Horse Health Article - Gastric Ulcers
What are the latest updates in our understanding of equine gastric ulcer syndrome (EGUS), what are the predisposing factors, what is the prevalence, and what are the latest updates in treatments?
Equine Gastric Ulcer Syndrome (EGUS) is a commonly-occurring condition in horses and involves two major syndromes:
Equine Squamous Gastric Disease (ESGD)
Equine Glandular Gastric Disease (EGGD)
It is firstly important to establish a basic understanding of the horse’s stomach anatomy to better understand the two types of gastric disease occurring in horses. The horse’s stomach is divided into two parts: the squamous portion of the stomach, and the glandular portion of the stomach. A line known as the Margo Plicatus separates these two levels.
While digestive processes in the stomach involve acidic digestion, this occurs only within the glandular (acid-producing) portion of the stomach. The squamous portion is not designed to be exposed to acid, and is protected in horses with normal, fibre-rich diets by a fibrous mat which sits on the top of the stomach contents below the level of the Margo Plicatus.
A postmortem specimen of the equine stomach depicting the anatomical regions of the stomach - European College of Equine Internal Medicine Consensus Statement—Equine Gastric Ulcer Syndrome in Adult Horses (2015)
Equine Squamous Gastric Disease (ESGD) can most simply be described as ulceration of the squamous portion of the equine stomach, which most commonly occurs due to the acidic contents of the stomach splashing up against the squamous portion of the stomach walls (which are not designed to be exposed to acid). This makes this type of disease very common in racehorses (up to 100% of Thoroughbred racehorses in training) due to prolonged periods without fibre (due to intensive stabling) and subsequent high-intensity fast work.
The other, less well understood type of gastric disease occurring in horses is Equine Glandular Gastric Disease (EGGD.) What makes this type of disease interesting is that even though the mucosa of the glandular portion of the stomach is designed to be exposed to acid by the body’s own natural protective layer, for some reason this layer becomes disrupted, allowing acidic contents to penetrate into the mucosa and result in damage. EGGD is becoming more and more frequently studied, so prevalence data is not as readily available however in domesticated horses the prevalence of EGGD is understood to be between 59% - 79%.
What are the risk factors for gastric disease in horses?
The risk factors for Equine Glandular Gastric Disease (EGGD) are poorly understood, however some studies have revealed the following as potential risk factors for EGGD:
Greater than 5 days a week in work
Housing in single pens (reduced horse-horse contact)
Active competition season versus rest periods
There have not been clear nutritional risk factors that have been identified when it comes to EGGD. This is unlike ESGD, where restricted grazing, increased time between meals (i.e. long periods of fasting), and lower hay provision are all known risk factors.
What are the clinical signs of Equine Gastric Ulcer Disease (EGUS)?
Colic (especially colic/discomfort after eating)
Picky eaters (not finishing feed)
Poor performance
Behavioural changes (interestingly the research shows no association between “girthiness” and the presence of gastric ulcers)
Altered microbial populations (horses with EGGD have decreased variability of their microbiome than horses without EGGD)
It is worth noting that while NSAIDs (e.g. Bute) have been shown to increase risk of EGGD in fasted animals in some studies (Zuluaga, A.M. et al. 2016, Bishop, R. et al. 2022), other studies have not been able to demonstrate any increased risk from NSAID administration alone (Richardson, L.M. et al 2018.) However, it is important to note that concurrent administration of omeprazole and phenylbutazone in a recent study showed GI complications of up to 75% (Ricord, M. et al. 2020). As such the concurrent administration of bute and omeprazole should be avoided until we understand more about this relationship.
How do we diagnose Equine Gastric Ulcer Syndrome?
The only way to diagnose EGUS is via gastroscopy. Horses must be fasted for a minimum of 6-8 hours (longer if on a hay-based diet) to achieve full gastric emptying to allow visualisation of the pyloric antrum.
Faecal blood tests (e.g. Succeed Test) have been repeatedly shown to be inaccurate and unreliable for the diagnosis of both ESGD and EGGD.
What is the standard treatment for Equine Glandular Gastric Disease?
Despite the cause of EGGD being unknown, the pathologic process of acid damage to the glandular mucosa is the primary focus of treatment for the disease.
There are multiple common treatments that are used to treat EGGD:
Injectable Omeprazole (20mL Intramuscular Injections given every 7 days for 4-6 weeks)
Oral Omeprazole Paste (buffered formulation or enteric-coated granule suspension*) + Sucralfate (12mg/kg orally – given 30 mins after Omeprazole, 30 mins prior to feeding)
Oral Esomeprazole Paste* (given once daily 60 mins before feeding)
Oral Omeprazole Granules (Equestra Granules - given in a small amount of feed 30 mins prior to feeding)
* Buffered formulations (e.g. Ulcershield) have decreased bioavailability in non-fasted horses compared to enteric-coated granule formulations (e.g. Gastrozol) or Esomeprazole. As such, horses that are not able to be fasted for a minimum of 4-6 hours prior to Omeprazole are recommended to receive either the injectable preparation or enteric-coated granule formulations (either suspension or in-feed granules)
Unlike in humans, rebound acidity in horses being treated with PPI’s (proton-pump inhibitors e.g. Omeprazole) following discontinuation of treatment is not as clinically significant. While horses do show rebound increases in gastric hyperacidity for a maximum of 72 hours following discontinuation of therapy, which has been shown to cause recurrence of ESGD (squamous ulceration) in Thoroughbred racehorses, the risks of glandular or squamous disease recurring within this period are likely able to be minimised by the provision of adequate fibre and minimising stressful events (e.g. transport/housing changes) during this period (Vokes, J. et al. 2023, Sykes et al. 2023.)
Allowing horses to practice normal social behaviours such as mutual grooming is believed to contribute to stress reduction - minimising the risk of glandular gastric disease.
What does the research say regarding feeding/supplements/management?
All horses should receive an absolute minimum of 2% bodyweight per day of fibre (unless being treated for hyperinsulinaemia/other conditions as discussed with a veterinarian)
Feeding even 300g of Lucerne Hay before exercise has been shown to be effective to reduce acid splash during work
Ideally horses should receive a minimum of 2 (preferably 3) complete rest days
Housing horses to allow for increased horse-horse contact (e.g. allowing normal social behaviour) is likely to reduce stress – a potential cause of EGGD
Feeding a fish-based Omega-3 product is likely to have an effect on mediating gastric disease (extrapolated from human data)
Feeding pectin-lecithin rich feeds has been shown to improve both ESGD and EGGD (e.g. beet pulp products such as Speedibeet)
Kelato GastroAID Recovery has been shown to prevent the recurrence of ESGD in a clinical trial following cessation of Omeprazole, despite rebound gastric hyperacidity!
Probiotics have been shown to reduce anaerobic bacteria and increase bacterial diversity within the microbiome (especially Saccharomyces cerevisiae)
Licorice root extract alone, as well as in combination with other ingredients, has been shown to reduce EGGD in some studies