A number has been circulating in the horse world for years. Sixty percent of sport horses have a gastric ulcer. It is the kind of statistic that shows up on every other Instagram slide, usually next to a photo of a horse with sad eyes and an empty feed bowl. Alarming enough to make you pause. Not quite alarming enough to make most owners actually change anything.
The real problem is that the number has been too low for years.
What the Research Actually Shows
Dig into the veterinary literature and a different picture appears. The most authoritative source on the subject, the 2015 European College of Equine Internal Medicine consensus statement, places prevalence somewhere between 40% and 90%, depending on discipline and training load, climbing to 100% in racehorses in active training. A 2025 study of horses from a French cavalry regiment found ulcers in 88% of the animals examined. And an older, still widely cited source puts it simply: 60% of sport horses, in every discipline, including show jumping and dressage, carry gastric ulcers. That was already the average. Not the ceiling.
The most revealing number, though, doesn't come from France or a global meta-analysis. It comes from Lisbon. A master's thesis at the veterinary faculty of the Universidade de Lisboa used gastroscopy to examine twelve Lusitanos, Portugal's own national breed, for signs of gastric ulceration. Twelve out of twelve had lesions on the gastric mucosa. 100%.
Twelve horses is not a representative sample, and that's worth saying plainly. But it is the only direct evidence on this subject to come out of Portugal itself, in the national breed, under the stabling conditions those horses actually live in. And the thesis points to exactly the same culprits the international literature has flagged for years: management, diet, exercise and stress, with permanent box stabling named as one of the clearest risk factors.
Where It Comes From
To see why that matters so much, it helps to know how a horse's stomach actually works. It produces acid around the clock, whether there is anything in it or not. In the wild, a horse spends 14 to 16 hours a day grazing and chewing, which means there is almost always forage in the stomach to absorb that acid. Saliva is the only natural buffer against it, and saliva is only produced by chewing. Chewing hay produces roughly four times more saliva per kilo than chewing the same amount of concentrate feed.
Three things in stable management break that balance, over and over, in every study that measures them:
- Long gaps without forage. Veterinary research puts the danger line at more than six hours between forage meals, past which the risk of squamous ulcers climbs. It's part of why Prime Hay advises never leaving a horse longer than three hours without something to chew: the stomach doesn't wait for hour six to start producing acid.
- Starch-heavy diets. When hay is poor, the usual response is to add more concentrate. That's exactly backwards. Higher starch intake is linked to nearly double the risk of squamous ulceration.
- Stress and workload. Frequent training, transport and limited turnout all raise prevalence, consistently, across every study that looks.
Portugal and Spain: What We Know, and What We Don't
No large-scale study has measured how often this happens in Spanish or Portuguese sport and leisure horses, whether in dressage, show jumping or a weekend hack. That's a genuine gap in the research, and it's more honest to say so than to invent a number to fill it.
What does exist points the same way. The Lisbon thesis confirms that, even in a small sample of Lusitanos, permanent stabling and diet are risk factors identified in Portugal itself, not only in international literature. A Spanish study of horses competing at national and international level in show jumping, dressage and eventing describes the same classic EGUS signs, poor appetite, recurrent colic, teeth grinding, low energy, tied to competition stress and changes in stabling.
And anyone who spends time around equestrian centres in Spain and Portugal recognises a pattern that nobody would call bad management, but that happens to line up exactly with the risk factors the literature describes. Many horses spend most of the day in an individual box, with turnout limited to an hour or two, often because yards sit close to cities where space is expensive. In summer, when it's too hot for long turnout, rations quietly shift toward more concentrate and less forage. Nobody is doing anything wrong. The system is simply lining up the same way it does in every study where the numbers come out high.
What Actually Changes This
The good news, and it's the part that usually gets left out of the alarming social posts, is that the fix is not an expensive intervention. It doesn't require a different yard, a different discipline or an entirely new feeding programme. It comes down to four things, each of them small.
- Forage first, always. At least 1.5 to 2% of bodyweight in hay per day, spread out so there is never more than three hours with nothing to chew.
- Cut concentrate before you cut hay. If the feed bucket is compensating for weak hay, more feed won't fix it. Better forage will.
- A haynet before transport and before training. Those are the two moments when acid exposure rises fastest, and a stomach with forage in it is a protected one.
- Consistency matters as much as quantity. Hay with wildly different sugar content from bale to bale makes an already sensitive horse harder to manage.
None of this asks for a different life for the horse. It asks for a different look at what's in the hay rack at six in the morning, and what's on board before the ramp goes up. Small, for whoever manages the day. Significant, for the horse whose stomach has been quietly fighting itself while nobody noticed, until it bleeds.
Curious what your own horse's ration actually looks like? Run the numbers with the free feeding calculator.
