Understanding The Development of Gastric Ulcers in Horses Part 1


Statistics indicate that up to 95% of Thoroughbreds in race training, 60% of show horses, 70% of endurance horses, 50% of foals with no visible symptoms, and 30–40% of non-performance horses have gastric ulcers.

Gastric ulcers or Equine Gastric Ulcer Syndrome (EGUS) in horses is a common health condition and is most often overlooked. These painful sores in a horse’s stomach lining can detrimentally impact their performance and overall well-being. In severe cases, they can cause perforation of the stomach lining and lead to fatal septic peritonitis, and colic. Equine Gastric Ulcer Syndrome (EGUS) can affect horses of all breeds and ages but is especially prevalent in performance horses such as equine eventers, racehorses and show horses.

3-meter gastroscope provided by the Center for Equine Health

Images of the stomachs of two horses were obtained by using a 3-meter gastroscope. The lining of a healthy stomach is shown on the left. The right image is of the same region of the stomach of a Thoroughbred racehorse with severe gastric ulceration. Image provided by the Center for Equine Health.

In this article, we will explore gastric ulcer development, signs of gastric ulcers in horses and the risks.

Signs of gastric ulcers in horses

  1. Poor appetite & picky eating
  2. Weight loss
  3. Deterioration of body condition
  4. Poor coat condition
  5. Behaviour changes
  6. Irritability, anxiety, aggression
  7. Depression
  8. Bruxism (grinding of teeth)
  9. Flehmen response (upper lip curl).
  10. Significant performance decline
  11. Digestive symptoms: acute or recurrent colic symptoms like rolling, pawing, and looking at their sides, or chronic diarrhoea.
  12. Stretching to urinate
  13. More time spent lying down


How Do Gastric Ulcers in Horses Develop?

Gastric ulcers develop when there is inflammation in the delicate lining of the horse’s stomach. This is usually caused by excessive exposure of the stomach lining to stomach acid which causes erosion of the protective mucosal layer and leads to painful ulcers.


5 Most Common Causes of Gastric Ulcers in Horses

1.    Intensive Horse Training

Equine gastric disease development is influenced by the frequency, duration, and intensity of exercise and training. Exercise-induced gastric ulcers are associated with various risk factors, including the following:

  • Whilst exercising, abdominal pressure and stomach contraction is increased. Especially in an unfed horse during exercise, acidic stomach contents are forced into acid-sensitive areas prone to ulcer development. Exposure to the acid causes acidification, inflammation, erosion and potentially ulceration.
  • During exercise, blood flow to the stomach is reduced, which slows the healing of the ulcer.
  • During training or competition, there may be long periods when the horses do not have access to feed. While the stomach is empty, the stomach acid cannot be buffered by food contents in the stomach.
  • Intensive training can also have a negative impact on the diverse gastro-intestinal microbiome which helps to protect the lining.
  • The physical and emotional stress caused by intensive training and competitive events promotes gastric ulcers.


2.    Equine Diet

  • Equine diets high in grain concentrates and low in hay roughage generate short-chain fatty acids, which may lead to cellular acidification, oedema, and ulceration.
  • Diets rich in sugars and starch like high-grain and high-snack diets, further increase the risk of ulcers, as these carbohydrates are rapidly fermented, producing increased acid byproducts and increasing the acid concentration in the stomach.
  • Grains for horses also do not require as much chewing as forage, and therefore less saliva is produced to help buffer the stomach acid, protecting the gastric lining.


3.    Equine Gastro-Intestinal Health Conditions

  • Delayed gastric outflow caused by other GIT health conditions like Pyloric Stenosis and Equine Glandular Gastric Disease.
  • Helicobacter pylori infection
  • Lower gastric microbe diversity as a result of gastric infections, diet and feeding frequency


4.    NSAIDS Ulcer Medicine for Horses

Nonselective Non-Steroidal Anti-inflammatory medication inhibits inflammatory mediators called prostaglandins, which reduces blood flow to the stomach. This results in a reduction of mucus-bicarbonate matrix production, which buffers stomach acid and protects the gastric lining, and leads to ulceration.




5.    Physiological Stress

Physical and emotional stress in horses has a significant impact on the equine digestive system. During stress, the release of the stress hormone cortisol is increased, which increases gastric acid production, reduces the regeneration ability of the protective glandular gastric lining, and diminishes protection against ulceration.

 Common causes of stress in horses include:

  • Exercise levels and Event performance
  • Transport
  • Stabling
  • Breeding and Pregnancy
  • Equine Diet
  • Illness
  • Pain and Injuries
  • Dehydration and heat-stress
  • Social Interaction


Equine Gastric Ulcer Complications

Gastric ulcers in horses pose several risks and can impact their overall health, well-being, and performance. These risks include:

1.     Deterioration of Body Condition:

Horses with gastric ulcers may exhibit a decreased appetite, leading to reduced food intake. Gastric ulcers can also lead to impaired nutrient absorption. This can result in weight loss and a marked deterioration of overall body condition.

2.     Potential complications:

Ulcers impact the normal digestive processes and may result in gastroesophageal reflux and esophagitis. Severe gastric ulcers can potentially lead to colic, haemorrhage (internal bleeding of the ulcer), perforation (destruction of the gastric lining with potential penetration of the ulcer into adjacent organs), or gastric outlet obstruction. Blood loss can result in anaemia and weakness.

3.     Behavioural Changes:

Horses with gastric ulcers may become irritable, anxious, or aggressive, which can negatively impact the delicate relationship between the horse and its handlers and riders.

4.     Significant Performance Decline:

Performance horses, such as racehorses, show horses, and eventers, may experience a significant deterioration in performance owing to the pain and discomfort associated with ulcers and the deterioration in overall body condition. Studies illustrate reduced aerobic capacity, stride length, and time to exhaustion. This can have huge financial and competitive consequences. Untreated or recurrent ulcers can limit the careers of racehorses and performance horses, making them less competitive while increasing the potential for early retirement.

5.     Dehydration:

Horses with gastric ulcers may have reduced water consumption, which can lead to dehydration and further impact their overall health.

6.     Stress and Anxiety in Horses:

Since equine gastric ulcers may significantly increase stress and anxiety in horses, it can exacerbate the condition even further and create a vicious cycle.

7.     Recurrent Ulcers:

Horses are more susceptible to recurring ulcers in the future if the underlying causes are not addressed.


In the next article, we will discuss comprehensive ulcer treatment for horses.

Part 2 of equine gastric ulcers, we learn about the signs and treatment for gastric ulcers in horses to empower horse trainers, owners and veterinary doctors who work in the equestrian sector.

You can also watch a video about the health supplements we have available for horses and the advantages it has to prevent or treat a variety of ailments here.


Our articles are written by Dr. Jeanne-Marie Lambrechts, an expert in the field of naturopathic medicine.  She has developed health supplements for pets, horses as well as people. 

UNTAMED’s animal health supplements are:

*100% Natural, with no additives, no artificial flavourings, no preservatives, no gluten, no sugar and no stimulants
*Certified & produced to highest standard
*Human-grade and of exceptional quality
*All our nutraceuticals are registered and can be claimed from medical aid funds
*UNTAMED is Tried, Tested and Trusted – Endorsed by Veterinary Doctors


  1. Jens Malmkvist, Janne Moller Poulsen, Nanna Luthersson, Rupert Palme, Janne Winther Christensen, Eva Sondergaard, Behaviour and stress responses in horses with gastric ulceration, Applied Animal behaviour Science, Volume 142, Issues 3–4, 2012, Pages 160-167, ISSN 0168-1591,
  2. Vokes J, Lovett A, Sykes B. Equine Gastric Ulcer Syndrome: An Update on Current Knowledge. Animals (Basel). 2023 Apr 5;13(7):1261. doi: 10.3390/ani13071261. PMID: 37048517; PMCID: PMC10093336.
  3. https://www.msdvetmanual.com/digestive-system/gastrointestinal-ulcers-in-large-animals/gastric-ulcers-in-horses#v11545467
  4. Lo Feudo CM, Stucchi L, Conturba B, Stancari G, Zucca E, Ferrucci F. Equine Gastric Ulcer Syndrome affects fitness parameters in poorly performing Standardbred racehorses. Front Vet Sci. 2022 Nov 25;9:1014619. doi: 10.3389/fvets.2022.1014619. PMID: 36504861; PMCID: PMC9732101.
  5. https://aaep.org/horsehealth/equine-gastric-ulcer-syndrome
  6. https://ceh.vetmed.ucdavis.edu/health-topics/equine-gastric-ulcer-syndrome

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