The gastric ulcer conundrum
By Hannah Elliott, monogastric technical manager, Lallemand Animal Nutrition UK & Ireland.
Gastric ulcers, collectively Ulcer Syndrome (EGUS), are prevalent in the equine community. Triggered by stress, diet, and some management practices, these lesions compromise welfare and performance. Early diagnosis and targeted treatment are essential for maintaining equine health and competitive longevity.
Stomach anatomy and physiology
The horse’s digestive anatomy plays a central role in its vulnerability to gastric ulcers. The equine stomach is relatively small, holding approximately 12 litres and accounting for only 8% of the total digestive tract volume (Merritt et al.,2013). It is divided into two distinct regions by a visible ridge called the margo plicatus:
The squamous (non-glandular)region: This upper third of the stomach is lined with a tissue similar to the oesophagus and lacks protective secretions.
The glandular region: This lower portion contains glands that secrete hydrochloric acid, pepsin, and lipase for digestion, as well as bicarbonate-rich mucus that protects the stomach lining.
Gastric ulcers
ulcers using the 0-4 scoring
system from the Equine
Gastric ulcers are erosions of the stomach mucosa, caused by an imbalance between acid and natural defences such as the mucous layer, bicarbonate, good blood flow and cell renewal. The severity of an ulcer depends on its size, the number of lesions, degree of haemorrhaging and the presence of necrotic areas. There are two types of EGUS in horses:
Equine Squamous Gastric Disease (ESGD) are ulcers in the squamous region. These are most common due to its lack of protective mechanisms and often linked to diet, exercise and management.
Equine Glandular Gastric Disease (EGGD) are ulcers in the glandular region. These are less understood but involve impaired mucosal protection and are often associated with stress, non-steroidal anti-inflammatory drug(NSAID) use, and systemic pain.
Prevalence of EGUS
SEIB reports that gastric ulcers were the most frequent insurance claim between 2020 and 2025, and the second most expensive. Performance horses fed high concentrate, low forage meals are typically at most risk of gut ulcers, with one study reporting that the highest prevalence of ESGD occurs in thoroughbred racehorses, with 80–100% suffering from ESGD within 2–3 months of race training (Sykes et al., 2015).
However, feral and young Icelandic horses on pasture have also been shown to have a varying prevalence of both ESGD and EGGD, suggesting that natural diets and environments alone do not eliminate the risk (Ward et al., 2015, Luthersson et al., 2022).
Although some breeds or groups of horses may be more prone to gastric ulcers, every horse is different. Some horses show no symptoms at all, while others display subtle changes that owners might not detect. Behavioural clues can include development of stereotypies, signs of discomfort, resistance to being tacked up or ridden, and changes in appetite. In many cases, gastric ulcers are only discovered and identified when a horse shows signs of colic or other digestive discomfort.
Feeding practices and their impact
When acid levels get too high, the stomach releases substances like prostaglandin E2 to enhance protective mechanisms such as enhanced mucous bicarbonate secretion to neutralise the acid. However, this feedback mechanism is not sufficient on its own and leaving the stomach empty for long periods exposes the mucosa to unbuffered acid, increasing the risk of ulceration. It can also be disrupted by medications such as phenylbutazone (Bute), a commonly used non-steroidal anti-inflammatory drug (NSAID).
Feeding rough or sharp forages has also been implicated by causing irritation and mechanical damage to the stomach lining. Due to this, poor dentition is a risk factor for EGGD due to insufficient grinding and breakdown of fibre particles. Equally, overly eager eaters may not chew forage sufficiently and so techniques to slow down feeding can be valuable. Horses produce 3 times the amount of saliva when consuming 1kg forage vs. 1kg concentrate. Providing enough forage per day - at least 1.5kg per 100kg of body weight - generates enough sodium bicarbonate in saliva to buffer the constant acid production within the stomach, particularly during hours of activity and increased movement.
Horses are grazers, biologically adapted to consume large amounts of high-fibre, low-starch diets over a prolonged period of time for gut fill, and deviations from this can significantly increase ulcer risk. High-starch diets can ferment in the stomach, producing volatile fatty acids (VFAs) such as lactic, acetic, propionic and butyric acids, which further lower pH. Combined with reduced chewing—and therefore less natural buffering—the faster gastric emptying caused by concentrate meals (due to their smaller particle size compared to forage) shortens the time available for buffering and increases acid exposure, both of which are risk factors for ESGD. Low water intake is also associated with an increase in all equine gut ulcers. (Sykes et al., 2015).
Exercise and stress as contributing factors
Physical activity, particularly intense exercise, can exacerbate ulcer formation and exercising more than 4-5 times per week has been implicated in increased risk of EGGD. Blood flow can be diverted away from the stomach during activity, reducing nutrient flow to existing ulcers and compromising the stomach’s natural protective mechanisms. Abdominal contractions during exercise also compress the stomach, allowing acid to splash into the unprotected squamous region and increasing the risk of ESGD. Due to this, a good fibre mat to prevent gastric juice splashing and ensuring horses are fed fibre before exercise can limit the risk for ESGD.
Stress - whether from confinement, transport, competition, or changes in routine - also plays a significant role as stress hormones can reduce blood flow to the stomach lining and impair its ability to heal existing gastric ulcers. A new study by Haliwell et al., 2025 found that lameness, back pain and stress are risk factors for EGGD, as glandular ulcers can be a secondary condition to a source of pain.
Treatment and management recommendations
Currently, the primary treatment for gastric ulcers is Omeprazole, a proton pump inhibitor that reduces acid production. Although pharmacological intervention improves short-term effects, prolonged use may affect metabolism and reduced nutrient absorption. If management practices and causative risk factors aren’t corrected in conjunction with treatment, ulcers will reappear. Other therapies and supplements, such as a Lactobacillus postbiotics in conjunction with management changes are being used successfully with horses and ponies who are prone to EGUS, or after Omeprazole. They can help with inflammation, assist in epithelial cell repair and support blood flow. The British Equine Trade Association (BETA) have launched a gastric ulcer approval mark through collaboration with the Veterinary Medicines Directive (VMD), aimed at helping owners choose suitable feed stuffs. It only applies to feed, be it concentrate or high/ chopped fibre feeds and looks at the sugar, starch and overall energy of the feed and whether it contributes to a balanced diet.
The following strategies can help reduce gut ulcer risk factors:
- Feed at least 1.5 kg of forage per 100 kg of body weight daily.
- Ensure forage (fibre) is available and eaten before exercise
- Maximise chewing and eating time (and saliva production) by offering long-stem forage
- Check dental health regularly to ensure effective mastication
- Avoid prolonged fasting and feed no more than 2g starch/ kg body weight per day over more than 2 meals per day
- Provide constant access to clean water during turnout, transport and stabling
- Monitor your horse for signs of pain, stress and discomfort
- Give your horse 2 days of rest per week.
