Introduction: Why Recognising Ulcers Early Matters
Gastric ulcers are painful erosions in a horse’s stomach or upper small intestine, and they affect far more horses than most owners realise. Studies estimate that 60–90% of racehorses and 40–60% of performance horses have some degree of gastric ulceration at any given time.
This article focuses specifically on the early and advanced signs of ulcers in horses, helping you recognise when something is wrong and when to call your veterinarian.
The tricky part is that subtle behavioural changes are often the earliest warning signs, appearing long before dramatic symptoms such as significant weight loss or obvious colic. A horse that becomes irritable when being girthed, seems reluctant to move forward under saddle, or starts leaving grain in the bucket may be experiencing ongoing abdominal discomfort from gastric ulcers. These vague clues are easy to dismiss as training issues or quirks of temperament.
Equine gastric ulcer syndrome is the umbrella term veterinarians use to describe ulceration affecting both the non-glandular (squamous) and glandular portions of the equine stomach. Clinical signs can differ between foals and adult horses, and between squamous ulcers in the upper stomach and glandular ulcers near the pylorus.
Consider a 10-year-old Thoroughbred in regular work whose only initial sign was a sour attitude when being tacked up—ears pinned, moving away from the girth, and snapping at the handler. On gastroscopy, this horse had Grade 3 squamous lesions that responded well to treatment. That’s the reality of equine ulcers: the signs can be maddeningly subtle, but catching them early makes all the difference.
Horse that was recently saddled with its ears pinned back.
Quick Reference: Common Signs of Ulcers in Horses
If you’re short on time, here’s a fast overview of the most frequently reported signs in adult horses. Use this as a checklist to compare against your horse’s recent behaviour:
Reduced appetite or slow eating
Leaving grain but continuing to pick at the hay
Gradual weight loss over several weeks
Dull, lacklustre coat
Attitude changes under saddle (sourness, resistance)
Reluctance to move forward or extend stride
Girthiness—biting, kicking, or moving away when girthed
Grinding teeth (bruxism)
Recurring mild colic, especially 1–2 hours after meals
Stretching out as if to urinate without actually urinating
Additional management-related signs to watch for:
Fidgeting or refusing to stand still when being girthed
Tail swishing under saddle without an obvious cause
Pinning ears when groomed around the flank or girth area
Lying down more frequently after hard work or competitions
Pawing or looking at the flank intermittently
Keep in mind that some horses show no obvious outward signs even with moderate to severe ulceration.
If your horse’s performance or behaviour has shifted without explanation, a veterinary evaluation is warranted.
Understanding Gastric Ulcers in Horses
Gastric ulcers in horses are erosions or sores that develop in the stomach lining and sometimes extend into the proximal duodenum of the small intestine. Unlike humans, who typically develop ulcers from bacterial infection, horses develop ulcers primarily from prolonged exposure of vulnerable tissue to stomach acid and volatile fatty acids.
The horse’s stomach is designed for near-constant grazing, but modern management often involves high-grain diets, infrequent meals, and prolonged periods without forage—all of which set the stage for ulcer formation.
Veterinarians now distinguish between two main types: equine squamous gastric disease, which affects the upper, non-glandular portion of the stomach, and equine glandular gastric disease, which occurs in the lower, acid-producing glandular region. Most lesions—roughly 70–80%—are found in the squamous mucosa near the margo plicatus, the visible ridge where the two tissue types meet. Glandular ulcers tend to occur closer to the pylorus, where the stomach connects to the small intestine.
The reason horses are particularly vulnerable comes down to physiology. Unlike dogs or humans, horses continuously secrete gastric acid whether they are eating or not. When a horse’s stomach is empty—during long gaps between meals or overnight fasting—that acidic fluid has nothing to buffer it. During intense exercise, abdominal pressure increases, splashing acid up onto the unprotected squamous portion.
This explains why stabled horses, horses prone to stress, and performance horses in heavy training have such high ulcer prevalence.
Behavioural and Performance Signs of Ulcers in Adult Horses
Many horse owners first suspect ulcers not because of weight loss or colic, but because their horse’s attitude and performance have changed. These behavioural shifts can be frustrating to pin down, especially when the horse otherwise appears healthy.
Here are the key behavioural and performance-related clinical signs to watch for:
Irritability and attitude changes:
Pinning ears during grooming, especially around the girth and flank
Aggression toward other horses at feeding time
Increased sensitivity to leg aids
Snapping or threatening when approached with tack
General “sourness” that wasn’t present before
Performance-related clues:
Reluctance to go forward or extend stride
Resistance to collection or lateral work
Reluctance to bend in one or both directions
Frequent breaking gait without an obvious cause
Refusing jumps when there is no apparent lameness
Shortened stride or “choppy” movement
Girth-related signs:
Biting at the girth or the handler’s hands during tacking
Moving away, circling, or kicking at the belly when the girth is tightened
Fidgeting or cow-kicking when the saddle is placed
Visible flinching or tensing when pressure is applied to the girth area
Training inconsistency:
Good days and bad days with no clear pattern
Performance worsening after competitions, travel, or changes in routine
Improvement on days with more turnout or forage access
Consider a 7-year-old eventer who began stopping at fences seemingly out of nowhere. He’d swish his tail aggressively when asked to canter and would grind his teeth during flatwork. His rider assumed it was a training issue until gastroscopy revealed extensive squamous ulcers along the margo plicatus. Within three weeks of treatment and management changes, the refusals stopped entirely.
One particularly telling statistic: in a study of horses described as “girthy” by their owners, 92% were found to have gastric ulcers on endoscopic examination. That persistent girth sensitivity isn’t just a behavioural quirk—it’s often a sign of genuine abdominal discomfort.
Horse looking uncomfortable when riding in an outdoor arena.
Physical and Digestive Signs of Ulcers in Adult Horses
Beyond behaviour, ulcers often manifest as vague physical changes that develop gradually over weeks or months. These signs rarely scream “emergency,” but they paint a picture of a horse that isn’t thriving.
Appetite changes:
Slow eating, taking longer than usual to finish meals
Leaving some concentrate in the bucket when this is a new behaviour
Walking away from the feed tub mid-meal
Preferring hay to grain (decreased appetite for concentrates specifically)
Eating eagerly at first, then backing off as if eating causes discomfort
Weight and condition changes:
Gradual weight loss despite adequate feed
Loss of topline and muscle definition
A “tucked up” or gaunt appearance through the flank
Poor body condition that doesn’t respond to increased calories
Dull coat that lacks normal shine
Gastrointestinal discomfort:
Mild, recurrent colic, especially 1–2 hours after meals
Stretching out as if to urinate without producing urine
Looking at or biting at the flank
Pawing intermittently, particularly after eating
Lying down more than usual, especially after hard work
Frequent yawning (sometimes associated with nausea or discomfort)
Other subtle signs:
Grinding teeth or "Bruxism" (more common in foals but seen in adults)
Excessive salivation in some cases
Softer droppings or occasional loose stools
Changes in eating habits that seem inconsistent or unpredictable
It’s worth emphasising that these signs overlap significantly with other conditions.
Dental problems, parasites, hindgut issues, and musculoskeletal pain can all produce similar presentations. The presence of several signs together—particularly in a horse with risk factors such as high-stress management, frequent travel, or intense exercise—should prompt a conversation with your veterinarian rather than just making assumptions about the cause. (Better to get the horse checked out and be safe than sorry.)
Signs of Ulcers in Foals
Foals from birth to around six months of age can develop severe ulcers remarkably quickly, often in association with illness, hospitalisation, maternal separation, or other stressors.
Unlike adult horses, where signs may simmer for weeks, foals can deteriorate rapidly, and the stakes are higher—perforation of the stomach, though rare, can be fatal.
Key signs of ulcers in foals:
Intermittent or continuous colic (pawing, rolling, looking at the flank)
Lying on their backs or in unusual positions (dorsal recumbency)
Teeth grinding (bruxism)—this is particularly characteristic in foals
Excessive drooling or frothing from the mouth or nostrils
Restlessness, repeatedly getting up and lying down
Nursing and growth clues:
Poor or interrupted nursing
Repeatedly approaching the mare, then pulling away
Slow weight gain compared to age-matched foals
A pot-bellied appearance despite adequate milk intake
Failure to thrive despite an apparently healthy dam
Diarrhea:
Watery, foul-smelling stools
Loose droppings that persist beyond normal foal heat diarrhoea
Diarrhoea combined with any colic-like behaviour
Any colic-like behaviour or refusal to nurse in a foal should be treated immediately as an emergency.
Foals do not have the reserves that adult horses do, and delays in treatment can lead to severe gastric ulceration, dehydration, and life-threatening complications. If you see a foal lying on its back repeatedly, grinding its teeth, or nursing poorly, contact your veterinarian the same day.
When to Suspect Squamous vs. Glandular Ulcers Based on Signs
Only gastroscopy can provide a definitive diagnosis of ulcer type and location, but certain patterns in your horse’s signs can help guide the conversation with your vet.
Patterns suggestive of squamous ulcers:
Pain or behaviour changes clearly tied to meals or working on an empty stomach
Signs that flare after high-intensity exercise or competition
Improvement when given hay or alfalfa hay before riding
Classic “hungry horse” presentation—eager to eat, then uncomfortable
Patterns suggestive of glandular ulcers:
More continuous poor appetite without clear meal-related triggers
Chronic low-grade colic that isn’t obviously tied to eating or exercise timing
Marked girthiness even at low work levels
A persistently “sour” attitude that doesn’t improve with management tweaks
Signs that seem more random or unpredictable
Some horses have both squamous and glandular ulceration at the same time, which can muddy the picture. Glandular ulceration may also be associated with changes in blood flow to the gastric mucosa and may respond differently to treatment than squamous disease.
These patterns are not diagnostic—they’re conversation starters. Use them to help your veterinarian understand what you’re seeing, but don’t attempt to self-classify the ulcer type or adjust treatment protocols without professional guidance.
How Veterinarians Confirm Ulcers and Grade Their Severity
Many of the signs discussed above are nonspecific—they could point to ulcers, but they could also indicate dental disease, hindgut pathology, pain elsewhere in the body, or behavioural issues. Gastroscopy (endoscopic examination of the stomach) remains the only reliable method for a definitive diagnosis.
The gastroscopy procedure:
Fasting: Your horse will typically be fasted for 12–16 hours before the procedure (hay removed overnight) and water withheld for 2–4 hours. This allows the stomach to empty so the vet can visualise the entire gastric mucosa.
Sedation: Light sedation keeps the horse calm and comfortable while the endoscope is passed.
Scope insertion: A 10-foot (about 3-meter) long flexible endoscope is passed through the horse’s nostril, down the oesophagus, and into the stomach.
Visualisation: The veterinarian examines the squamous region, the margo plicatus, the glandular region, and the area near the pylorus. Photos or video are often taken for documentation.
Grading: Lesions are typically graded on a 0–4 scale:
Grade 0: Intact mucosa, no lesions
Grade 1: Reddening or hyperkeratosis, mucosa intact
Grade 2: Small, single, or multiple ulcers
Grade 3: Large single or multiple ulcers
Grade 4: Extensive lesions with deep or severe ulceration
This ulceration severity grading helps guide gastric ulcer treatment decisions, including medication type, dosage, and duration. It’s also useful for recheck endoscopy to monitor ulcer healing.
In situations where scoping isn’t immediately available, veterinarians may make a presumptive diagnosis based on clinical signs, risk factors, and response to a trial of ulcer medication such as omeprazole paste. This proton pump inhibitor works by suppressing gastric acid secretion, increasing gastric pH, and promoting healing of the stomach lining.
The procedure itself is safe and typically completed within 20–30 minutes. Most horses go home the same day and can return to normal feeding within hours.
A mare and foal in a lush green pasture.
Next Steps if You See Signs of Ulcers in Your Horse
Persistent behaviour changes, unexplained weight loss, recurrent mild colic, or nursing changes in foals are all reasons to call your veterinarian promptly.
Don’t wait for signs to become severe—horses with gastric ulcers often have a poor correlation between lesion severity and outward symptoms. A horse with Grade 4 ulcers may show only subtle performance decline, while another with milder disease might display more obvious distress.
Immediate owner actions while waiting for veterinary evaluation:
Keep a daily log of appetite, manure consistency, and behaviour
Ensure continuous access to forage (hay or pasture) to buffer stomach acid
Avoid sudden feed changes or prolonged fasting
Reduce intense exercise until your horse has been evaluated
Note any stressful situations (travel, competition, herd changes) that preceded the signs
Important cautions:
Do not start or stop prescription medications without veterinary guidance
Avoid prolonged NSAID use, as these can worsen glandular disease
Don’t assume improvement means the problem is solved—affected horses may need recheck endoscopy to confirm ulcer healing
The good news is that many horses improve significantly within 2–4 weeks of appropriate treatment, nutritional management adjustments, and stress reduction. Preventing gastric ulcers from recurring requires addressing the underlying risk factors: feeding horses frequent meals or free-choice forage, reducing stall confinement, managing travel stress, and avoiding an empty stomach before work.
Early recognition of signs and symptoms gives your horse the best chance at a quick recovery and return to comfortable, willing work.
If you’ve noticed several of the signs described in this article—especially if you have a performance horse, a horse under stress, or a young foal—don’t wait. Schedule a veterinary exam as soon as possible to discuss the best approach to care for your horse, whether that is a gastroscopy or something else.