Gastric ulcers in horses often show up as a cluster of subtle changes in behavior, appetite, body condition, and performance rather than one dramatic symptom. The challenge is that some horses with confirmed ulcers show no obvious signs at all, while others display problems that look like they could be caused by dozens of other issues. Knowing which signs to watch for, and which combinations raise the strongest red flags, can help you decide whether it’s time to call your vet for a definitive diagnosis.
Why Ulcers Are So Common in Horses
Horses produce stomach acid continuously, not just when they eat. In the wild, near-constant grazing keeps a buffer of food in the stomach. Domesticated horses that eat meals on a schedule can go hours with an empty stomach, leaving the upper lining exposed to acid with nothing to absorb it. Studies in Thoroughbred racehorses and show horses in active training have found gastric ulceration rates of 80 to 90 percent and around 60 percent, respectively. Even horses in lighter work develop them.
Exercise makes things worse through a specific mechanism: intense physical activity increases pressure inside the abdomen, compressing the stomach and pushing acidic contents upward onto the more vulnerable upper (squamous) lining. At the same time, stomach acid production actually increases during exercise. The combination of fasting between meals and regular hard work creates ideal conditions for ulcers to form, which is why performance horses are hit hardest.
The Most Common Signs to Watch For
No single symptom confirms ulcers on its own, but the more of these you see in the same horse, the stronger the case becomes.
- Reduced appetite or picky eating. A horse that leaves grain, eats slowly, or walks away from the feed bucket mid-meal may be experiencing stomach pain triggered by eating. Some horses prefer hay over concentrates, possibly because the chewing produces more saliva, which buffers acid.
- Weight loss or poor body condition. When eating hurts, horses eat less. Gradual weight loss that doesn’t respond to increased feed is one of the more reliable indicators.
- Poor coat condition. A dull, rough coat that doesn’t improve with grooming or nutrition changes can reflect chronic low-grade discomfort and the stress response it triggers.
- Recurring mild colic. Repeated episodes of low-grade belly pain, especially around feeding time or shortly after eating, are strongly associated with gastric ulcers. These episodes tend to be mild but frustratingly frequent.
- Diarrhea or loose manure. Not every horse with ulcers develops this, but intermittent soft stool without an obvious dietary cause is worth noting.
- Teeth grinding (bruxism). Horses that grind their teeth, particularly while eating or standing in the stall, may be responding to stomach pain. You’ll hear a distinctive grating sound.
Behavioral Changes Under Saddle and in the Barn
Ulcers frequently show up first as attitude problems rather than physical symptoms. A horse that becomes girthy, pinning ears, biting, or flinching when the girth is tightened, is a classic example. Veterinarians and equine nutritionists have long suspected a gastrointestinal link to girth aversion, and the connection to gastric ulcers is now well established. The girth sits right over the stomach area, and tightening it on an irritated stomach lining produces a pain response.
Beyond girthiness, watch for a horse that becomes sour about work it previously enjoyed: reluctance to go forward, resistance to collection, shortened stride, or refusing jumps. These performance declines are easy to blame on training issues or soreness elsewhere, which is why ulcers often go undiagnosed for months. Horses with gastric disease also show heightened stress responses to new environments or stimuli. Research has documented elevated cortisol (the primary stress hormone) in horses with ulcers when exposed to novel situations, suggesting these horses are in a chronic state of physiological stress that amplifies their reactions.
Stereotypical behaviors like cribbing, weaving, or stall walking may also have a connection to gastric pain. Researchers have proposed that ongoing stomach discomfort can trigger these repetitive behaviors, and that the behaviors sometimes persist even after the ulcers themselves are treated.
Signs That Are Easy to Miss
Some ulcer symptoms are so subtle they blend into the background. A horse that lies down more than usual in the stall, or that stands with a slightly tucked-up appearance in the flank area, may be managing discomfort you’d only notice if you were looking for it. The flehmen response, where the horse curls its upper lip, can sometimes indicate nausea or abdominal discomfort rather than the usual response to an interesting smell.
One of the trickiest aspects of equine ulcers is that horses with significant gastric disease can show no outward signs at all. Multiple studies have confirmed that some horses scoped with severe ulcers appear perfectly normal to their owners. This is especially true of ulcers in the glandular (lower) portion of the stomach, where research has found no reliable association between owner-reported symptoms and confirmed disease. So the absence of symptoms does not rule ulcers out, particularly in a horse with known risk factors like intense training, frequent travel, or long gaps between meals.
How Ulcers Are Diagnosed
Gastroscopy, where a veterinarian passes a long camera through the nose and down the esophagus into the stomach, is the only reliable way to confirm gastric ulcers in a living horse. It’s considered the gold standard, and no blood test, fecal test, or symptom checklist can replace it. The procedure requires the horse to fast (typically overnight) so the stomach is empty enough for the camera to see the lining clearly. It’s usually done standing, with sedation, and takes around 15 to 20 minutes.
During the scope, the vet looks at both the squamous (upper) and glandular (lower) portions of the stomach and grades any ulceration on a 0 to 4 scale. Grade 0 means intact, healthy tissue. Grade 1 shows thickening of the lining but no actual ulceration. Grade 2 involves small, localized lesions. Grade 3 means large or widespread superficial damage. Grade 4, the most severe, involves extensive ulceration with deep tissue damage. Knowing the grade helps determine how aggressive the treatment plan needs to be and how long it will take.
When Symptoms Point Toward Ulcers
If your horse shows two or three of the signs described above, particularly the combination of appetite changes, girthiness, and declining performance, ulcers should be high on the list of possibilities. Horses in regular training, those that travel frequently for shows, and those fed large grain meals with long hay-free gaps between feedings carry the highest risk.
The frustrating reality is that many of these symptoms overlap with other conditions: hindgut issues, dental problems, saddle fit, musculoskeletal pain, or simply a horse having an off week. That overlap is exactly why gastroscopy matters. Treating suspected ulcers without confirmation can mean spending weeks medicating a horse whose real problem lies elsewhere, while the actual issue goes unaddressed. A scope gives you a clear answer and a baseline to measure treatment success against when the horse is rescoped weeks later.