Acid test: Scientists review what we know about stomach ulcers in horses

Scientists who reviewed dozens of research papers dealing with stomach ulcers in horses have laid out key management strategies they believe can benefit affected animals.

Equine gastric ulcer syndrome is common, yet important elements around the troublesome condition are not yet fully understood. Its prevalence has been estimated at 25 to 50 percent in foals and 60 to 90 percent in adult horses, depending on age, performance, and evaluated populations.

The horse stomach has two distinct regions. The upper third is lined by the esophageal tissue (squamous mucosa). It has no glands to produce hydrochloric acid or mucus. The lower two-thirds of the stomach contain glands that secrete, among other things, hydrochloric acid and mucus, the latter designed to protect the stomach wall. Horses are continuous acid secretors. Acid production occurs regardless of whether feed is present.

The review team, Frank Andrews, Connie Larson and Pat Harris, writing in the journal Equine Veterinary Education, said ulcers in the lower part of the esophagus and upper non-glandular region of the stomach were probably caused by hydrochloric acid, because this region lacks protective mucus secretion.

Ulcers in the lower acid-producing glandular part of the stomach, and the upper duodenum, were likely caused by a breakdown in the mucus-based defense mechanisms.

Regardless of location, initial drug treatment was necessary to suppress acid production, they said. “However, nutrition and management changes are required to maintain ulcer healing and help prevent recurrence.”

The trio said that while nutritional factors were clearly involved in development of ulcers in the upper stomach, the role of nutrition in ulcers in the lower part of the stomach had yet to be defined.

Current evidence supported feeding a diet high in forage and low in non-structural carbohydrates (sugars), and feed being provided throughout the day and night to reduce the risk of ulcers in the upper stomach, they said.

In contrast, the role of diet in managing ulcers in the lower glandular stomach remained largely unknown.

However, they recommended the same feeding and management principles regardless of the location of the gastric ulcers.

Horses in general, they said, should be fed as much fibre/forage as possible. “Many horses and ponies do not require additional cereal-based feed but rather just an appropriate vitamin/mineral/protein forage balancer.” Prolonged periods without forage, leading to an empty stomach, should be avoided.

Andrews and his colleagues said horses in light or no work, or those considered “good doers”, may benefit from being fed lower-energy fibre sources so that time spent chewing was maximised. The use of double hay nets was one possible strategy.

Straw should be avoided as the only or main forage source, other than for donkeys, as evidence had shown it increased the gastric ulcer risk.

Ideally, horses should be fed less than 1 gram per kilogram of bodyweight of non-structrual carbohydrate meal per hay. If more is required, it should preferably be less than 2 grams per kilogram of bodyweight per day.

Owners should consider adding some chaff, which includes some alfalfa (lucerne), into the meal. Alfalfa hay has been shown to buffer stomach contents and lower the risk of gastric ulcers.

Should horses require extra energy, owners could consider gradually introducing supplemental vegetable oil, but only up to 1 ml per kilogram of bodyweight. The review team advised owners to check the vitamin and mineral balance of the resultant diet or choose a commercial, balanced high-oil, high-fibre feed.

Pasture turnout should be provided whenever possible, although they stressed that ulcers can be found in pasture-managed horses, especially if exercised intensively or supplemented with a high starch/sugar feed.

Good quality clean water should be provided continuously when on pasture. Water containers should be cleaned frequently to prevent overgrowth of algae and bacteria.

Stressful situations should be avoided for horses predisposed to ulcers, such as travelling long distances, a changing environment, and long periods of confinement.

Forage should be provided to horses during transport and immediately on arrival.

The review team said if stomach ulcers were diagnosed then medical management and appropriate pharmacologic treatment should be pursued, especially in the early stages of ulcers, and in particular for horses with severe ulceration and those who failed to respond to management changes.

Should horses need nonsteroidal anti-inflammatory drugs such as phenylbutazone or flunixin meglumine, a therapeutic dose should be limited to one and not “stacked”. While on these drugs, anti-ulcer drugs should also be given.

The reviewers said the key risk factors were exercise intensity, stall confinement, and feeding practices. The size and composition of non-forage meal had a profound effect on the risk of developing ulcers in the upper part of the stomach. Non-forage meals should be divided into smaller portions and fed 3 to 4 times daily.

Clinical signs commonly associated with gastric ulcers were numerous but often vague. Minor lesions were unlikely to cause any clinical signs. Clinical signs in worse cases can include poor performance, poor hair coat, picky eating and colic.

They noted that a 2011 study involving endurance horses indicated that work reduction alone was not enough to prevent the disease.

“Theoretically, removal of the horse from the risk factors that caused the condition in the first place and re-establishment of a normal pH gradient in the stomach should result in healing.

“However, anecdotally it appears that even when removal from the risk factors is possible, acid suppression therapy is often required to restore a normal appetite so that enough roughage is consumed to re-establish the stomach pH gradient. A normal pH gradient in the stomach provides a permissive environment to allow healing, especially in horses with weight loss and/or decreased appetite.

“Furthermore, the ability to remove risk factors, such as exercise and concentrate diets is often limited, so the use of acid suppression therapy remains a cornerstone in the management of non-glandular squamous ulcers.”

Therefore, once ulcers were observed, drug therapy – omeprazole or other effective agents – should be used, especially while horses remained in athletic training.

The authors noted that many equine dietary supplements or feed additives were available on the market for gastric ulcers.

“Many of these products have not been tested in horses, and this is a controversial area for many reasons, not least that in many parts of the world legislation restricts the claims that can be made for such products, which perhaps reduces the likelihood of studies being undertaken to support efficacy.”

However, even if a product was shown to work under precise experimental conditions, there was no way to know if it worked under real field conditions, where multiple risk factors may be present.

“Alternatively, if it does not work under experimental conditions, it may or may not work under field conditions or in an individual horse.”

The trio urged caution over the use of concentrated electrolyte pastes or solutions. Repeated oral use in endurance horses had been shown in one study to worsen squamous ulcers.

“At the moment it is recommended that such products should be used with caution in horses and that they may be best given after exercise, in hydrated animals and mixed in feed to minimise their effects on the squamous mucosa.”

Andrews is a professor and director of the Equine Health Studies Program within the Department of Veterinary Clinical Sciences at Louisiana State University. His areas of expertise include gastric ulcer disease; Larson is a research nutritionist with Zinpro Corporation in Minnesota; and Harris is a recognized veterinary specialist in equine clinical nutrition with the Waltham Centre for Pet Nutrition in Leicestershire, England.

Andrews, F. M., Larson, C. and Harris, P. (2017), Nutritional management of gastric ulceration. Equine Vet Educ, 29: 45–55. doi:10.1111/eve.12495
The abstract can be read here.