Ventriculus (Gaster)
The equine stomach is relatively small (8-15 liters capacity, approximately 8-10% of the total GI tract volume), reflecting the horse's evolutionary adaptation as a continuous grazer rather than a meal feeder. It is divided by the margo plicatus into a proximal non-glandular (squamous) region and a distal glandular region. Gastric acid is secreted continuously; even when the horse is not eating; which is why prolonged fasting predisposes to squamous ulceration. The powerful cardiac sphincter and the oblique angle of esophageal entry prevent vomiting, meaning the stomach can rupture before contents can be expelled retrograde.
The equine stomach is remarkably small (~8-15 liters, only 8-10% of total GI capacity) for the horse's size. It has two distinct regions: the non-glandular squamous mucosa (proximal, stratified squamous epithelium providing no acid protection) and the glandular mucosa (distal, secretes HCl, pepsin, and mucus). The margo plicatus is the dividing line. Gastroscopy (3-meter endoscope) after 12-16 hours fasting is the gold standard for diagnosis of EGUS.
Equine Gastric Ulcer Syndrome (EGUS) refers to ulceration of the stomach lining and is subdivided into Equine Squamous Gastric Disease (ESGD), affecting the non-glandular upper stomach, and Equine Gla
Full-thickness rupture of the stomach wall; invariably fatal. May result from severe gastric distension (grain overload, primary gastric impaction, ileus with fluid accumulation). Unique to horses bec
Accumulation of dehydrated, compacted feed material in the stomach. Associated with poor dentition, persimmon ingestion, and inadequate water intake.
The most common gastric neoplasm in horses, arising from the squamous mucosa of the non-glandular region. Usually diagnosed late due to non-specific signs.
Narrowing of the pyloric outflow tract, which may be congenital (foals) or acquired (chronic ulceration, neoplasia).
Equine Gastric Ulcer Syndrome (EGUS) refers to ulceration of the stomach lining and is subdivided into Equine Squamous Gastric Disease (ESGD), affecting the non-glandular upper stomach, and Equine Glandular Gastric Disease (EGGD), affecting the lower glandular portion. ESGD is very common in athletic horses, with prevalence rates of 50 to 90% reported in some populations. ## What it is The equine stomach is divided into two regions: the squamous (non-glandular) portion in the upper part and the glandular portion in the lower part. The squamous region lacks the protective mucus and bicarbonate layer found in the glandular region, making it more susceptible to acid damage. Prolonged exposure to stomach acid, reduced saliva production during exercise, and stress are major contributors to squamous ulcers. Glandular ulcers have a different pathophysiology and are often linked to stress, NSAID use, and other factors. Horses are continuous grazers by nature. When they are fed intermittent meals or exercised on an empty stomach, acid can splash onto the unprotected squamous mucosa, leading to ulceration. ## Signs and symptoms - Poor appetite or picky eating - Poor body condition or dull coat - Recurrent low-grade colic, especially after eating - Girthiness or resistance to saddling - Behavioral changes or decreased performance - Grinding teeth or signs of discomfort - In severe cases, weight loss and lethargy ## Causes and risk factors Risk factors for EGUS include intense training and competition, intermittent feeding, high-grain diets, stress (transport, competition, changes in routine), and NSAID administration. Squamous ulcers are strongly associated with exercise and periods without forage. Glandular ulcers appear more related to stress and disruption of the stomach's natural protective mechanisms. ## How it is diagnosed Gastroscopy (endoscopic examination of the stomach) is the only definitive way to diagnose EGUS and determine the location, severity, and type of ulcers. Horses are typically fasted before the procedure. In some cases, a presumptive diagnosis is made based on clinical signs and response to treatment, but gastroscopy is strongly recommended for accurate diagnosis and monitoring of treatment response. ## Treatment and management Treatment depends on the type and severity of ulcers. For squamous ulcers, the mainstay is acid suppression using omeprazole, often combined with dietary management (increased forage, reduced grain). Glandular ulcers may require longer treatment courses and sometimes additional medications such as sucralfate. Management changes, including more frequent feeding, reduced stress, and avoiding NSAIDs when possible, are essential for long-term control and prevention of recurrence. ## When to call the vet Contact your veterinarian if your horse shows signs of poor appetite, recurrent colic, girthiness, or declining performance. Gastroscopy is the best way to confirm the presence and severity of ulcers and to guide appropriate treatment. ## Prevention Prevention focuses on management changes that support natural stomach function: providing constant access to forage, feeding smaller more frequent meals, reducing stress where possible, and using protective medications during high-risk periods such as intense training or transport. ## Frequently asked questions **How common is EGUS in horses?** Very common. Studies show 50 to 90% of performance horses may have squamous ulcers, with glandular ulcers also frequently diagnosed. **Can ulcers heal on their own?** Mild cases may improve with management changes alone, but most require medication for reliable healing, especially glandular ulcers. **Do all horses with ulcers show obvious signs?** No. Many horses have ulcers without obvious clinical signs, which is why gastroscopy is important in horses with subtle performance issues. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Poor appetite or picky eating; poor body condition or dull coat; recurrent low-grade colic, especially after eating; girthiness or resistance to saddling; behavioral changes or decreased performance; grinding teeth or signs of discomfort; in severe cases, weight loss and lethargy
Full-thickness rupture of the stomach wall; invariably fatal. May result from severe gastric distension (grain overload, primary gastric impaction, ileus with fluid accumulation). Unique to horses because they cannot vomit. Signs include: Acute severe colic followed by sudden apparent improvement (pain relief when stomach ruptures); rapid cardiovascular collapse; peritonitis; death within hours
Accumulation of dehydrated, compacted feed material in the stomach. Associated with poor dentition, persimmon ingestion, and inadequate water intake. Signs include: Chronic low-grade colic; anorexia; weight loss; large stomach visible on ultrasound; nasogastric reflux may be minimal (food too solid to reflux)
The most common gastric neoplasm in horses, arising from the squamous mucosa of the non-glandular region. Usually diagnosed late due to non-specific signs. Signs include: Progressive weight loss; chronic low-grade colic; intermittent fever; anemia; hypoproteinemia; identified on gastroscopy as irregular, raised, ulcerated mass
Narrowing of the pyloric outflow tract, which may be congenital (foals) or acquired (chronic ulceration, neoplasia). Signs include: Chronic colic after eating; bruxism (teeth grinding); ptyalism; gastric distension; large volume of nasogastric reflux
The equine stomach is remarkably small (~8-15 liters, only 8-10% of total GI capacity) for the horse's size. It has two distinct regions: the non-glandular squamous mucosa (proximal, stratified squamous epithelium providing no acid protection) and the glandular mucosa (distal, secretes HCl, pepsin, and mucus). The margo plicatus is the dividing line. Gastroscopy (3-meter endoscope) after 12-16 hours fasting is the gold standard for diagnosis of EGUS.
See the Stomach on our interactive 3D horse model. Open 3D Model