Causes, Prevention and Treatment

By Margaret Evans

Gastric ulcers in horses are far more common than many people realize. The condition is very often found in horses kept in stalls, frequently trailered, or undergoing intensive training. The associated anxiety, in addition to artificial and controlled feeding routines alien to a horse’s natural grazing patterns, may put the animal under varying levels of stress.

According to Prof. Jorge Nieto with Surgical and Radiological Sciences, University of California, Davis, gastric ulcers can affect any horse at any age. In adult horses, gastric ulcers occur more frequently in animals that perform athletic activities with the highest frequency found in Thoroughbred racehorses (80 to 90 percent), followed by endurance horses (70 percent), and show horses (60 percent).

The stress of trailering, competing, and adjusting to strange surroundings can contribute to the horse’s risk of developing an ulcer. Photo: ©Shutterstock/Pirita

Researchers have found that exercise increases gastric acid production and decreases blood flow to the gastrointestinal (GI) tract. During exercise, the fluid in the lower segment of the stomach, where gastric acid is secreted, splashes and exposes the more vulnerable upper segment of the stomach to an acidic pH.

With an increase in exercise, training, and a demanding competition schedule, riders may sometimes change feeding routines, perhaps switching to more fasting and offering less roughage. That can put a horse on a path to developing an ulcer. In addition, the stress of trailering, competing, and adjusting to strange surroundings can add to the risk of ulcer development.

But to better understand gastric ulcers it is first necessary to understand the workings of the horse’s stomach. 

A horse has a small stomach compared to its size and, in fact, compared to the size of stomachs of a number of other species. It holds only about four gallons of food. This is because horses evolved to graze and move constantly. As prey animals, their flight instinct means they are always be ready to move to safer ground in the face of danger. It has served them well to be able to thrive on small, snack-like meals processed by a small stomach that, under optimum conditions, was seldom empty.

Up to 90 percent of Thoroughbred racehorses have gastric ulcers. Photo: ©Canstockphoto/Shariffc

Those eating habits did not disappear with domestication. The need for frequent small meals is just as important today in a controlled stall or paddock environment as it was when they were wild. In fact, horses in the wild today do not get ulcers. Unfortunately, it is the diet and lifestyle we have placed on horses that has brought about this painful and disabling condition. The good news, though, is that gastric ulcers are both curable and preventable with adjustments in feed, a feeding routine that matches their physiological needs, and measures to reduce the horse’s stress and anxiety.

“The horse’s stomach is divided into two distinct regions: the squamous region at the top (considered a continuation of the esophagus lining) and the glandular mucosa at the bottom (similar to the human stomach),” says Nieto in The Horse Report published by the Center for Equine Health, School of Veterinary Medicine, University of California, Davis. “The bottom part is glandular and secretes gastric acid. However, this region also produces mucus and bicarbonate which protect the mucosa from acid exposure. So even though this region is also exposed to acid for several hours a day, it is not a common place for ulcer formation. When ulcers do form in this region of the stomach, they are usually secondary to chronic administration of nonsteroidal anti-inflammatory drugs (NSAIDs). 

The equine stomach consists of two distinct regions, the non-glandular, squamous region and the glandular region, divided by a stepped ridge, the margo plicatus.

“The top portion of the stomach is designed for mixing of the contents of the stomach and does not have as much protection from the acid. This is the most common place to find gastric ulcers. The lining of this section of the stomach is very thin and does not have many mechanisms for acid protection. Because the horse’s stomach produces gastric acid at all times, even when not eating, the squamous mucosa is exposed to acid several hours a day, which can easily erode the lining of this region.”

Gastric acid, also called hydrochloric acid, together with an enzyme called pepsin are needed for the digestion of food. Humans too need hydrochloric acid for digestion, but it is produced when we eat. Horses, however, produce the acid all the time and, on an empty stomach, it can start to irritate the non-glandular section of the stomach.

NSAIDs such as phenylbutazine (Bute) or flunixin meglumine (Banamine®) stop inflammation and pain by inhibiting prostaglandins, which decrease blood flow to the stomach lining. This will in turn decrease the production of the mucus layer in the stomach and remove its protective layer, making it more susceptible to the onset of ulcers. Not every horse reacts to nonsteroidal medications, but the potential for side effects should be considered when medications are being recommended. 

Because of the horse’s need to eat small, frequent meals, his stomach is producing digestive acid constantly. Nieto says that the stomach can produce up to nine gallons of acidic fluid a day. This fluid is buffered by a high roughage diet and the horse’s own saliva which, when swallowed, helps to neutralize the stomach acid.

The problem with constant stall confinement is that a feeding schedule in which considerable time gaps occur between feedings can hamper a horse’s overall health. In addition, if grain concentrates are given, they can produce fatty acids that may also contribute to the onset of ulcers.

Turnout has huge benefits for not only the health of the horse’s stomach, but also for his mindset. Pasture turnout allows some form of grazing even during seasons when the grass isn’t growing. It also provides opportunities to move, roll, blow off steam, and socialize with others even if it’s just an over-the-fence conversation. Horses are highly social animals and crave the company of their own kind. With some freedom to move naturally, anxiety, stress, and boredom are reduced.  

Knowing if your horse has a gastric ulcer means watching for signs that might be subtle at first. These include weight loss, poor coat, poor appetite, a dullness and shift in attitude, sluggish performance, a tendency to lie down more often, low grade colic, or loose feces. Some horses will lie on their backs, a position that foals will often adopt, as it seems to relieve the stomach irritation.

Foals will show signs of intermittent colic, interrupted nursing, diarrhea, poor or distracted appetite, teeth grinding, and excessive salivation. Nieto says that foals are especially susceptible because they secrete gastric acid as early as two days of age and the acidity level is high. Foals that have infrequent or interrupted feeding, or are recumbent for long periods, have been found to have lower gastric fluid pH suggesting that the dam’s milk has a protective effect against ulcers.

Above: Healthy epithelium in the non-glandular and glandular gastric regions. Below: Gastric ulcers in the non-glandular gastric region.

Photos courtesy of Dr. Fernando J. Marqués

Veterinary intervention for any horse or foal showing signs of gastric ulcers is essential and an examination will include an inspection of the stomach lining with a gastric endoscopy. Once the horse is sedated, the tube with a light and camera on the end is inserted through the nostril and down the esophagus into the stomach where the vet is able to examine the lining, look for lesions, and then prescribe the best treatment for the condition. It’s a safe, quick examination that will lead to a more effective treatment and if necessary, more appropriate long-term feeding management.

Omeprazole, available as an oral paste from your veterinarian under the trade name Gastrogard®, has proven to be effective in treating gastric ulceration in horses of all types. It is also considered valuable for the prevention of gastric ulcers during periods of increased stress, which can be triggered by such things as trailering, stabling in new environment, or the demands of competition. Nieto stresses the importance of using the original product and not a cheaper derivative, which may not contain the effective proportion of omeprazole in its ingredients. 

Prevention being preferable than the need for a cure, some management changes can go a long way to providing a lifestyle that maintains the horse’s physical comfort level, leading to a greater willingness to perform in the ring. Decreasing exposure to stressful situations, such as avoiding unnecessary trailering and lowering the intensity of the horse’s exercise program, can reduce some of the risk, but a change in feeding routines and management may be the most important long range factor in prevention.

Daily pasture turnout for grazing and socialization is the absolute best choice. Even if horses cannot be turned out together, it is highly preferable that they can at least see each other. If the horse must be contained in a stall, small frequent feedings of roughage will increase saliva, control acid production, and help mitigate the threat of ulcers. If the horse tends to gobble his hay, using a slow feeder hay net with a smaller mesh size will be helpful to extend the feeding period.

The capacity of feeds and forages to play a role in ulcer prevention by counteracting changes in the gastric pH of the equine stomach is commonly known and accepted. In studies, alfalfa hay has been shown to be effective in providing superior buffering capacity compared to other forages, thereby reducing the severity of ulcers in horses.

The alfalfa plant (also known as lucerne) is one of the world’s oldest crop plants. It is a perennial flowering plant belonging to the pea family and has the highest nutritional value of all hay or forage crops. Rich in protein with high levels of calcium and fibre it contains every essential amino acid, a wide range of vitamins, minerals and trace elements as well as enzymes important for food digestion. 

For diet options to help prevent ulcers, reduce or avoid oats and other cereal grains, as starchy feeds can stimulate the production of more acid. Grains move through the stomach quickly leaving it empty and vulnerable. Instead, try feeding beet pulp – it’s an excellent source of digestible fibre with low crude protein. For horses having trouble chewing hay, soaked beet pulp makes an appetizing choice and it can be stirred in with a grain ration. Soaked timothy/alfalfa hay cubes work very well, too. If you add oils to the horse’s meal, use vegetable oils such as flax rather than soybean or corn oil, which have high omega 6 content and may cause inflammation.

The best advice for prevention through feeding is to have a thorough discussion with your veterinarian about your horse’s unique nutrition needs and his own sensitivities, how often he should be fed, and whether additional supplements should also be given.

Horses evolved over millions of years with a feeding routine and digestive system that supported survival. Rather than making artificial adjustments to fit our own lifestyle to the detriment of our horse’s health, allow your horse to live as naturally as possible by reducing anxiety and stress, providing daily turnout, and carefully managing his feeding program. 

Main Photo: Left to live naturally, horses will move and graze constantly. Their stomachs are seldom empty, they have less anxiety, and they do not get gastric ulcers. It is the diet and lifestyle we impose upon our horses that has brought about this painful condition. ©Canstockphoto/Alexia Khruscheva