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Stomach ulcers

Stomach ulcers, also called gastric ulcers, in horses are quite common. The current estimate of prevalence is 90% in racehorses, 50% in foals, and 37-66% in sport and leisure horses. 

A portion of horses don’t show obvious symptoms at all, while others do, and sometimes owners don’t recognise the signs until after their horse has been treated.

Here’s what you should know…

The horse’s stomach

Unlike humans and many other animals, horses have a continuous production of stomach acid. This means that instead of producing more stomach acid when food is being consumed, the horse’s stomach produces acid continuously, whether or not there is food available. When the content of the stomach acidifies too much, this causes stomach ulcers. Normally, the acid is buffered by the saliva that’s swallowed when a horse eats. An adult horse produces about 35-40 litres of saliva every day. Regular saliva production keeps the stomach content from acidifying too much. The ancestors of our current day horses grazed almost continuously, so the continuous acid production in the stomach actually made their digestion more efficient. They wouldn’t have a break from grazing long enough for their stomachs to acidify. Research has shown that gastric ulcers can already start to form when a horse has no food for longer than 6 hours.

The top 3rd is lined with a squamous-cell lining, which contains no glands, minimal protective mechanisms and has no obvious functional role. The bottom 2/3rd is lined with glandular mucosa, which contains glands that produce hydrochloric acid (“stomach acid”). This glandular lining of the stomach also produces a bicarbonate buffering substance and mucus that coat and protect the glandular stomach lining in this bottom 2/3rd from the hydrochloric acid. The pH of the stomach in the top 3rd, squamous area is neutral (pH5-7). The pH in the middle, glandular area is slightly more acidic (pH4-5). The pH in the bottom 3rd, glandular area is very acidic (pH1-2). Food that passes the stomach passes through all these pH gradients as the hydrochloric acid breaks the food down. The top layer of the stomach’s content is most fibrous and least acidic, while the bottom layer has been broken down more and is densely mixed with acid liquid.

Equine Gastric Ulcer Syndrome (EGUS)

EGUS describes ulceration of the squamous stomach lining. Ulceration most commonly occurs where the squamous lining borders with the glandular lining. The squamous lining has no defence against acid and can therefore rapidly become ulcerated when the stomachs’ content at this squamous-glandular border becomes too acidic (pH below 4). As we’ve explained, this happens automatically if the stomach acid is not neutralized by saliva that’s produced as the horse eats.

Symptoms of EGUS may be various and often vague, and a proportion of horses doesn’t show signs at all. This can make EGUS very difficult to recognize. Possible symptoms of EGUS are reduced appetite, dullness, poor body condition/weight loss, behavioural issues (signs of discomfort or aggression when being saddled, girthed, or when being touched in the flank or stomach area), performance issues (reluctance to perform certain exercises, easily fatigued, reduced performance), horses may lay down a lot, grind their teeth or yawn excessively. In some cases, stomach ulcers may also lead to low grade colic. Colic is more common in foals with stomach ulcers. Possible signs of gastric ulcers in foals are excessive rolling, lying on their backs, restlessness, poor appetite or intermittent nursing, poor weight gain, teeth grinding, excessive salivation or diarrhoea.

What can cause EGUS?

Risk factors for developing EGUS are:

  • Low forage diets
  • High concentrate diets
  • Intermittent starvation
  • Water deprivation
  • Disease / hospitalization
  • Exercise intensity
  • Stress
  • Non-steroidal drugs

Diet and exercise

Studies have shown that ulceration is more common in horses fed twice daily (75%), than those fed three times daily (58%), and that periods of forage deprivation of more than 6 hours increases ulceration risk by 4x. Water deprivation increases ulceration risk by 3x.

Studies have also shown that the acidity of the stomach rapidly falls below pH4 during treadmill exercise, and abdominal pressure increases which compresses the stomach, bringing the squamous top 3rd into contact with stomach acid..

Stress and transportation

Research has proved that experimentally induced stress (travel, unknown environment, exercise) can rapidly induce ulceration, as can prolonged transport alone. It has also been found that a nervous demeanour predisposes to ulceration. Weaning can lead to stomach ulcers in both mares and foals. Anecdotal stories suggest that social stress from rehoming or death of a companion can lead to ulcers in some cases.


Non-steroidal drugs, such as phenylbutazone (“bute”) may cause gastric ulcers if used over prolonged periods of time and/or in higher doses. Some horses are more prone to develop stomach ulcers due to non-steroidal drug use than others. Meloxicam and firocoxib, a different non-steroidal drug, has shown to have a far lower risk of causing side-effects such as stomach ulcers than phenylbutazone. In horses prone to ulceration, horses that need high doses or prolonged therapy, it is suggested that meloxicam or firocoxib would be a better drug of choice.

Equine Glandular Gastritis Erosion Syndrome (EGGES)

EGGES describes ulceration of the glandular stomach lining. Ulceration most commonly occurs in the lowest part and close to the stomach’s exit. The glandular lining normally produces a mucus that defends it against acid. However, under certain circumstances this mucus barrier may fail. High doses or prolonged use of non-steroidal drugs has been associated with damage to the glandular lining. Certain bacteria that can be found in the horse’s stomach can attach to these lesions and inhibit healing. Stress may not only lead to EGUS, but can also lead to EGGES. Stress has been associated with decreased blood perfusion of the stomach and loss of natural stomach defences, which can result in stomach acid injury.

Symptoms of EGGES may also be various and vague, and are the same as for EGUS.


The only certain way of diagnosing stomach ulcers is by gastroscopy (looking inside the stomach with a camera). It allows us to identify and grade the gastric ulcers. Grading allows us to identify the severity of the situation and adjust therapy accordingly. Low grade ulceration may only need 3 weeks of a single-drug treatment, while severe ulceration may need 6 weeks or a combination of drugs and management changes.

Stomach ulcers are graded as follows:

  • Grade 0: Healthy stomach lining
  • Grade 1: The superficial layer (mucosa) is intact, but there are areas of redness or thickening.
  • Grade 2: Small, single or multiple lesions
  • Grade 3: Large, single or multiple lesions or extensive superficial lesions
  • Grade 4: Extensive lesions with areas of apparent deep ulceration

In some cases, in which symptoms are very indicative of stomach ulcers, therapy may be instigated without a gastroscopy. However, there are certain pitfalls to this approach. For instance, if there’s not enough improvement, was this because the horse is suffering from something other than stomach ulcers or because we didn’t treat long enough? When stomach ulcers are treated, initial improvement may be expected within 2 weeks. However, it should be clear that this does not mean that the stomach ulcers have resolved.

How is a gastroscopy done?

To be able to visualize the stomach properly, it needs to be fairly empty, so food is withheld for about half a day (usually from the night before). Then the horse is sedated to facilitate the horse’s comfort and better handling of the equipment. Then the gastro-scope is passed through the nasal passages into the oesophagus and stomach. Watch this short video on how a gastroscopy is done.

NB: Sometimes bots can be found in the stomach, in which case your vet will advise treatment.

Treatment and prevention

Stomach ulcers are treated with omeprazole, which may be combined with other treatments as well. Omeprazole lowers the pH of the stomach, which gives the stomach lining a chance to heal. There are commercially available products that contain omeprazole, however, these do not contain therapeutic doses. These products are only effective in the prevention of stomach ulcers, and NOT as treatment. Products that are effective in the treatment of stomach ulcers are only available through your vet.

Omeprazole may be combined with sucralfate, which forms a protective layer over the stomach lining to protect it from the hydrochloric acid. Sucralfate can therefore be useful when ulcers are located near or in the glandular bottom 2/3rd of the stomach.

By looking at what might have caused the ulcers we can also try to address the problem by making adjustments to the horse’s management. Diet, feeding practices and stress are the most common causes. Make sure your horse has access to enough palatable forage, doesn’t go without forage for more than 6 hours at any time, make use of (multiple) slow-feeder haynets when feeding hay (not in skinny horses) and look for any causes of stress. If stress is unavoidable, using a preventative omeprazole product during periods of stress (leading up to an event or transport for example) can be very helpful.

If you have a horse that’s prone to stomach ulcers, or you’re concerned your horse might have them, please contact us so we can help. Our vets can answer any questions, help you identify any risks for your horse and set you up with a plan.

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