Understanding gastric ulcers in horses

Abstract

It has been more than 20 years since gastric ulcers in horses were first described. Since then, a lot of research has been conducted to discover the cause, or causes, of these ulcers and to test various drugs for treatment of the condition. At first, it was assumed that ulcers in horses were rare occurrences. Subsequent studies revealed that gastric ulcers are very common in racehorses and can cause loss of peak performance. Studies have shown that about 90% of all horses in strenuous training and racing have gastric ulcers. Gastric ulcers in horses are not entirely unlike ulcers in humans. Drugs developed for humans were tested and found to be effective in horses. It has generally been thought that stress causes ulcers in humans, and so it is natural to consider stress as the probable cause of ulcers in horses. Another possible cause of gastric ulcers is infection with the bacteria Helicobacter species. Research is underway in horses to determine what role these bacteria might play in the development of ulcers in horses. The use of a long endoscope makes it possible to observe ulcers in the live horse, and many equine practitioners use these endoscopes on a routine basis today. This technique has made it possible to determine the incidence of ulcers in various groups of horses. It has been found that usually the ulcers occur in the upper nonglandular portion of the stomach, the squamous-lined proximal region, which is not normally exposed to the acids that sit in the bottom of the stomach. The latest theories about causes of ulcers in horses relate to several types of ulcers, any one of which could result in equine gastric ulcer syndrome. An increased amount of stomach acid has been thought to be the underlying cause. It has been assumed by many that an increased production of stomach acid occurs, but in rare incidences there is a mechanical blockage of the outlet to the stomach, causing a backup of acid fluid. Research in both humans and horses is aimed at finding what causes increased acid production in the stomach. Until recently, the 2 major suspects are stress and the type of food eaten. Stress in racehorses can be extreme, and it is closely associated with the occurrence of ulcers. Young horses closely confined are also under a great amount of stress and they have a high incidence of ulcers. Everyone realizes that certain foods can cause a very uncomfortable feeling in the stomach. Often, this is because of acid buildup. Studies have been conducted to determine if the type of feed influences the development of ulcers in horses. One study suggested that horses fed alfalfa had fewer ulcers than those fed grass hay. More research is needed in this area, however, before equine-feeding regimens should be changed. Dr. A. M. Merritt, a well-known researcher in equine gastrointestinal problems, has studied the etiology of gastric ulcers in horses. He has concluded that exercise is a major cause. Recently, at the Medical Forum of the American College of Veterinary Internal Medicine, he explained why he believes exercise contributes to the development of gastric ulcers. He pointed out that exercise as a cause of ulcers in humans has been well documented. “We hypothesized that the increase in intra-abdominal pressure during exercise pushes gastric contents up into the squamous-lined proximal region of the stomach,” he said, “exposing that mucosa to corrosive agents, most notably acid, within those contents.” The horse’s stomach is not normally filled, and most horses, if left to their own devices, spend the majority of a day standing or walking around so this part of the stomach is not exposed to the contents, according to Dr. Merritt. “Horses in training,” he explained, “spend a significantly larger part of their day moving at faster gaits resulting in relatively prolonged exposure of the squamous epithelium to gastric contents.” Dr. Merritt believes that the high incidence of squamous (nonglandular) gastric mucosal ulcers in horses in training is primarily a mechanical phenomenon caused by an increased exposure of that region of the stomach to acidic gastric contents during exercise. He suggests administering one of the antiulcer drugs between 1 to 6 hours after exercise. Copyright 2002, Elsevier Science (USA). All rights reserved. 0737-0806/02/2207-0012$35.00/0 doi:10.1053/jevs.2002.36745