Recent studies have shown that up to 90 percent of racehorses and 60 percent of show horses are affected by gastric ulcers. Exposure of some portions of the stomach lining to normal stomach acids for prolonged periods of time causes erosion and ulceration of this surface. The digestive tract of the horse is designed for continuous grazing, thus acid secretion from the stomach is continuous. If the horse is not eating hay or grazing continuously, the acid is not neutralized and may predispose the stomach lining to ulceration. Although bacteria have been shown to cause ulcers in humans and dogs, this has not been proven in horses.
The horse’s stomach is divided into two parts. The bottom portion, lined by glandular mucosa, secretes acid and has protective mechanism to keep it from being damaged by acid. Ulcers are being seen more commonly in this area of the stomach, but the exact mechanism by which they occur is still unproven. The top portion, lined by squamous mucosa, is designed for mixing of the contents of the stomach and does not have as many protective barriers from the acid. As acid splashes onto the relatively unprotected squamous portion of the stomach, ulcers are created.
Risk Factors for the Development of Gastric Ulcers
- Stall confinement, without continuous access to hay, can lead to the development of ulcers. When horses are fed two times per day, the stomach is subjected to a prolonged period without feed to neutralize the acid.
- Diets that consist of a large amount of grain, such as sweet feeds, oats, etc., produce volatile fatty acids that can contribute to the development of ulcers.
Stress also predisposes to the development of gastric ulcers in horses. Shipping, confinement, mixing groups of horses and heavy training can lead to ulcers.
Strenuous exercise can contribute to ulceration by decreasing both the emptying function of the stomach and blood flow to the stomach.
- Chronic administration of non-steroidal anti-inflammatory drugs such as phenylbutazone (bute) and Banamine can decrease the production of the stomach’s protective mucus layer, making the stomach more susceptible to ulcers.
Many horses with gastric ulcers do not show outward symptoms, or the symptoms may be subtle. Although some horses may seem to show no outward signs, if ulcers are detected by gastroscopy (see below) and treated, an improvement in attitude and performance are often observed. More apparent but mild signs of gastric ulceration may include a poor appetite, increased recumbency (laying down), decreased performance and a dull hair coat. Some horses, however, show more severe signs such as colic (abdominal discomfort) and weight loss.
The only way to definitively diagnose gastric ulcers is by gastroscopy. This procedure involves placing an endoscope directly into the stomach. The endoscope is a long, thin tube with a light and a tiny camera on the end, which allows direct visualization of the stomach lining. To perform the procedure effectively, the stomach must be empty, so most horses are held off feed for 6 to 12 hours and not allowed to drink water for one to two hours prior to gastroscopy. With light sedation, the endoscope is passed through the nostril and down the esophagus into the stomach. The procedure is well tolerated by horses and usually takes less than half an hour to perform.
Gastroscopy is important for diagnosis of gastric ulceration, but is also important for determning the effectiveness of treatment. When horses are treated with Gastrogard due to suspicion of gastric ulceration, gastroscopy is always recommended prior to the discontinuation of treatment to ensure complete resolution of the ulcers.
Treatment and Prevention
Treatment is aimed at minimizing the predisposing factors discussed above and decreasing acid production. When possible, horses should be allowed free-choice access to grass or hay. Environmental factors should also be addressed. Horses that must be stalled should be arranged so they can see and socialize with other horses.
Dividing the grain portion of the diet into more frequent, smaller feedings will help buffer the acid in the stomach. Decreasing types of grain that form volatile fatty acids, such as sweet feeds and some pelleted feeds, may help some horses. The energy from the grain may be provided using a commercially available high fat feed, or by feeding smaller amounts of grain with the addition of fats such as corn oil. In horses with lower caloric needs, free-choice grass hay with the appropriate vitamin and mineral supplements may be adequate.
Medication to decrease acid production is necessary in horses showing clinical disease or when the predisposing factors cannot be removed, such as with some horses in work or training. Although antacids are effective at reducing exposure of the stomach lining to acids, their effects are very short-lived and administration 6 to 12 times daily would be necessary. Antacids that are used as feed supplements are also relatively ineffective since they are ingested at the same time as the feed, which already will buffer the acid. Multiple medications are available to decrease acid production in the stomach. The most effective and convenient treatment is omeprazole (Gastrogard), which actually decreases acid production for up to 24 hours. Other medications that decrease acid production in the stomach include ranitidine and cimetidine, however, these medications are not proven to treat ulcers in horses and require more frequent administration. Gastroscopy is important to determine the location and severity of ulceration present, as ulcers in different portions of the stomach respond differently to treatment and different treatment recommendations may be given.
Prevention of ulcers before they occur is best. Limiting stressful situations, frequent feedings, careful diet selection, and free-choice access to grass or hay are best. When this is not adequate or possible, horses at greatest risk will benefit from medication to decrease acid production. Omeprazole (UlcerGard) has been shown to be effective at preventing the development of gastric ulcers in horses when predisposing factors cannot be avoided. Recently, SmartGut Ultra, a feed supplement made by SmartPak, has shown to help effectively prevent the recurrence of gastric ulcers following treatment.
If you have further questions, or would like to discuss gastric ulceration or treatment for your horse, please call Dr. Rachel Gardner at B.W. Furlong & Associates at 908-439-2821.