Ulcers in Horses: Understanding, Diagnosing, and Managing Equine Gastric Ulcer Syndrome

Gastric ulcers are one of the most common health problems affecting horses today. They can cause discomfort, behavioural changes, poor performance, and even long-term digestive complications if left untreated. As a horse owner, understanding how and why ulcers develop, and what you can do to prevent and manage them, is vital for maintaining your horse’s health and wellbeing.

This guide explains everything you need to know about ulcers in horses, from causes and symptoms to diagnosis, treatment, and prevention.

What Are Ulcers in Horses?

Equine ulcers, more formally known as Equine Gastric Ulcer Syndrome (EGUS), occur when the protective lining of the stomach becomes eroded by stomach acid. Horses produce stomach acid continuously, even when they are not eating, which makes them especially prone to this condition.

There are two main types of ulcers in horses:

1. Squamous ulcers – Found in the upper, non-glandular portion of the stomach. These are the most common type and usually result from prolonged exposure of the stomach lining to acid.
2. Glandular ulcers – Found in the lower, glandular portion of the stomach. These are less common but can be more difficult to treat because they involve the acid-producing region of the stomach.

A third type, colonic ulcers, can develop further along the digestive tract, but these are less well understood and often associated with stress or prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs).

The Horse’s Stomach: Why It’s Prone to Ulcers

To understand why ulcers are so common in horses, it helps to know how their stomach works.

The equine stomach is divided into two sections:

• The non-glandular (squamous) area, which has little natural protection against stomach acid.
• The glandular area, which secretes mucus and bicarbonate to protect itself from acid.

In their natural state, horses graze for 16–18 hours a day, constantly producing saliva that helps buffer stomach acid. However, when horses are stabled, exercised, or fed large, infrequent meals, acid continues to be produced but without sufficient saliva or forage to neutralise it. This leaves the stomach lining vulnerable to acid damage.

Causes of Ulcers in Horses

There is no single cause of ulcers; rather, a combination of factors increases the risk. The main contributing causes include:

• Fasting or irregular feeding – Long periods without forage allow acid to build up.
• High-grain diets – Starch fermentation increases acid levels.
• Stress – Transport, competition, or social stress can alter acid production and reduce appetite.
• Intense exercise – Increases abdominal pressure, pushing acid upwards into unprotected areas of the stomach.
• Stall confinement – Reduces natural grazing and movement.
• Use of NSAIDs – Prolonged use of drugs like phenylbutazone can reduce the stomach’s protective mucus layer.
• Illness or pain – Horses under systemic stress are more prone to gastric irritation.

Signs and Symptoms

Ulcers can be subtle and vary from horse to horse. Some horses show obvious discomfort, while others may only display small behavioural changes. Common signs include:

Physical Signs

• Poor appetite or slow eating
• Weight loss or poor condition
• Dull coat
• Recurrent colic, especially mild or after meals
• Poor performance or reluctance to move forward under saddle

Behavioural Signs

• Irritability or aggression when girthing
• Resistance during riding, especially when collecting or bending
• Grinding teeth or excessive yawning
• Decreased interest in work or jumping
• Restlessness or lying down frequently

In Foals

Foals can also develop ulcers, particularly if under stress or separated from their dam. Symptoms include teeth grinding, drooling, diarrhoea, or lying on their backs (to relieve discomfort).

Diagnosis

A definitive diagnosis of gastric ulcers can only be made through gastroscopy, a procedure where a flexible endoscope is passed into the horse’s stomach to visually inspect the lining.

During gastroscopy:

• The horse is fasted overnight.
• Sedation is administered.
• The veterinarian inserts the scope through the nostril, down the oesophagus, and into the stomach.
• The stomach lining is examined for signs of erosion or ulceration.

The severity of ulcers is then graded on a scale from 0 to 4:

• Grade 0 – Normal, healthy stomach lining.
• Grade 1 – Mild redness or roughened areas.
• Grade 2 – Small, superficial ulcers.
• Grade 3 – Large or deep ulcers.
• Grade 4 – Extensive, bleeding lesions.

Treatment Options

Treatment focuses on reducing stomach acidity, promoting healing, and addressing underlying causes.

1. Acid Suppression

Omeprazole is the most effective and widely used medication for treating gastric ulcers in horses. It works by reducing acid production in the stomach and allowing the lining to heal. It is available in several formulations under veterinary prescription.

• GastroGard (full-strength omeprazole paste) – the gold standard for treatment.
• UlcerGard – a preventative, lower-dose formulation for horses under stress.

Other medications that may be used include:

• Ranitidine – a less potent acid reducer, used less frequently today.
• Sucralfate – coats the stomach lining and protects it from acid, often used in glandular ulcers.
• Misoprostol – used for glandular or NSAID-related ulcers to enhance protective mucus production.

2. Dietary Management

Proper feeding is crucial for both healing and prevention:

• Provide free-choice hay or pasture at all times to keep the stomach buffered.
• Use alfalfa hay, which has a natural buffering effect due to its calcium content.
• Feed small, frequent meals rather than two large feeds a day.
• Avoid high-starch, high-sugar feeds, opt for fibre-based diets instead.
• Provide access to clean water at all times.

3. Reduce Stress and Environmental Triggers

• Maximise turnout time and minimise stall confinement.
• Establish a consistent routine for feeding, exercise, and travel.
• Reduce exposure to stressors such as abrupt changes in herd dynamics or feed.
• Use slow feeders or hay nets to encourage natural grazing behaviour.

4. Supportive Care

• Add supplements containing pectin-lecithin complexes, magnesium hydroxide, or probiotics to support gut health.
• Monitor for recurring symptoms and adjust diet or management as needed.

Prevention

Preventing ulcers is often easier than treating them. Consistent management and thoughtful feeding practices can make a huge difference.

• Keep forage available at all times to prevent acid build-up.
• Avoid prolonged fasting or gaps between meals.
• Minimise high-grain feeds and include more roughage.
• Provide alfalfa hay before exercise to help buffer stomach acid.
• Manage stress with regular turnout and predictable routines.
• Administer preventative omeprazole during high-stress periods such as travel or competition.
• Avoid overuse of NSAIDs and always follow veterinary guidance when they are prescribed.

Prognosis

Most horses respond very well to treatment, with noticeable improvements in behaviour and condition within weeks. However, relapse is common if management changes are not maintained. Regular monitoring, dietary consistency, and attention to stress levels are key to long-term gastric health.

Conclusion

Ulcers in horses are a widespread yet preventable problem. They arise from a combination of diet, management, and stress-related factors that disrupt the horse’s natural digestive balance. Recognising the signs early and working closely with your vet to implement a comprehensive treatment and prevention plan can make a significant difference to your horse’s comfort, performance, and overall wellbeing.

By providing constant access to forage, reducing stress, and feeding thoughtfully, you can greatly reduce the risk of ulcers and keep your horse’s digestive system healthy for years to come.