For decades, equine gastric ulcer syndrome (EGUS) has been blamed for everything from girthiness and ear pinning to bucking under saddle. While many horses do improve after ulcer treatment, new research presented at the 2026 International Society for Equitation Science conference suggests the relationship between ulcers and behaviour is more complicated than many people assume.
A recent review by Ben Sykes and Amy Lovett doesn’t dismiss the role of ulcers — in fact, it reinforces that EGUS can be an important cause of pain-related behaviour. However, the authors argue that veterinarians and horse owners should stop asking, “Does this horse have ulcers?” and instead ask, “What is causing this horse’s pain?”
Their conclusion: ulcers are one possible contributor, but rarely the whole story.
The first point the authors make is that undesirable behaviour should never automatically be dismissed as poor training or a bad attitude. Horses may become defensive, resistant or anxious because they anticipate pain. Behaviour such as refusing to move forward, threatening to bite while being saddled, bucking, tail swishing or avoiding/resisting the bit can all be expressions of discomfort rather than disobedience.
That doesn’t mean every behavioural problem is pain-related; fear, anxiety, hormones and inadequate training all influence behaviour. The key distinction is whether the horse develops new aversive responses to activities that should not normally be painful.
The review draws an important comparison with chronic pain in humans. Long-term pain changes emotional state, increasing anxiety, irritability and sensitivity. Horses likely experience similar changes, and one that appears “grumpy” or “spooky” may actually be living with chronic discomfort.
So where do ulcers fit? Clinical experience strongly suggests that many horses with EGUS improve behaviourally after treatment. Scientific evidence, however, is mixed.
Some studies report that approximately one-third of horses diagnosed with either equine squamous gastric disease (ESGD) or equine glandular gastric disease (EGGD) present with behavioural changes, while around one-quarter to one-third show girthiness. Other research has failed to find a clear relationship between ulcer severity and owner-reported behavioural signs. Even more confusing, some horses show complete healing of gastric lesions on gastroscopy, but continue to display the same undesirable behaviours.
While these findings appear contradictory, the authors suggest several reasons. First, many horses have multiple painful conditions at the same time. Musculoskeletal pain, poorly-fitting tack, dental disease and gastric ulcers frequently coexist. Treating only one problem may not eliminate the horse’s discomfort. Second, behaviour can become learned. If saddling has been painful for months because of ulcers, the horse may continue to anticipate pain and react defensively even after the ulcers heal.
This distinction is clinically important, because healing tissue does not necessarily erase established behavioural patterns.
The review also discusses the growing use of objective pain assessment tools, particularly the Ridden Horse Pain Ethogram (RHpE), which scores specific ridden behaviours associated with pain.
One recent study found strong correlations between RHpE scores and both squamous and glandular ulcers. As ulcer severity improved, pain-related ridden behaviours also declined. Although more research is needed, this provides some of the strongest evidence to date linking EGUS with ridden performance problems.
Perhaps the paper’s most valuable contribution is its proposed diagnostic approach. Instead of searching for a single explanation, the authors recommend evaluating horses through multiple “lenses.” In horses presenting with aversive behaviour during riding or saddling, musculoskeletal pain should generally be considered the leading differential diagnosis. Gastric ulcers rank alongside it, particularly when accompanied by recent colic, poor appetite, altered eating behaviour or unexplained weight loss. Dental disease, tack fit and other painful disorders also deserve investigation.
Rather than treating ulcers in isolation, clinicians should evaluate the whole horse.
The authors also emphasize the importance of therapeutic response. If ulcer treatment substantially improves behaviour, the ulcers were likely contributing to the problem. If improvement is only partial, additional painful conditions should be investigated rather than assuming treatment has failed.
Behaviour modification may also be necessary. When horses have developed anticipatory responses, such as becoming defensive before the girth is even tightened, the pain may have been addressed, but the expectation of pain remains. Careful retraining, positive associations during tacking and consistent, low-stress handling may be needed alongside medical treatment to break these learned patterns.
Perhaps the paper’s most important message is how success should be defined. Veterinarians often focus on healing visible disease. Owners care whether their horse becomes comfortable to ride again. The authors argue that both outcomes matter. A horse whose ulcers have healed, but still displays pain-related behaviour, has not achieved a truly successful clinical outcome.
Gastric ulcers should neither be blamed for every behavioural issue, nor dismissed because the evidence is sometimes inconsistent. Instead, they should be considered one component of a broader pain assessment. The challenge is identifying every source of discomfort, not just the most obvious one.
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