By Gary P. Carlson, BS, DVM, PhD

The objectives of this article are to discuss what we know about gastric ulcers in horses and how that information might relate to endurance horses and our sport. A quick Google search of the internet using the words “horse gastric ulcer” yields tens of thousands of hits. While there is a lot of information out there, not all of it is useful and some of it may be incorrect or misleading. There is very little published information on gastric ulcers in endurance horses.

We all know that some people develop stomach (gastric) ulcers. A variety of factors — from stress, to diet, to certain bacterial agents, to exposure to specific medications, to a person’s individual susceptibility — may contribute to the development of gastric ulcers. Gastric ulcers tend to develop when there is an imbalance between the normal protective factors of the stomach and various ulcer-promoting factors.

One of the key ulcer-promoting factors is the acidity of the stomach contents. Gastric ulcers have been found with some frequency in foals and in mature athletic horses. In otherwise healthy athletic horses, the presence of gastric ulcers does not always lead to the development of recognizable clinical signs. Serious blood loss or perforation of the stomach rarely if ever occurs.

There are significant anatomical differences between the stomach of the horse and humans. In many ways the gastric ulcers of athletic horses are more like the gastric acid reflux problems of humans. The bacteria, Helicobacter pylori, which plays a major role in certain common forms of gastric and duodenal ulcers in humans, has not yet been found to play a similar role in the horse.

Q: How do you diagnose gastric ulcers in horses?

A: The clinical signs of gastric ulceration in the horse are often vague and nonspecific. Signs thought to be associated with gastric ulceration include poor appetite or being a picky eater, rough hair coat, weight loss, diminished athletic performance or intermittent colic. However, most athletic horses with gastric ulcers show no obvious clinical signs. At present the only way to positively establish whether a horse has ulcers or does not have ulcers is the direct visualization of the stomach with a specialized piece of equipment, an endoscope or videoendoscope.

The endoscopes are delicate and expensive instruments similar to those used by physicians to examine the colon in humans. Instruments designed for use in horses generally exceed nine feet in length. They are often connected to sophisticated digital image recording devices.

To get a clear view, the stomach must be nearly empty of food and liquid contents. Most examinations are performed after an overnight fast, under moderate sedation, with a twitch in place. The endoscope is passed through the nostril and down the esophagus to the stomach, much like a common stomach tube. When ulcers are present, they are most commonly found in upper (non-glandular) portions of the stomach at the margin between the upper and the lower (glandular) portions of the stomach.

Q: What are the causes of gastric ulcers in horses?

A: This is a critically important question. The truth is, we do not fully understand the mechanisms by which various causal factors lead to the development of gastric ulcers in athletic horses. A likely key factor contributing to gastric ulceration in horses appears to be the exposure of the upper portion of the stomach to excessively acid stomach contents. The upper non-glandular portion lacks the protection of the complex mucous layer found on the surface of the lower glandular portion of the stomach and is thus more sensitive to the corrosive effects of a strongly acid environment.

Clinically normal horses at pasture have a very low incidence of gastric ulcers. In several research studies, the gastric ulcers observed by endoscopic examination resolved after the horses had been turned out to pasture. Horses at pasture eat nearly continuously. The stomach is seldom completely empty, and the acid fluid contents of the stomach may not have much direct contact with the acid-sensitive upper non-glandular portion of the stomach. The constant feed intake and the associated saliva swallowed, as well as the continued throughput of contents from the stomach to the small intestine, also reduce the accumulation of acid in the stomach.

During fasting, the acidity of the stomach contents increase dramatically. In one study, simply alternating 24 hours of fasting with 24 hours of feeding for a period of 96 hours resulted in the development of gastric ulcers in essentially all of the experimental horses. In other studies simply putting horses in stalls for a period of time was found to result in the development of gastric ulcers in most of the experimental horses. It is thought that change in the normal eating pattern of these horses during stall confinement was the important feature in ulcer development.

Horses in training for, and competing in, a wide range of athletic endeavors have been shown to develop gastric ulcers. The incidence and severity of gastric ulceration seems to be associated with the intensity of the exercise. Stress, transport, medications and a variety of management or feeding practices may contribute to ulcer formation. The one common feature thought to play a major role in ulcer formation in these equine athletes is the sloshing of the acid contents onto the non-glandular portion of the stomach during exercise.

Q: What is the incidence of gastric ulcers in horses competing in athletic events?

A: A number of studies have shown a high incidence (60%-90%) of gastric ulceration in Thoroughbred racehorses in training. Similar incidences are reported for Standardbreds and Quarterhorses in race training. One careful experimental study attempted to duplicate the experience of racehorses in training with regard to feeding, time spent in the stall and exercise, especially fast workouts but not actual racing. Within two weeks, all of the experimental horses developed gastric ulceration. Gastric ulcers have been found in competition and show horses with an incidence of less than 60% reported.

The incidence of gastric ulceration in endurance horses has received very limited study. There is only one published report of horses examined after an endurance ride of 30 or 50 miles. Of the 30 horses examined, more than 60% were found to have gastric ulcerations. The gastric lesions were slight and localized in most cases. Only two of the horses had moderate to severe ulceration. None of the horses showed clinical signs related to the presence of ulcers. These endurance horses had few of the management risk factors (high grain diet, pre-race fasting, stall confinement) thought to contribute to the high incidence of gastric ulcers in racing horses. Interestingly, a number of these endurance horses had evidence of some bleeding, but not discrete ulcers, in the glandular portion of the stomach.

Gastrointestinal problems are not uncommon in human endurance athletes. Gastrointestinal bleeding has been noted in some runners following marathon races, but the cause of this bleeding is not completely understood. Major blood loss into the bowel does not appear to be a common problem in endurance horses.

Q: Do certain medications contribute to the development of gastric ulceration?

A: Numerous studies have show that many of the anti-inflammatory drugs commonly used in horses may, in the right circumstances, be associated the development of ulcers in the stomach and other segments of the digestive tract. If these drugs are administered at excessively high doses, or if administered to dehydrated horses with compromised kidney function, toxicity may develop. Toxicity produces widespread damage to the gastrointestinal tract, kidneys and other organs. For these reasons care should be taken when these drugs are administered.

Having said all of this, in the few studies that have attempted to address this issue, there has not been a clear association between the use of these anti-inflammatory drugs and the development of the typical gastric ulcers observed in athletic horses. The gastric ulcers associated with the administration of anti-inflammatory drugs are primarily in the glandular portion of the stomach, whereas the ulcers observed in athletic horses are largely confined to the non-glandular portions of the stomach.

Endurance horses travel over long distances, often in hot and/or humid environments. Dehydration and electrolyte depletion are thought to play a role in limiting athletic performance and in the development of metabolic problems in some horses. With these thoughts in mind, a wide variety of mineral and electrolyte supplements are widely used to offset these deficits. Most riders feel these supplements given before and during endurance rides have been beneficial. However, if a horse fails to drink adequately, the administration of large amounts of highly concentrated supplements could be irritating to the stomach.

Q: How big a deal are these gastric ulcers in endurance horses?

A: Gastric ulceration in endurance horses is most surely not a new problem. We only became fully aware of the incidence of gastric ulceration in racehorses when endoscopes of sufficient length became available that allowed us to visualize the stomach. The gastric ulcers reported thus far in endurance horses seem to be less severe than those observed in racehorses.

Although some clinical problems have been shown statistically to be associated with the presence of gastric ulcers in racing horses, many and perhaps most athletic horses with ulcers show no obvious clinical signs and perform up to expectation. The author knows of no instances in which horses have died as a result of a perforated gastric ulcer during an endurance ride.

If you suspect gastric ulcers . . .

If you suspect your horse might have gastric ulceration, a complete veterinary examination is in order. There may be other lameness or medical issues responsible for the clinical signs or reduced athletic performance. If no other cause is found for these problems, you may wish to discuss with your veterinarian the option of having an endoscopic examination of your horse’s stomach. These are expensive and specialized pieces of equipment and not all veterinary practices will have them, but they are often available in regional referral centers. Endoscopic examination of the stomach is a moderately expensive procedure, perhaps several hundred dollars. However, treatment can be quite expensive and it makes sense to be sure that ulcer medications are clearly indicated.

Treatment and prevention

The management and treatment of gastric ulcers in horses should be decided by discussion between the owner and their veterinarian. Management and feeding practices may be the first things to consider. Horses showing clear clinical signs and widespread or severe ulcers may require a period of rest or turnout. The treatment of gastric ulcers in horses is largely directed at decreasing the acid environment in the stomach.

A wide variety of medications have been recommended for this purpose. They vary in price, effectiveness and ease of administration. Treatment options should consider the nature and extent of the horse’s problem, the planned ride schedule, as well as the cost and effectiveness of the medications used.

One of the most useful medications for the treatment of gastric ulcers in horses is the drug omeprazole. This drug is sold as a prescription treatment formulation under the brand name Gastrogard and as a non-prescription preventative formulation Ulcergard. This drug can now be given up to 24 hours before the start of an AERC sanctioned endurance ride.

Recurrences of gastric ulcers in horses in race training are common. We do not know if this is also true of horses in endurance training, although one would expect that it is. Once the ulcers have initially healed, a preventative program may be worth considering. Attention to management and feeding practices to avoid stress, turning out to pasture or feeding multiple times a day to avoid an empty stomach may be important. Some horses may require medications as well. Endurance horses have athletic careers that span many years, and we do not now know the long-term effects of various medications or the effects of prolonged suppression of the normal acidity of the stomach over this extended time frame.


How big a deal are these gastric ulcers in endurance horses? At present, we don’t really know for sure. Assuming that endurance horses have probably always had some gastric ulcers, and that many of these horses have had long and successful careers with no overt problems and no anti-ulcer medication, one approach would be to simply ignore it altogether. The opposite approach would be to assume the worst and treat every endurance horse as if he had severe gastric ulcers or was likely to develop them. Neither of these approaches seems very sound nor in the best interest of the horse or our sport.

The author is old enough to recall when the first flexible endoscopes were available for the examination of the upper airway of horses. It was soon discovered that nearly all young horses in race training had inflammation of the upper airway (pharyngitis). Various treatment regimes were soon devised; in time, it was found that the changes seen were part of the normal response of young horses to the typical respiratory agents encountered in the racing environment.

As another example, gastric ulceration can be a serious problem in ill or debilitated neonatal foals. At one time it was recommended that all seriously ill neonatal foals be treated with anti-ulcer medications on the assumption that they all had ulcers or they would soon get them. Now, in many neonatal intensive care facilities, anti-ulcer medications are used much more selectively when there is a clear indication.

These experiences may or may not apply to the present discussion, but they lend a sense of perspective when attempting to deal rationally with a newly recognized problem. What is needed at this time is more information and specific research on gastric ulceration in endurance horses. In the end, a combination of sound research data, practical experience and common sense will lead to balanced understanding of the problem and how to best reduce its impact on our equine endurance athletes.

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