weight, performing normally, passing normal manure, and has no colic signs.

This does not rule ulcers out, especially in performance horses, but it makes an immediate emergency less likely. Monitor patterns and risk factors.

Moderate Risk

Your horse has mild appetite changes, intermittent girthiness, subtle behaviour changes, poor coat, mild weight loss, or reduced performance.

This is a good time to involve your vet, especially if the signs are persistent, recurrent, or associated with training, travel, NSAID use, or feed changes.

High Risk

Your horse has recurrent colic signs, significant appetite reduction, rapid weight loss, marked behavioural change, repeated discomfort after eating, or is failing to improve despite ulcer treatment.

This needs veterinary assessment. The concern is not only ulcers. It may be ulcers plus another problem, or it may not be ulcers at all.

Critical Risk

Your horse has severe colic, persistent rolling, repeated attempts to lie down, sweating, collapse, fever, severe depression, inability to eat, signs of shock, or severe pain.

This is an emergency. Gastric ulcers may be present, but severe abdominal pain in adult horses is unlikely to be explained by uncomplicated gastric ulcers alone. MSD notes that horses with severe colic may have gastric ulcers, but the ulcers are unlikely to be the primary cause of severe abdominal pain. (MSD Veterinary Manual)

When Is This an Emergency?

Treat the situation as urgent if your horse shows:

1. Severe colic

2. Repeated rolling or violent pain

3. Collapse or profound weakness

4. Sweating with abdominal pain

5. Fast heart rate

6. Fever

7. Marked depression

8. Not eating at all

9. Persistent reflux signs

10. Repeated teeth grinding or severe discomfort in a foal

11. Foal lying on the back or showing significant abdominal pain

12. Signs of shock

Foals are a special concern. Gastric ulcer complications are more frequent and severe in foals, including delayed gastric emptying, reflux, oesophagitis, and rarely perforation. MSD Veterinary Manual notes that when foals show clinical signs, ulcers are typically severe and should be evaluated and treated immediately. (MSD Veterinary Manual)

What Else Can Look Like Gastric Ulcers?

This is one of the biggest clinical traps.

Many horses are labelled as “ulcery” because they are girthy, reactive, underperforming, or fussy with feed. Sometimes that is correct. Sometimes it is not.

Other problems that can look similar include:

1. Dental disease

2. Hindgut disease

3. Right dorsal colitis

4. Sand enteropathy

5. Inflammatory bowel disease

6. Liver disease

7. Pain from lameness

8. Back or sacroiliac pain

9. Poor saddle fit

10. Ovarian or reproductive pain in mares

11. Poor diet formulation

12. Parasite burden

13. Chronic low-grade colic

14. Delayed gastric emptying

15. Behavioural stress or learned responses

16. Overtraining or fatigue

17. Respiratory disease affecting performance

The mistake is assuming ulcers explain everything. In practice, the horse that does not improve with appropriate ulcer treatment needs the diagnosis reopened, not just another tub of supplement.

How Are Gastric Ulcers Diagnosed?

The gold standard is gastroscopy.

Gastroscopy involves passing a long endoscope into the stomach after appropriate fasting so the vet can directly examine the stomach lining. It allows the vet to see whether ulcers are present, where they are, how severe they are, and whether they affect the squamous or glandular region. (MSD Veterinary Manual)

This matters because treatment decisions can change depending on what is found.

A horse with classic squamous ulceration may respond well to standard omeprazole therapy and management change. A horse with glandular disease may need longer treatment, sucralfate, misoprostol in selected cases, or more careful investigation of stress, pain, NSAID exposure, and recurrence triggers. (MSD Veterinary Manual)

Empirical treatment may be used when gastroscopy is not available, but it has limits. If the horse does not respond as expected, gastroscopy becomes much more important.

What Does Science Say About Treatment?

The main evidence-backed treatment for equine gastric ulcers is acid suppression, especially omeprazole.

GastroGard is FDA approved for treatment and prevention of recurrence of gastric ulcers in horses and foals four weeks of age and older. The labelled treatment dose is once daily for four weeks at 4 mg/kg, with a lower daily maintenance dose used for prevention of recurrence. (DailyMed)

In 2026, the FDA also approved Gastrobim, the first generic omeprazole oral paste for treatment of gastric ulcers and prevention of recurrence in horses and foals four weeks of age and older. The FDA states that Gastrobim contains the same active ingredient as GastroGard and was determined to be bioequivalent to the brand-name product. (U.S. Food and Drug Administration)

For prevention, UlcerGard has FDA approval for prevention of gastric ulcers in horses. The FDA’s approval summary reports omeprazole at 1 mg/kg daily as effective for prevention of gastric ulcers in horses exposed to ulcerogenic conditions. (Animal Drugs at FDA)

The key point: use properly regulated, veterinarian-directed medication where available. Do not assume every ulcer paste, powder, supplement, or compounded product is equivalent.

Does Omeprazole Work for Every Horse?

No.

Omeprazole is very important, but it is not magic dust.

Squamous ulcers tend to respond better to acid suppression than glandular ulcers. The Veterinary Journal review notes that treatment is usually successful in equine squamous gastric disease, but less so in equine glandular gastric disease, where treatment may need to be longer and additional therapies such as sucralfate or misoprostol may be considered. (ScienceDirect)

MSD Veterinary Manual also notes that glandular disease may require 45 to 60 days of treatment, and repeat gastroscopy may help guide treatment duration. (MSD Veterinary Manual)

This is why repeat assessment matters. If the horse looks better, great. If the horse only partially improves, relapses quickly, or never improves, the answer is not automatically “more omeprazole.” The answer is: confirm the diagnosis, identify the ulcer type, and reassess the whole horse.

What About Supplements?

Supplements may support management in some cases, but they should not replace diagnosis, medication, and management correction when true ulcers are present.

The supplement problem is simple: the market is full of confident claims, but not all products have strong clinical evidence. Some may help with buffering, mucosal support, or feeding routine. Others are mostly expensive optimism in a tub.

Supplements are not the first thing I would rely on for a horse with confirmed moderate to severe ulceration, ongoing colic, significant appetite changes, or weight loss.

The stronger plan is:

1. Diagnose properly where possible

2. Use evidence-backed medication when indicated

3. Correct the feeding pattern

4. Reduce fasting

5. Adjust workload and stress

6. Recheck response

7. Use supplements only as part of a wider plan, not instead of one

What Should You Do If You Suspect Gastric Ulcers?

Step 1: Look at the whole pattern

Write down what has changed:

1. Appetite

2. Weight

3. Coat condition

4. Manure

5. Behaviour under saddle

6. Girth reaction

7. Performance

8. Travel schedule

9. Training intensity

10. Turnout

11. Forage access

12. Grain intake

13. NSAID use

14. Recent illness or stress

Patterns matter more than isolated moments.

Step 2: Contact your vet

If the signs are persistent, recurrent, or affecting performance, appetite, or body condition, involve your vet. Gastroscopy is the clearest way to know whether ulcers are present and what type they are.

Step 3: Do not keep guessing with random products

Trying five supplements before diagnosis can waste time and money. Worse, it can delay investigation of other problems.

Step 4: Reduce obvious risk factors

While waiting for veterinary assessment, focus on safe management basics:

1. Avoid long fasting periods

2. Increase forage access

3. Reduce grain where appropriate

4. Avoid abrupt feed changes

5. Reduce intense work if the horse is uncomfortable

6. Avoid unnecessary NSAID use

7. Provide turnout where possible

8. Support social contact if safe

Step 5: Reassess after treatment

If your horse is treated for ulcers, response should be monitored. If signs recur rapidly after treatment stops, that usually means the underlying management or medical trigger has not been solved.

Management Changes That Help Prevent Ulcers

Medication can help heal ulcers, but management helps stop them coming back.

Research-backed prevention focuses on reducing acid exposure, supporting saliva and forage buffering, lowering high-risk feeding patterns, and reducing stress.

Practical prevention steps include:

1. Provide frequent forage or free-choice forage where safe

2. Avoid long periods without hay or pasture

3. Use slow feeders if appropriate

4. Reduce large grain meals

5. Split concentrate meals into smaller feeds

6. Consider adding some alfalfa, especially before exercise, if suitable for the horse

7. Feed a small forage meal before work

8. Reduce unnecessary intense training during treatment

9. Minimise repeated transport stress where possible

10. Avoid chronic NSAID use without veterinary monitoring

11. Give horses visual and social contact when stabled

12. Recheck horses that relapse

UC Davis recommends frequent feeding or free-choice pasture to buffer stomach acid and stimulate saliva production, reducing grain and concentrates, adding alfalfa where appropriate, limiting stressors such as intense training and frequent transporting, and allowing stabled horses access to forage and social contact. (Center for Equine Health)

Common Mistakes Owners Make

Mistake 1: Assuming girthiness always means ulcers

Girthiness can be ulcers, but it can also be pain, saddle fit, learned behaviour, muscle soreness, ovarian pain, back pain, or poor handling history.

Mistake 2: Treating without changing management

If a horse returns to the same long fasting periods, high grain meals, intense exercise, and stress, ulcers can come back.

Mistake 3: Using supplements instead of diagnosis

Supplements may have a place, but they are not a replacement for gastroscopy and evidence-backed treatment in a horse with significant signs.

Mistake 4: Forgetting about glandular disease

Glandular ulcers can be more stubborn. If a horse is treated but does not respond as expected, the ulcer type and diagnosis need reassessment.

Mistake 5: Ignoring NSAID risk

Bute, flunixin, and other NSAIDs can be appropriate, but repeated or chronic use needs veterinary oversight, especially in horses with appetite changes, dehydration, colic, or suspected gastrointestinal disease.

Mistake 6: Blaming ulcers for every performance issue

Ulcers are common, but they are not the answer to every poor performance case. Lameness, back pain, respiratory disease, dental disease, and training issues still need to be considered.

Myth vs Reality

Myth: Only racehorses get ulcers

Reality: Racehorses are high risk, but any horse can develop ulcers, including sport horses, leisure horses, foals, and well-managed horses exposed to stress or dietary risk factors.

Myth: If the horse is eating, ulcers are unlikely

Reality: Some ulcer horses keep eating. Others show subtle changes such as slower eating, picky eating, or walking away from feed.

Myth: If omeprazole does not work, it cannot be ulcers

Reality: Glandular ulcers can respond less predictably than squamous ulcers. The dose, formulation, timing, compliance, ulcer type, and underlying triggers all matter.

Myth: Supplements are safer, so they should be tried first

Reality: Safe does not always mean effective. A horse with significant ulcers, weight loss, recurrent colic, or ongoing discomfort needs veterinary assessment.

Myth: Once ulcers heal, the problem is finished

Reality: Ulcers commonly recur if the original risk factors remain.

Can Gastric Ulcers Go Away on Their Own?

Mild lesions may improve if risk factors are removed, but ongoing training, travel, fasting, confinement, high grain intake, illness, and NSAID exposure can prevent healing or drive recurrence.

MSD Veterinary Manual notes that spontaneous healing has been observed, but if training, racing, and risk factors continue, lesions are unlikely to heal without medical intervention. (MSD Veterinary Manual)

So yes, some mild cases may improve with better management, but confirmed or clinically significant ulcers should not be treated casually.

What Is the Prognosis?

The prognosis is usually good when ulcers are recognised, diagnosed properly, treated appropriately, and management changes are made.

UC Davis notes that gastric ulcers can often be treated and prevented, with many healing within around four weeks of treatment. (Center for Equine Health)

The prognosis becomes more guarded when:

1. The horse has glandular disease

2. Ulcers recur quickly

3. Risk factors cannot be changed

4. The horse has repeated colic

5. The horse is a foal with clinical signs

6. There may be delayed gastric emptying or another underlying disease

7. The horse is treated repeatedly without gastroscopy

The real goal is not just healing the ulcer. The real goal is stopping the cycle that caused it.

FAQs

What is the best test for gastric ulcers in horses?

Gastroscopy is the best test. It allows direct visualisation of the stomach lining and helps determine whether ulcers are present, where they are, and whether they affect the squamous or glandular region. (MSD Veterinary Manual)

Can gastric ulcers cause colic in horses?

Yes, ulcers can be associated with mild or recurrent colic signs. However, severe colic in an adult horse should not be assumed to be simple gastric ulcers. Severe pain needs urgent veterinary assessment.

Is omeprazole the best treatment for horse ulcers?

Omeprazole is the main evidence-backed treatment for equine gastric ulcers, especially squamous disease. Glandular disease may need longer treatment and additional medication such as sucralfate or misoprostol in selected cases under veterinary guidance. (MSD Veterinary Manual)

Can horse ulcers come back after treatment?

Yes. Ulcers can recur if the original risk factors remain, such as long fasting periods, high grain diets, intense training, stress, travel, or ongoing NSAID exposure. UC Davis notes that ulcers can return after treatment ends if management changes are not made. (Horse Report)

Should I feed hay before exercise?

A small forage meal before exercise may help protect the squamous region by creating a fibre barrier and buffering acid splash. Alfalfa can be useful for some horses because of its calcium and protein buffering properties, but dietary changes should be tailored to the individual horse. (Horse Report)

Final Thoughts

Gastric ulcers in horses are common, but they should not be treated like a simple one-size-fits-all problem.

The most important shift is understanding that “ulcers” is not a complete diagnosis. Squamous and glandular disease are different. Signs can be vague. Some horses show very little. Others look dramatic. Supplements are not all equal. Medication works best when the management problem is corrected at the same time.

If your horse is girthy, picky with feed, losing condition, underperforming, mildly colicky, or behaving differently under saddle, ulcers may be part of the picture. But the best plan is not guessing. The best plan is proper veterinary assessment, evidence-backed treatment when needed, and a management routine that supports the way a horse’s stomach is actually built to function.

If you are unsure whether your horse’s signs could be ulcers, pain, diet-related, or something more urgent, ASK A VET™ can help you make the next decision with clearer guidance.