Gastric Ulcers in Horses: Recognizing and Preventing

More than 60% of sport horses have gastric ulcers, and in a 2015 review pooling data across UK competition disciplines the figure reached 64% of nearly 500 horses tested [1]. That number surprises most owners when they first hear it, because many of these horses never show the obvious signs we associate with a stomach problem. They perform poorly, girth up badly, or lose condition gradually. By the time someone thinks to investigate the stomach, ulcers have often been present for months.

How the horse's stomach gets into trouble

The horse evolved to graze continuously. The stomach produces acid around the clock regardless of whether food is present. In a natural grazing pattern, that acid is constantly buffered by saliva and the physical presence of forage. Saliva production is highest when the horse is chewing roughage. Take away continuous access to hay or grass, and the acid sits in an insufficiently buffered environment.

The stomach has two distinct regions. The glandular mucosa in the lower half is built to withstand acid. The squamous mucosa in the upper half is not. Most ulcers form at that junction, where acid pools when the horse is stabled, worked on an empty stomach, or simply fed too little roughage too infrequently.

Transport adds a specific mechanism worth knowing. Research on mares transported for several hours found that bile acids reflux from the intestine back into the stomach, and gastric emptying is disrupted [2]. The result is direct damage to the gastric mucosa from bile exposure, which is a different problem from simple acid accumulation. That distinction matters more than most owners realise when they're planning a show season.

Recognising the signs

The symptoms are frustratingly non-specific. Decreased appetite, gradual weight loss, a dull coat, and recurring low-grade colic are the most common presentation in adult horses. Poor performance is often the first thing an owner notices, usually before any obvious discomfort. In foals the picture is different: teeth grinding and excessive yawning are characteristic signs.

Girthiness is worth calling out separately. A horse that bites, pins ears, or shows pain responses when being girthed has often been labelled difficult or behavioural. In clinical practice, girthiness that appears or worsens over time is a reason to consider gastric ulcers until proven otherwise.

Diagnosis is by endoscopy. There is no reliable way to confirm ulcers from symptoms alone, and treatment is long enough and expensive enough that I would always recommend scoping before committing to a protocol. A positive response to acid-suppressing medication is sometimes used as a surrogate diagnostic, but it can miss hindgut problems and does nothing to identify the underlying cause.

Prevention: what actually changes the outcome

Forage first, always

A 600 kg horse should have access to a minimum of 9 to 12 kg of forage dry matter per day, ideally closer to 2% of bodyweight. Slow feeders and hay nets extend eating time and keep saliva production consistent throughout the day. This is the single most effective intervention. Everything else is secondary.

The reason is mechanical as much as chemical. A horse producing saliva continuously is buffering acid continuously. Reducing that buffer by restricting hay to set meal times, particularly overnight, creates an extended acid exposure window that no supplement or medication fully compensates for [5].

The case for alfalfa

Alfalfa is high in calcium, which directly neutralises stomach acid. A controlled feeding trial found that horses switched from grass hay to an alfalfa hay and grain diet showed a higher gastric fluid pH and fewer, less severe ulcers [6]. It has the practical advantage of being highly palatable for horses that have gone off their feed. Choose a product without added molasses. It is not a treatment for established ulcers, but it is a meaningful part of a prevention diet.

Limit concentrate feeding

For a 500 kg horse, the practical ceiling for concentrate is around 2.5 kg per day. More than that, particularly in single large meals, drives rapid gastric acid production without adequate buffering. Where sport performance demands higher caloric density, spreading concentrate across a minimum of four feedings and ensuring roughage is available before and after each one reduces the peak acid load [7]. Leave at least six hours between concentrate meals.

Transport management

Given what we know about bile reflux during transport, the logic is straightforward: keep the horse eating. Offer hay and water until just before loading. If the journey is long, hay access during transit reduces both the physiological stress and the direct mucosal damage from prolonged fasting in a moving vehicle [2].

Reducing stress

Stress is not a vague contributing factor. It has direct physiological effects on gastric motility and acid secretion. Horses kept in social isolation, in stalls without visual contact with other horses, or in high-turnover competition environments consistently show higher ulcer rates. Where management allows it, turnout with companions is part of the prevention protocol, not a luxury.

Supporting the gut long-term

Diet and management cover the structural causes. Gut flora and mucosal integrity are a separate layer. Pre- and probiotics that specifically support the gastric mucosa can be a useful addition for horses in demanding competition schedules or those recovering from a treatment course.

Treatment when ulcers are confirmed

Medication for confirmed ulcers means acid suppression, typically with omeprazole, for a minimum of four weeks. Medication alone is not sufficient. Without changing the feeding pattern and management conditions that caused the ulcers, recurrence rates are high.

The full protocol is medication plus dietary adjustment plus, where appropriate, targeted supplementation. Scoping at the end of the treatment period confirms resolution before stopping medication. Skip that follow-up scope, and if symptoms return you lose several weeks of useful information about whether the treatment was adequate or the management changes were sufficient.