Equine Gastric Ulcers: Why 50-90% of Horses Have Them

Your Horse Probably Has Ulcers Right Now

I want you to sit with an uncomfortable statistic for a moment. Depending on which study you read, somewhere between 60 and 90 percent of performance horses have gastric ulcers. Even among horses living what we would consider a relaxed life — pasture-kept, light riding — the prevalence sits around 50 percent. That means if you have two horses in your field right now, odds are at least one of them has ulcers.

In my years of equine practice, I have scoped hundreds of horse stomachs. What still surprises me is how many owners are genuinely shocked when I show them the angry, eroded lining on the monitor. Their horse "seemed fine." And that is exactly the problem with Equine Gastric Ulcer Syndrome, or EGUS — most horses do not scream about it. They whisper.

Why the Horse Stomach Is Designed to Fail

To understand why ulcers are so absurdly common, you need to understand one fundamental fact about equine digestion: your horse's stomach produces hydrochloric acid continuously. Not just when food arrives — all the time, 24 hours a day, whether the stomach is full or completely empty.

In nature, this system works beautifully. Wild horses graze 16 to 18 hours per day. There is almost always a fiber mat sitting in the stomach, absorbing acid, buffering the pH, and protecting the stomach lining. The saliva produced by all that chewing contains bicarbonate, a natural antacid. The system is elegant when used as designed.

Now consider what we do to domesticated horses. We feed two large meals a day, sometimes three if we are feeling generous. Between meals, the stomach sits empty — sometimes for six, eight, even twelve hours. But the acid does not stop. It pools. It splashes. And it burns.

Squamous vs. Glandular: Two Different Diseases

The horse stomach has two distinct regions, and each ulcerates for different reasons. The upper third is lined with squamous epithelium (non-glandular mucosa) — essentially the same type of tissue that lines your esophagus. This tissue has no protective mucus layer. When acid splashes up from the lower stomach, the squamous region takes the hit directly. This is where the majority of ulcers form, and this is the region most affected by meal timing and exercise.

The lower two-thirds is glandular mucosa — tissue that actually produces the acid and is normally protected by a thick mucus and bicarbonate barrier. Glandular ulcers are less common but tend to be more stubborn to treat. They are associated with NSAID use (phenylbutazone, flunixin), stress, and possibly bacterial involvement. The clinical significance here is that squamous and glandular ulcers may require different treatment protocols, and I will get to that.

Signs Your Horse May Be Telling You About Ulcers

Here is where EGUS gets tricky. Horses are stoic animals, and ulcer signs can be maddeningly subtle. I have seen Grade 3 and 4 ulcers (significant erosion and bleeding) in horses that were still eating, still performing, still looking "fine" to their owners.

That said, there are patterns. Watch for these:

• Poor appetite or picky eating — especially reluctance to finish grain meals, or eating hay but refusing concentrates
• Weight loss or poor body condition despite adequate calories — the horse that should be gaining but is not
• Girthiness — flinching, pinning ears, swishing tail, or biting when you tighten the girth. This is one of the most common owner complaints I hear
• Behavioral changes under saddle — resistance to leg aids, reluctance to canter, bucking or bolting that is new and out of character
• Dull, rough coat that does not respond to deworming or dietary changes
• Recurrent mild colic — subtle signs like flank-watching, lying down more than usual, or mild discomfort after eating
• Attitude changes — a previously pleasant horse that becomes cranky, girthy, or withdrawn

None of these signs are specific to ulcers. Every single one of them could be caused by something else entirely. That is why I tell owners: if your horse is showing several of these signs, ulcers belong on the differential list, but we need to confirm it.

Diagnosis: Gastroscopy Is the Only Answer

I am going to be blunt here. There is no blood test for gastric ulcers. There is no fecal test. There is no "ulcer panel." Anyone selling you a diagnostic test that does not involve a camera going into the stomach is selling you wishful thinking.

Gastroscopy — passing a three-meter endoscope through the nostril, down the esophagus, and into the stomach — is the only way to definitively diagnose EGUS, grade its severity, and determine whether you are dealing with squamous ulcers, glandular ulcers, or both. The procedure requires the horse to be fasted (12 to 18 hours, water pulled 4 to 6 hours before) and lightly sedated. It takes about 15 to 20 minutes, and the horse goes home the same day.

I understand that scoping costs money — typically $250 to $500 depending on your region. But consider this: a 28-day course of GastroGard runs $800 to $1,200. If you are going to spend that money on treatment, you should know what you are treating. I have scoped horses that owners were convinced had ulcers and found a perfectly healthy stomach. I have also scoped horses "just to check" and found bleeding Grade 4 ulcers. The scope does not lie.

Treatment: What Actually Works

The gold standard for squamous gastric ulcers is omeprazole, a proton pump inhibitor that suppresses acid production at its source. The FDA-approved formulation is GastroGard (treatment dose) and UlcerGard (prevention dose) — both are the same drug, just different concentrations per syringe.

The Protocol That Heals

For squamous ulcers, the evidence-based protocol is:

• Treatment phase: Omeprazole 4 mg/kg once daily for a minimum of 28 days. For a 500 kg (1,100 lb) horse, that is one full tube of GastroGard per day.
• Re-scope at day 28: Confirm healing before tapering. I cannot overstate how important this step is — stopping treatment based on "he seems better" without confirming mucosal healing leads to rebound ulceration.
• Taper: Gradually reduce the dose over 7 to 14 days rather than stopping abruptly. Abrupt cessation can cause rebound acid hypersecretion.

For glandular ulcers, treatment gets more complicated. Omeprazole alone often is not enough. I typically combine omeprazole with sucralfate (a mucosal protectant that binds to ulcerated tissue) at 20 mg/kg two to three times daily. Glandular ulcers may require 8 to 12 weeks of treatment, and healing rates are lower than squamous. Some cases also benefit from misoprostol, though that drug has handling precautions (it can cause abortion in pregnant mares and must be handled carefully by women of childbearing age).

Why Compounded Omeprazole Often Fails

I see this constantly. An owner wants to save money — understandably — and gets compounded omeprazole from a pharmacy at a fraction of the GastroGard price. Three weeks later, the horse is no better, and they are frustrated.

Here is the problem. Omeprazole is an extremely unstable molecule. It degrades rapidly when exposed to stomach acid — the very acid it is supposed to suppress. GastroGard uses a proprietary enteric coating and paste formulation that protects the drug through the acidic stomach so it can be absorbed in the small intestine. Most compounded formulations do not replicate this protection adequately. Multiple studies have shown that compounded omeprazole products vary wildly in potency and bioavailability, with some containing as little as 30 percent of the labeled dose by the time they reach the horse.

Am I saying every compounded product is worthless? No. Some compounding pharmacies do excellent work. But the consistency issue is real, and if your horse is not responding to compounded omeprazole, switch to the FDA-approved product before you conclude that "omeprazole doesn't work."

Prevention: This Is Where You Win

Treating ulcers is expensive and time-consuming. Preventing them is cheaper, more effective, and better for your horse. Here is what the evidence supports:

Forage, Forage, Forage

The single most important preventive measure is unlimited access to forage. Hay. Grass. Something for the horse to chew. The goal is to never let the stomach sit empty for more than four hours. If you cannot provide free-choice hay (some easy keepers will become obese), use slow-feed hay nets to extend eating time, feed smaller meals more frequently, or provide a low-calorie forage like mature grass hay or straw (mixed with regular hay so the horse does not fill up on straw alone).

The Alfalfa Buffer

Alfalfa hay has a higher calcium and protein content than grass hay, and both act as natural acid buffers. Studies have shown that feeding alfalfa hay or an alfalfa-based chaff before exercise significantly reduces the severity of squamous ulcers. I recommend feeding a flake of alfalfa or a handful of alfalfa chaff 30 minutes before riding. It is cheap, effective, and easy.

Destroy the "No Hay Before Riding" Myth

I hear this constantly: "I don't feed my horse before riding because he'll get colic." This advice is not only wrong — it is actively harmful. When a horse exercises on an empty stomach, the acid in the lower (glandular) region splashes up onto the unprotected squamous mucosa. Every stride of trot and canter creates a wave of acid washing over tissue that has no defense against it. Feeding a small amount of forage before work creates a fiber mat that physically blocks acid splash. Feed your horse hay before you ride. A flake of hay or a handful of chaff is not going to cause colic. An empty, acid-bathed stomach just might cause ulcers.

Management Adjustments

• Reduce stall time: Horses in stalls ulcerate at higher rates than horses with turnout. Social isolation, boredom, and restricted movement all contribute to stress-related acid production.
• Limit NSAID use: Phenylbutazone and flunixin are essential tools, but chronic use damages the glandular mucosa. Use the lowest effective dose for the shortest duration. If your horse needs daily bute, talk to your vet about alternatives.
• Manage stress: Trailering, competition, herd changes, intense training — all increase ulcer risk. During high-stress periods, consider preventive-dose omeprazole (UlcerGard at 1 mg/kg).
• Feed concentrates in small, frequent meals: Large grain meals stimulate acid production. If your horse needs concentrates, split the ration into three or four smaller feedings.

The Bottom Line

Gastric ulcers are not a disease of bad horsemanship. They are a consequence of the fundamental mismatch between how we manage horses and how their digestive systems evolved. Even the best-cared-for horse can develop EGUS. What separates good management from great management is recognizing the risk, knowing the subtle signs, and acting decisively when your horse tells you something is wrong.

If your horse is girthy, cranky, losing weight, or just not himself — scope first, treat second. Do not guess. Do not rely on supplement marketing. Get a camera in there and find out what you are dealing with. Your horse's stomach has been talking to you. It is time to listen.