Equine Gastric Ulcer Syndrome (EGUS) is a common problem in horses of all ages and disciplines. Ulcers are wounds in the lining of the stomach caused by acid. Studies of various populations of horses have found the prevalence of EGUS to be quite high.

Discipline % of population affected
Flat Racing 92
Harness Racing 86
Saddle Seat 82
Reining 76
Cutting 69
Show Jumping 67
Eventing 62
Barrel Racing 51
Dressage 44

Reports found that 25 to 50 percent of foals have ulcers.

So why do so many horses have gastric ulcers?

The short answer is how we manage them; how we feed them, how we train them, how we keep and transport them.

Horses evolved to be nomadic grazers. Their gastrointestinal (GI) tracts are designed to have fiber (grass, weeds, leaves) in them at all times. A horse’s stomach continuously secretes acid (mainly hydrochloric), whether there is food in it or not. An adult horse can produce up to 16 gallons of acidic fluid each day. In nature, horses are continuously grazing, so the stomach is rarely empty. This food in the stomach, along with bicarbonate in saliva, helps to neutralize the stomach acid. In addition, the movement of continuous walking promotes GI motility and keeps food and acid moving out of the stomach. Horses begin to secrete stomach acid as young as two days of age and the acidity of their stomach secretions is usually very high. In the adult horse, the pH of gastric contents ranges from 1.5 to 7.0, depending on region measured. A near neutral pH can be found in the dorsal portion of the esophageal region (saccus caecus) near the lower esophageal sphincter, whereas, more acidic pHs can be found near the margo plicatus (3.0-6.0) and in the glandular region near the pylorus (1.5-4.0)

Stomach anatomy

The horse stomach is divided into two distinct regions, the esophageal or non-glandular region and the glandular region. The esophageal region or squamous mucosa covers approximately one-third of the equine stomach, is void of glands, and is covered by stratified squamous epithelium similar to the esophagus. The glandular region covers the remaining two-thirds of the stomach and contains glands that secrete hydrochloric acid, pepsin, bicarbonate and mucus.

The glandular mucosa is protected from acid damage by proper blood flow, bicarbonate buffering of acid, and mucus that forms a protective layer over the mucosa. Ulcers can be present in either the squamous or glandular portion of the stomach, but are more common in the squamous portion at the margo plicatus. This area is almost constantly exposed to acid, pepsin, bile acids and organic acids. Ulcers in the glandular mucosa are usually due to disruptions in blood flow to the area and decreased mucus and bicarbonate production.

Causes of EGUS

EGUS is a complicated syndrome with many causative factors.

Fasting or intermittent feeding have been shown to consistently induce gastric ulceration in horses. The empty stomach is exposed to acids which can attack the defenseless squamous mucosa and overwhelm the defenses of the glandular mucosa.

Diets high in concentrates have also been shown to induce ulcers. The carbohydrate rich grains are fermented to volatile fatty acids (VFA). These VFA enter the cells of the squamous mucosa, cause the cells to swell and die, cause inflammation, eventually ulceration.

Exercise causes increased intra-abdominal pressure in horses resulting gastric compression, pushing acidic contents into the proximal, squamous-lined region of the stomach. Increased duration of acid exposure directly related to daily duration of exercise may be the reason that squamous lesions tend to develop or worsen when horses are in intensive training programs. Exercise may also have an inhibitory effect on gastric emptying.

Anything that causes delayed gastric emptying will predispose a horse to gastric ulcers. This is most common in foals with duodenal outflow obstructions, but can occur in adults with ileus due to any number of conditions.

In foals, gastric ulceration may be related to desquamation or “shedding” of the squamous epithelium of the stomach. Desquamation of the squamous mucosa, occurs in 80% of foals up to 35 days of age. In a study of rats, it was found that the loss of epithelial cells along the margo plicatus resulted in the increased susceptibility of this region to acid injury. Also, acid injury to this region resulted in a delay in re-epithelialization. Delayed re-epithelialization could result in acid injury of the deeper layers from hydrochloric acid and lead to gastric ulceration.

Housing, Trailering, NSAIDs

Horses that live outside and are allowed to graze at will have fewer ulcers than horses that are stalled. One study found that horses that were brought into stalls after living outside developed gastric ulcers, some in as little as 24 hours.

Trailering horses causes stress that leads to gastric ulcers. An interesting fact found during this study was that not only did the horses that were transported during the study develop ulcers, but so did those horses that were left behind. Seems as though everyone got stressed. This stress can lead to increased cortisol levels, decreased blood flow to the stomach, and reduced hay intake, all of which contribute to gastric ulceration.

Non-steroidal anti-inflammatory drugs (NSAIDs) are notorious for causing stomach ulcers in all species. They reduce protective prostaglandins, decrease mucus production, and interfere with proper blood flow to the stomach.

Signs of EGUS

Horses will display a variety of clinical signs in response to gastric ulcers. These can range from being off feed to knocking down rails in the jump off. Each horse will have a different tolerance and can make recognizing the signs difficult. Below is a list of some of the more typical signs associated with gastric ulcers.

  • A change in attitude – Is your horse more nervous than usual or less willing to perform? Does he seem grouchy or “out of it” for no apparent reason?
  • Poor appetite – Is he eating as much as he normally does for the amount of work he’s accomplishing? Is he leaving any of his feed uneaten? Does he start to eat his grain, then back away?
  • Colic – Is your horse showing signs of low-grade colic, a persistent mild discomfort?
  • Decreased performance – Is your horse not as “fluid” as normal? Could his usually fine movement be described as below average?
  • Decline in body condition – Is your horse’s coat not quite as sleek and shiny as it once was? Does he look “unthrifty” or just plain poor?
  • Weight loss – Has your horse dropped weight, up to but not more than 10 percent of his body weight?
  • Dull – Is your horse generally lackluster and seemingly without energy?

Although the clinical signs of EGUS may be hard to recognize, diagnosis is quite simple. An endoscopic examination will reveal whether or not your horse has ulcers. The procedure is done under standing sedation on an outpatient basis. It is imperative that you follow your TEVA veterinarian’s recommendations and advice for fasting your horse prior to the procedure. If the stomach is full of food or water, there is no way to see whether or not there are ulcers. Some clinics prefer that you drop your horse off the night before so that they can ensure that he is properly fasted.

Ulcers are graded on a zero to three basis. Grade Zero means there are no signs of ulceration. Grade One means that there is a single to a few, small lesions present. Grade Two means multiple lesions up to medium sized are present. Grade Three means there are extensive, coalescing, deep ulcers, possibly bleeding, present.


Treatment is aimed at healing the ulcers and reducing the factors that cause them. Several medications are available that effectively treat gastric ulcers by reducing gastric acid secretion. FDA approved omeprazole products such as Gastrogard and Ulcergard have been proven to heal ulcers. Omeprazole is a proton-pump inhibitor that turns off acid secretion. Omeprazole products are given once daily and are, therefore, very convenient. Type-2 histamine (H2) blockers such as ranitidine have also been effective in treating ulcers. Histamine is a naturally-occurring chemical that stimulates cells in the stomach (parietal cells) to produce acid. H2-blockers inhibit the action of histamine on the cells, thus reducing the production of acid by the stomach.

Feeding calcium and protein rich alfalfa helps to buffer stomach acid. Reducing the amount of concentrate fed is also advised. Allowing as much access to pasture is also recommended.


Today we know the factors that induce gastric ulcers. Knowledge is power and we know that we can help to prevent our horses from actually developing a full blown case of ulceration. Veterinarians recommend treating horses prophylactically during stressful times such as trailering for lessons, competitions, or relocating, or when other horses in your horse’s circle of friends leave.

If a horse must be confined, ensure free choice access to hay and enrich the environment to reduce as much stress as possible. Provide toys (such as treat feeders), mirrors, and make sure he can interact or at least see his buddies.

Gastric ulcers can negatively affect your horse’s performance and health. Knowing what factors can cause them and signs to look for will help you identify if your horse is at risk or may even have ulcers.

Registered 2013 by Equestrian Collections
Author:  Sallie S. Hyman, VMD, DACVIM, CVA

Information in this article is for educational purposes only and is not a substitute for evaluation by an equine professional. In particular, all horse owners should seek advice and treatment from a licensed veterinarian, such as TEVA, for their horses' medical care.

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