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Gastric ulcers have been known to plague horses that are confined a majority of the time, travel often, compete in new surroundings, and face abrupt changes in diet. Simply put, gastric ulcers may result whenever a horse is placed in an unfamiliar or stressful situation for any length of time. Fortunately, there are ways to mitigate the effects and prevalence of gastric ulcers.

Performance horses are generally kept in confinement during training without access to grazing. This combined with large quantities of grain intake leads to a number of gastrointestinal problems such as gastric ulcers and colic. Many studies since the mid-1980s have documented that gastric ulcers are commonplace in racehorses. An early postmortem study in Hong Kong of 195 Thoroughbred racehorses showed that 80% of the horses in active training had ulcers. The incidence of ulcers in horses retired from racing for one month or longer was 52%. Other researchers examined the stomachs of 187 horses ranging in age from one to 24 years. Eighty-seven horses had clinical problems including recurrent colic, poor body condition, or chronic diarrhea. One hundred horses had no clinical signs of gastrointestinal problems. Ninety-two percent of the horses with clinical problems had gastric ulcers. Surprisingly, 52% of the horses displaying no clinical signs also had lesions. Racehorses in training had a higher incidence of ulcers (89%) than nonracers (59%).

Another study evaluated the incidence of gastric ulcers in California racehorses. In one postmortem study of 169 horses, 88% of Thoroughbred horses in training had ulcers. A gastroendoscopic study of 202 Thoroughbred horses in training showed that 81% had ulcers. Each of these studies produced remarkably similar results. Eighty to ninety percent of racehorses in training have gastric ulcers. Most of these lesions occur in the region of the stomach above the margo plicatus, with very few lesions in the glandular portion. The upper half of the stomach consists of squamous epithelial cells that are very similar to the tissue found in the esophagus. Ulcers in this part of the stomach are more similar to esophagitis (heartburn) in humans than the ulcers that occur in the glandular region of the human stomach. It has also been determined that equine gastric ulcers are not caused by Helicobactor pylori bacteria, which are a common cause of ulcers in humans.

The high incidence of ulcers observed in performance horses is a man-made problem resulting from the way that performance horses are often fed and managed, since ulcers are much less common in horses maintained solely on pasture. Horses evolved as wandering grazers with digestive tracts designed for continual consumption of forage. Meals of grain or extended periods of fasting lead to excess gastric acid output without adequate saliva production.

Horses secrete acid continually whether they are fed or not. The pH of gastric fluid in horses withheld from feed for several hours has consistently been measured to be 2.0 or less. Horses that received free-choice timothy hay for 24 hours had mean gastric pHs that were significantly higher than fasted horses (3.1 in fed versus 1.5 in fasted horses). Higher pHs in hay-fed horses should be expected since forage consumption stimulates saliva production. Researchers measured the amount of saliva produced when horses ate either hay, pasture, or a grain feed. When fed hay and fresh grass, the horse produced 400-480 grams of saliva per 100 g of dry matter consumed. When a grain-based feed was offered, the horses produced only about half (206 g/100 g dry matter) as much saliva.

Most horses in training are confined for most of the day and fed large grain meals. Often, racehorses are fasted for an extended period before exercise, allowing gastric acid to accumulate in the stomach. Intense exercise further increases the production of gastric acid so that the squamous mucosa of the stomach gets thoroughly bathed in acid during work.

Treating ulcers involves either inhibiting gastric acid secretion or neutralizing the acid produced. An alternative to suppression of acid production is to neutralize stomach acid and protect the squamous mucosa from exposure to acid. The natural buffering mechanism in the horse is from saliva production and indeed the most effective way to treat ulcers is simply to turn out the animal on pasture. In situations where this is not possible, administration of antacids may be a useful adjunct to acid suppression therapy in horses.

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