Gastric ulceration refers to defects in the mucosal (inner) lining of the stomach that extend into your horse's underlying muscular layer. In contrast, gastric erosions do not extend into the muscular layer. Ulceration occurs when there is an imbalance of digestive factors such as hydrochloric acid and protective factors such as mucus, protective prostaglandins and blood flow to the mucosal lining.
Studies show up to 70-90% of sport horses will have some degree of gastric ulceration when evaluated endoscopically. However it is important to note that not all of these horses will demonstrate signs consistent with gastric ulceration.
Few specific causes of gastric ulceration in horses have been clearly identified. There has been an association with stressors and ulceration in foals, intense training, and low volume roughage feeding. There has been no definitive link between bacterial infection with H. pylori and gastric ulceration as is the case with people. Horses, unlike people, are continuous secretors of gastric acid. This is in line with their natural lifestyle as continuous grazers. If there is not a constant volume of roughage in the stomach to buffer the continuously secreted acid, ulceration will develop. Administration of certain drugs such as phenylbutazone and banamine has been shown to induce gastric ulceration in horses. They do so by inhibiting the production of protective factors such as prostaglandin E2.
Anatomy of Your Horse's Stomach
Horses have small stomachs relative to their body size. The average horse's stomach can only hold approximately 4 gallons. This is in line with their eating habits in the wild - consuming frequent small meals, so their stomachs are never stretched to full capacity. The inner lining of your horse's stomach is made up of two parts separated by the margo plicatus. The primary difference between these two parts is the types of cells lining them: the squamous mucosal epithelium and the glandular mucosal epithelium.
The glandular epithelium contains many glands that produce gastric secretions. There, feed material is mixed with hydrochloric acid and pepsin to begin the digestive process. This glandular portion of the stomach also secretes a mucus-bicarbonate layer that helps protect its lining.
The squamous epithelium contains no glands, and merely serves to contain food, without aiding in any chemical digestion. However, the secretions that protect the glandular epithelium lining have no protective effect on the squamous epithelium lining, putting it at greater risk from increased acid production.
When should I suspect that my horse has ulcers?
Symptoms associated with gastric ulceration in adult horses may include recurrent or acute low-grade colic especially after eating. A decreased appetite for grain is also common. Greater amounts of acid are released when a horse eats grain. As a result, horses with gastric ulceration may learn to associate the consumption of grain with the pain associated with release of acid onto an ulcerated stomach. Decreased manure production, poor body condition, poor haircoat, poor performance and a change in the horse's normal attitude may also be seen.
How is a Diagnosis of Gastric Ulceration made?
The only way to definitively diagnose gastric ulceration is to have a gastroscopic examination performed. The exam is performed under sedation and takes approximately 15-20 minutes. Your horse will need to fast for 10-12 hours prior to the procedure. Gastroscopic examination in the hands of an experienced clinician will allow for a thorough evaluation of the entire stomach, including both the squamous non-glandular layer and glandular layers. The exit portal of the stomach, called the pylorus, should also be evaluated for any abnormalities of function or structure. Finally, the stomach should be exited, and the portion of small intestine, the duodenum, coming off the stomach evaluated for ulceration. Duodenal ulceration is seen most often in foals and weanlings.
Treatment of Gastric Ulceration
Treatment of gastric ulceration generally involves the use of medications that suppress gastric acid production. Gastrogard® or Ulcergard® are proton pump inhibitors, while drugs such as ranitidine (Zantac®) and cimetidine (Tagamet®) are histamine receptor antagonists. Both classes of drug work well to treat existing ulcers. Choice often comes down to practicality, as Gastrogard is administered once daily while ranitidine and cimetidine require three times a day administration. A 30-day course of treatment with either class of drug is recommended.
Sucralfate (Carafate) is a different class of drug used in the treatment of gastric ulceration. It is most effective in treating ulcers of the glandular mucosa. Sucralfate acts locally in an acidic environment (pH < 4), reacting with stomach acid to form a thick paste-like material capable of acting as an acid buffer as long as 6 to 8 hours. It also attaches to proteins on the surface of ulcers to form complexes that serve as protective barriers at the ulcer surface, preventing further damage from acids and bile. It has been shown that sucralfate also stimulates the increase of gastroprotective factors such as prostaglandin E2, epidermal growth factors (EGF), and gastric mucus. A 30 day course of treatment with sucralfate is also recommended for glandular ulcers.
A repeat gastroscopic exam should be performed towards the end of the treatment to determine if the ulcers have fully healed or whether treatment should be continued. Some horses may need to be maintained on preventative ulcer therapy once the active ulcers are fully healed.
Prevention of Gastric Ulceration
Administration of either proton pump inhibitors or histamine receptor antagonists can be used for the prevention of ulceration, once any ulceration has been effectively treated. Diets rich in calcium such as alfalfa hay have been shown to be effective in the prevention of gastric ulceration. Environmental management is also critical. Frequent small meals, free access to unlimited amounts of roughage, and ample turn-out time are also critical to the well-being of the horse's stomach.