Great Lakes Equine
Dr. Kate

Why do horses get ulcers, and what can we do to treat them? \ by Dr. Kate \

Unfortunately, ulcers are very common in horses. Multiple studies have shown between 25 to 51% of foals and 60 to 90% of adult horses have ulcers. So what causes all of these horses to have ulcers? It all comes down to an imbalance in the secretions of the stomach, with too many of the digestive factors like HCl (Hydrochloric acid), pepsin (an enzyme that breaks down proteins), and bile (a secretion from the liver that contains acids) and not enough of the protective factors like bicarbonate (an acid neutralizer in saliva) and mucus which protect the body’s cells lining the stomach from being digested with the feed. Unlike the human stomach, which secretes acid and other digestive factors only when we eat or get hungry, a horse’s stomach continuously secretes gastric acid and digestive factors since horses are meant to eat grass out on a pasture all day long. In fact, horses don’t even have a gall balder to store the bile the liver makes between meals; the bile just gets secreted as it gets made.   When a horse is kept on pasture and has a small intake of feed throughout the day, the constant intake of food absorbs the gastric secretions and prevents prolonged contact of the acid with the stomach surface. Conversely when horses are stabled and feed twice a day, their stomach is not able to control the secretions of acids and digestive enzymes to only when the horse is eating and the acid can begin to eat away at the stomach wall causing ulcers. Additionally, eating a few big meals instead of multiple small meals also decreases the amount of saliva that is produced and therefore the amount of bicarbonate that passes to the stomach to neutralize the acid.

There are several environmental factors and medications that can increase the chance of a horse getting ulcers. Any kind of stress in the horse results in a release of corticosteroids which can cause decreased blood flow to the cells that line the stomach wall, this in turn decreases the cells’ capacity to prevent the effects of being overexposed to stomach acid. There are a number of situations or events that can be stressful to horses and lead to ulcer formation such as a change in environment or intense training. Intense exercise can delay gastric emptying, so the food stays in the stomach for longer, allowing accumulation of more stomach acid and digestive factors. In one study 81% of racehorses in California had gastric ulcers compared to only 36% of horses not in any training. Also any horse that has another concurrent illness can be predisposed to ulcers due stress on the horse’s body or inconsistent eating. The same study showed that incidence of ulcers increased to 88% when the horse had another unrelated clinical problem. Some feeds may also predispose or protect horses from ulcers. Some by- products of digested feed, especially grain, may act synergistically with the digestive acids of the stomach to cause ulcers, while alfalfa, with its high protein and calcium content, may have more of a protective effect.

How are ulcers diagnosed in horses? Diagnosis of ulcers usually starts by observing the horse for certain clinical signs, although many horses often mask their pain so even a horse that is not showing clinical signs may still have ulcers.   Many horses with severe ulcers may exhibit signs of abdominal pain in the form of recurring colic or have gastric reflux. Others may have a poor appetite particularly for grain, or exhibit teeth grinding or excessive salivation. However, in many horses the signs may be more subtle and only show up as a change in attitude, mild dullness, or a decrease in performance.   Also in some studies ulcerated horses ate faster when their meal was late than non-ulcerated horses. Observation of any of these behaviors may create a suspicion of ulcers; however, the only way to get a definitive diagnosis is to do an endoscopic exam of the horse’s stomach. The horse would need to be fasted for 8-12 hours prior to the exam to empty the stomach and allow for maximum visibility. During an endoscopic exam a long flexible fibro- optic video endoscope is passed through the horse’s nose into the back of the throat and then down the esophagus into the stomach where the stomach can then be seen on a monitor.

Once gastric ulcers have diagnosed, how can they be treated? Feed supplements with active ingredients such as aluminum phosphates or calcium carbonate have been shown by researchers in Kentucky to only raise the stomach Ph for 2 hours and therefore do not allow enough time for ulcers to heal. Currently the only oral medication shown to be effective in treating existing gastric ulcers in horses is omeprazole. Omeprazole is the active compound in Gastrogard, which is presently the only FDA approved product for the treatment of ulcers in horses. So what is Omeprazole? It acts by blocking the secretion of H+ (Gastric Acid) by the cells that line the stomach. Unfortunately, it is not able to act locally right at the level of the stomach and must first be absorbed by the body into the blood before it can then act on the cells that line the stomach. Gastrogard is formulated with a carrier molecule designed specifically for horses so the drug it is able to survive the first pass through the stomach in order to be more effective. Although cheaper, the generic omeprazole products do not have this carrier and are therefore much less effective at treating ulcers. It may last as long as 27 hours in the horse depending on the dose given and was shown to allow healing in 77% of horses in race training with ulcers. Depending on the severity and location of ulcers on endoscopic exam a 2-6 week course of treatment may be recommended. We try and discourage skipping the endoscope going right for treatment as treatment is not inexpensive and the course of treatment varies greatly based on each case.

How are ulcers prevented in horses? One way is to provide turnout with grazing where it is available. Another option is to provide a hay net or another way to slow down the intake of food. The stomach pH falls about 6 hours after feeding so a horse should never go more than 6 hours without feed. Also consider a preventative dose of Gastrogard for the prevention of ulcers in horses in high stress situations.


Severe ulceration with active bleeding (at star) of the pyloric region of the stomach.

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