Written by Kaitlyn Garman and Ian Hauffe under the direction and review of Russ Daly and Cody Wright.

Gastric ulcers are sores that occur inside the stomach when its lining has become damaged. Horses are subject to ulcers due to their compound stomach. These ulcers can become life-threatening if not managed or treated. While short-term interventions for gastric ulcers such as medication are available, managing the horse’s diet, along with other management strategies, is key to reducing the long-term risk of ulcers.


Horses of various ages and breeds are susceptible to equine gastric ulcer syndrome. Horses commonly experience two different types of ulcers: squamous ulcers and glandular ulcers. Squamous ulcers are thought to be caused by exposure to stomach acids such as hydrochloric acid, lactic acids, and volatile fatty acids. These acids are secreted in response to various factors such as the size and nature of a meal along with the acidity or alkalinity of the stomach pH (intragastric pH). The horse’s intragastric pH can be affected by nutritional components such as alfalfa hay and grain which are higher in pH than brome grass hay which have a significantly lower pH. When a low-pH environment is exposed to acids, sodium transport is impaired in the stomach lining cells, which results in cell swelling and over time squamous ulcer formation. In contrast, glandular ulcers are thought to be caused by a breakdown in the normal stomach lining defense mechanisms, including mucus, bicarbonate, and blood supply.

Risk Factors

Horses that undergo strenuous or prolonged exercise, such as performance horses and race horses, are at a higher risk of developing both squamous ulcers and glandular ulcers. It’s believed this higher risk is due to the common practice of taking performance horses off feed before exercise. This results in a lower stomach volume, which in turn drops the stomach pH. Horses housed in stalls are also at higher risk of developing ulcers, as factors such as feeding practices and stress may contribute to ulcer formation. Horses allowed to graze in a pasture or eat as they please are at a lower risk of developing squamous ulcers. This is because grazing provides a continuous flow of saliva and ingesta that can buffer stomach acids. Nutritional risk factors associated with the development of squamous ulcers include the size and composition of starch in non-forage supplementation, as found in high starch-low forage diets. Forage type (alfalfa vs. brome grass hay) can also influence ulcer formation due to effects on stomach pH. Lastly, particle size is also associated with ulcer formation: feeding finely ground pellets increases the ulcer risk compared to feeding larger pellets.


Poor performance is one common sign of equine gastric ulcer syndrome. Other signs associated with ulcers include poor hair coat, picky eating, and colic. Nonetheless, some horses may not show signs associated with ulcers, and some signs may be obscure and easily missed. Presumptive diagnosis of equine gastric ulcer syndrome requires a physical examination and a positive response to antiulcer treatments, but a conclusive diagnosis requires a gastroscopic examination.


The most common management practice to reduce the severity and risk of gastric ulcers is pharmacological therapy, which increases stomach pH by suppressing hydrochloric acid. Reducing exercise intensity and increasing pasture turnout may help decrease ulcer development. In addition, dietary modifications such as feeding feeds with larger particle size, lower starch concentration, and reevaluating forage type should be considered. If acid suppression therapy and dietary modifications are not effective, antibiotic therapy may be considered.

Dietary Regimen

One dietary practice that may reduce ulcer formation is to feed a forage-based diet ad libitum. These diets should consist of alfalfa hay or quality grass hay in addition to the feeding of balanced rations. Additionally, stalled horses should be fed three or four smaller meals per day that include less grain and nonstructural carbohydrate feeds. Dietary supplements are also available for treatment of gastric ulcers, however, many of these products have not been tested on horses. Some examples include sea buckthorn berry extract as well as oils such as corn oil and rice bran oil.


Nutritional management and diet play a large role in the formation and maintenance of gastric ulcers. To reduce the risk of ulcers, horse owners should provide a diet that is high in forages and feed ad libitum. This can be achieved by implementing pasture turnout, increasing the amount of forage, and reducing the amount of grain. Medical management may be required for horses that do not respond to management and dietary modifications. Diet and nutritional management, however, are keys to reducing the risk and recurrence of this important aspect of a horse’s health.

Source: SDSU iGrow