Gastric ulcer syndrome is a common issue that affects the health and performance of horses. Horses with gastric ulcers suffer discomfort leading to poor health and performance, even progressing to sudden death if left unmanaged. Ulcer development is multifactorial involving stress and acid levels. We can use our knowledge of risk factors to minimize the occurrence of and to treat gastric ulcers to keep horses healthy and showing comfortably.  

In order to understand gastric ulcers, we must understand the anatomy of the horses’ stomach. There are two main regions of the stomach; the upper area lined by skin like tissue is the squamous section; the lower section producing acids for digestion is the glandular area. The squamous area is not designed to be in constant contact with acidic gastric fluid and is more often damaged at its junction with the glandular stomach. Acid exposure of the squamous area results from stomach content being pushed up by the abdominal pressure created by exercise. The glandular portion is injured when its defense mechanisms fail or are overwhelmed by acid levels. Long-term NSAID treatment such as Bute and Banamine can damage glandular protective mucosa.  

Exercise and training are proven risk factors for developing gastric ulcers with the prevalence and severity of ulcers increasing with training intensity. The highest prevalence of ulceration occurs in racehorses, with 80-100% developing gastric ulcers within 2-3 months of training. Still, 17-58% show horses and 37-59% of recreational horses are also affected. Stresses associated with competition including transportation, stall confinement, unfamiliar surroundings, and periodic feed restriction are linked to increased incidence of ulcers. Although ulcer prevalence and severity is greater in high performing horses, gastric ulcers affect horses of all disciplines and levels.

Diet composition, meal size, and feeding frequency affect saliva production, which buffers the acidity of the stomach. Unlike bile, which is constantly produced in the horse, saliva is only produced when horses chew. Horses on pasture will graze up to 18 hours a day, producing saliva and creating a buffered stomach environment for most of the day. Twice as much saliva is produced during consumption of forage versus grain. As well, grain and concentrates are rapidly fermented into acid during digestion. As such, a more continuous forage-based feeding pattern minimizes spikes in gastric acidity. 

Horses suffering from gastric ulcers may display clinical signs ranging from mild to severe, or may not exhibit any signs. Ulcer severity and prevalence does not necessarily correlate with clinical signs. We often see ulcer horses colic right after work, or after a grain meal when acid levels spike. Often clinically silent horses will begin to display signs with increased stress such as hauling, or a change in diet. Ulcers have been associated with ‘picky eating’, weight loss, poor hair coat, abdominal discomfort, sensitivity when girthing, bad attitudes and nervousness, often resulting in poor performance.  

Many horses will be presumptively diagnosed with gastric ulcers based on their symptoms, but ultimately diagnosis requires gastroscopy. Gastroscopy involves fasting the horse roughly 12 hours and then passing a long fiber optic camera though the nose into their stomach to visualize the stomach interior. Gastroscopy allows lesions to be localized and graded which will help guide treatment. 

Treatment involves decreasing the acid produced in the stomach and enhancing the stomachs protective mechanisms. Cimetidine or ranitidine blocks the signal for the acid producing cell, but it is short acting (1-2 hours). Comparatively, omeprazole stops the production of acid for longer (14 hours) by blocking acid pumps. As such, studies have shown omeprazole’s ability to prevent the development of and aid in healing horses’ gastric ulcers. Sucralfate protects the stomach lining by adhering to ulcerated mucosa. 

Omeprazole is available in compounded forms and patented GastroGard. Although the compounded forms are associated with positive results, omeprazole requires protection to prevent degradation in the stomach; GastroGard has a protective buffer. Treatment should continue for at least 3-4 weeks, and is often guided by clinical signs and repeat gastroscopy before cessation of treatment to ensure complete healing. Some horses may not show relief until ulcers are completely healed. It is important to recognize that at best 70-80% of lesions will heal within a 28-day omeprazole treatment period.  

Based on our understanding of ulcer development, appropriate husbandry practices should be employed to lower the risk of ulcers in horses. Free choice or frequent hay feedings (4-6 meals/day) might be a suitable replacement to pasture. Increasing forage availability using slow feed hay bags can mimic grazing and prolong access without excessive intake. Feeding alfalfa hay results in lower stomach acid levels than grass hay. Feeding forage before grain is helpful in stimulating the buffering activity before acid levels increase. Grain and concentrates should be fed as sparingly as possible. At minimum, providing more frequent, smaller concentrate meals throughout the day (>6 hours apart) is recommended.  

Medical therapy directed at healing and preventing gastric ulceration is successful only when partnered with management changes. Improvements in horse health directly impacts performance as horses are better conditioned and comfortable horses perform better. 

Editor’s Note: Original article written by Bailey Smith, DVM for the Arabian Horse Life Magazine.