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Treating Equine Gastric Ulcer Syndrome with Omeprazole

Equine gastric ulcer syndrome (EGUS) is a common condition among performance horses, with a high prevalence rate of up to 90% in racehorses and over 50% in foals. Fortunately, omeprazole, an FDA-approved drug, has been proven to be effective in treating EGUS. In this article, we will explore the various aspects of omeprazole treatment for EGUS, including how it works, how to optimize its effectiveness, and how to prevent recurrence.

Understanding EGUS

Before delving into the details of omeprazole treatment, it's important to understand what EGUS is and how it develops. EGUS is characterized by sores or lesions that develop in the intestinal lining of horses, specifically in the stomach. These ulcers can cause horses to become girthy, resistant to training, agitated, and generally irritable.

The cause of EGUS is often multifactorial, meaning that several interacting risk factors can cause ulcers to develop. These risk factors include diet, exposure to stress, workload, and environment. The stomach of the horse is a highly acidic environment, with proton pumps continuously producing acids such as hydrochloric acid (HCl) to aid in the breakdown of food. This process occurs whether or not there is food in the stomach to digest. Over a single day, a typical 500 kg (1100 lbs) horse can produce up to 60 liters (16 gallons) of gastric acids.

The equine stomach is divided into two sections: the upper squamous region and the glandular region. Ulcers in the glandular region are much more difficult to heal than those in the squamous region.

How Omeprazole Works to Treat EGUS

Omeprazole is a proton pump inhibitor medication that suppresses the production of stomach acid. It temporarily reduces the acidity of the stomach, making it an effective treatment for EGUS. When given to horses, omeprazole works by inhibiting the body's acid producers, the proton pumps. However, because omeprazole is a prodrug, it's not active when it's administered and requires activation through the digestive process. This occurs when the proton pumps get turned on when the horse eats.

Omeprazole is sold under the tradenames GastroGard and UlcerGard and is used to prevent or treat EGUS. Treatment for gastric ulcers can be a long and expensive commitment. Following treatment, there is a risk of ulcer recurrence unless changes in the horse's management and feeding program are made. Horse owners should be aware of how omeprazole works to prevent and heal ulcers, as well as any complications that could occur with treatment, such as rebound acid hypersecretion (RAH).

Optimizing Omeprazole Treatment for EGUS

While omeprazole is an effective treatment for EGUS, there are ways to optimize its effectiveness. According to an equine internal medicine specialist, feeding horses strategically can make omeprazole even more effective, leading to higher success rates for both squamous and glandular ulcer cases.

Specifically, when horses are fasted overnight and then fed hay an hour after their morning treatment of omeprazole, the stomach's conditions are ideal for optimizing the therapy's methods of action. This fasting protocol is particularly important with glandular ulcers, as they respond relatively poorly to oral omeprazole and are much harder to treat, probably because they appear to require much greater acid reduction to heal than squamous ulcers. Horses naturally fast overnight, and when the omeprazole is administered on this empty stomach in the early morning, it's better absorbed. Omeprazole works by inhibiting the body's acid producers, the proton pumps. However, because omeprazole is a prodrug, it's not active when it's administered and requires activation through the digestive process. This occurs when the proton pumps get turned on when the horse eats. Giving the omeprazole about an hour to get absorbed into the horse's system and then feeding a large breakfast of hay that gets as many proton pumps turned on as possible means the timing lines up for having a maximum amount of active drug inhibiting the maximum number of proton pumps. Owners might be reluctant to fast horses with ulcers, because an empty stomach is a risk factor for ulcer development. However, horses naturally fast for a few hours in the night as they sleep, and their stomachs take a few hours to empty completely once they stop eating. So, removing their hay at 10 p.m. and giving them breakfast at 8 a.m., an hour after the 7 a.m. treatment, simply represents an enforced version of their natural nighttime fast. Importantly, the fasting is for a good cause, as it results in a much more potent medication that leads to better and more thorough ulcer healing.

Dosage and Administration

The recommended dosage for omeprazole is 4 mg/kg bwt per os, once daily, for 28 days. After 28 days, the dosage can be reduced to a half dose of 2 mg/kg bwt once daily. Combination therapy with sucralfate is still recommended for glandular disease.

Monitoring Treatment

Monitoring the effectiveness of omeprazole treatment for EGUS is essential to ensure successful healing and prevent recurrence. Endoscopic examination is the gold standard for assessing the healing of gastric ulcers. Horses with healed ulcers should be re-evaluated endoscopically after a few weeks to ensure that the ulcers have not recurred.


In conclusion, omeprazole is an effective treatment for EGUS in horses, but strategic feeding and dosage administration can optimize its effectiveness. Horse owners should be aware of the risk factors for EGUS and take steps to prevent its development, such as reducing stress, providing a balanced diet, and ensuring adequate turnout. With proper management and treatment, horses with EGUS can make a full recovery and return to their performance activities.

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