We will be continuing our series of articles on colic by discussing causes of colic that originate in the stomach.


Gastric ulcers are a relatively common condition in the horse. This is especially true of racehorses and high level show horses, but they can affect any horse. Gastric ulcers are a complex problem, so we will just discuss the basics in this article.

The mucosa is the tissue layer that lines the inside of the stomach. In the horse there are two main types of mucosa. The glandular mucosa and the non-glandular or squamous mucosa.

The glandular mucosa is located in the lower portion of the stomach and contains parietal cells, which secrete hydrochloric acid to make the stomachacidic, and zygomatic cells, which secrete pepsinogen, an enzyme that breaks down protein. The glandular mucosa has multiple protective mechanisms, which prevent it from becoming damaged by the acidic gastric fluid. These mechanisms include mucous and bicarbonate secretion1. The non-glandular or squamous mucosa is located at the top of the stomach and rarely comes into contact with the very acidic gastric fluid. As a result it has fewer protective mechanisms against the acidic gastric fluid. Most gastric ulcers occur in the non-glandular or squamous part of the stomach.

A gastric ulcer occurs when a portion of the mucosa is damaged. This exposes the much more sensitive internal tissue to the acidic gastric fluid resulting in discomfort or pain. The more layers of mucosa that are lost, the deeper and more significant the ulcer. Adult horses with gastric ulcers can have a wide variety of clinical signs. The signs include mild colic signs, especially after eating, decreased appetite, and poor performance. Younger horses may have more significant colic signs. Because the clinical signs can be so varied and non-specific, gastric ulcers can only be definitively diagnosed with a gastroscopy, where a small camera is passed down the esophagus and enables direct visualization of the inner lining of the stomach. This procedure is performed in the standing horse with light sedation.

There are multiple risk factors for the development of gastric ulcers. Fasting has been shown to alter the pH in the stomach and increase the risk for ulcer development. Fasting during the day has been shown to be more detrimental than fasting overnight when there is a natural increase of the horse’s stomach pH. Thus constant access to feed, especially during the day, can decrease the risk2. Ulcers are very common in racehorses and other intensely managed groups of horses suggesting that stress plays a role. High starch diets have also been shown to be associated with an increased risk of developing gastric ulcers3 . The use of medications such as phenylbutazone (bute) or banamine can impair the ability of the gastric mucosa to protect itself from acid and can cause ulcers.

If gastric ulcers are visualized on gastroscopy, they are treated with omeprazole (trade name Gastroguard or Ulcerguard). Omeprazole decreases the acid production in the stomach thereby increasing the pH of the gastric contents (makes it less acidic). Scientific studies have shown that generic forms of omeprazole are often not effective in reducing the pH in the equine stomach, therefore the name brand Gastroguard or Ulcerguard product is recommended4. Recent studies have also shown that Gastroguard is more effective if it is given when the horse has a relatively empty stomach. Thus dosing in the morning before breakfast is recommended. It is also very important to try and limit risk factors for gastric ulcers to prevent their reoccurrence after successful treatment. Modifications in diet, the use of slow feeders or multiple small feedings, increased turnout, and decreased stress can all help prevent the development or re-occurance of gastric ulcers.


Gastric impactions are another cause of colic related to the stomach. Gastric impactions involve accumulation of feed material or a foreign object in the stomach. The large volume of impacted feed in the stomach causes mild to severe colic and if untreated can lead to gastric rupture, which is a fatal condition. Horses can be diagnosed with a gastric impaction on gastroscopy (when the stomach is evaluated with a small camera), when large volumes of feed material are lavaged from the stomach during a colic exam, or at surgery. Treatment involves passing a nasogastric (nose to stomach) tube and instilling fluid to help break up the impaction. Occasionally a horse swallows a foreign object, which becomes lodged in the stomach or may block stomach outflow. Surgery may be needed to remove the foreign object.


Stomach masses or tumors are very uncommon, but can be an occasional cause of colic related to the stomach. The most common type of mass or tumor in the stomach is squamous cell carcinoma. At the time of diagnosis, these tumors are often too large to remove and unfortunately euthanasia may be indicated.


  1. Wilson, DA, Blikslager, AT: The Stomach and Spleen. P.388. In Auer JA, Stick JA (eds). 4th Ed. Elsevier, St. Louis, 2012.
  2. Husted, L, Sanchez, LC, Baptiste, KE, Olsen, SN. Effect of a feed/fast protocol on pH in the proximal equine stomach. Equine Vet J 2009 Sep; 41(7):658-62.
  3. Luthersson, N, Nielsen, KH, Parkin, TD. Risk factors associated with equine gastric ulceration syndrome (EGUS) in 201 horses in Denmark. Equine Vet J 2009 Sep;41(7):625-30.
  4. Merritt, AM, Sanchez, LC, Church, M, Ludzia, S. Effect of GastroGuard and three compounded oral omeprazole preparations on 24 h intragastric pH in gastrically cannulated mature horses.