Understanding the Modern View of Equine Gastric Ulcers
Written by Mishel Metcalf for Hi Form Australia 2026
For nearly three decades, the term Equine Gastric Ulcer Syndrome—EGUS—has been used to describe a collection of painful conditions affecting the horse’s stomach. As veterinary research has evolved, so has our understanding of what those ulcers actually are. Today, EGUS is no longer considered a single disease, but rather two distinct conditions: Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD).
This modern distinction helps owners and veterinarians make more accurate diagnoses and implement more effective management strategies.
A Stomach Divided
The equine stomach is unique in its structure and function. It is divided into two regions by a visible line known as the margo plicatus.
Below this line lies the glandular region, a highly active area responsible for producing gastric fluids. These secretions—hydrochloric acid, pepsinogen, bicarbonate and mucus—play a critical role in digestion. The pH in this region typically sits around 2.9, though it can swing from under 2 to over 6 depending on when and what the horse last ate.
Pepsinogen, once mixed with acid, becomes pepsin, the enzyme responsible for breaking down dietary protein. After the feed is liquefied and properly mixed, it is pushed through the squamous region of the stomach, then exits through the pylorus into the duodenum to continue digestion.
Above the margo plicatus is the squamous region, a completely different type of lining. Unlike the glandular area, it has no protective mucus or buffering system, making it far more vulnerable to the corrosive effects of acid.
How Ulcers Develop
Although horses have evolved to handle the near-constant flow of acid in their stomachs, modern management practices can disrupt the delicate balance between acid production and natural protection.
EGGD: When Protection Is Overwhelmed
The glandular region does have built-in defences—namely mucus production and bicarbonate secretion. But these can be overwhelmed when acid levels rise, particularly in horses under stress or those with inconsistent feeding patterns. When this protective layer fails, ulcers or lesions begin to form along the glandular mucosa.
ESGD: An Unprotected Zone
The squamous region is far more vulnerable. Because it lacks any natural barriers, when acidic contents splash or pool against this upper area—often during fasting periods or exercise—damage can occur quickly. This is the form of ulceration most commonly seen in performance horses.
What the Research Tells Us About Risk
Although scientists continue to explore the roles of breed, age, workload, travel, social environment and housing, there simply aren’t enough robust studies yet to reliably identify which types of horses are most predisposed to EGUS.
But in one area, the research is detailed: nutrition plays a decisive role.
Feeding routines influence the horse’s gastric environment more than any other modifiable factor. Long gaps between meals, high-starch diets, and practices that limit forage availability all increase acid exposure, particularly in the squamous region. Conversely, turnout, movement, and fibre-rich, frequent feeding support a more stable stomach pH and reduce the risk of ulceration.
Why Understanding Acid Matters
At the heart of both ESGD and EGGD is the behaviour of gastric acid—how it is produced, where it pools, how it moves, and how often it comes into contact with unprotected tissue. This is why a solid understanding of gastric physiology is essential for every horse owner, whether caring for a retired companion or managing a competition athlete.
By appreciating the differences between the glandular and squamous regions—and the unique vulnerabilities of each—we can make informed choices about nutrition, training, turnout, and general husbandry. And with that, we can meaningfully reduce the risk of a condition that continues to affect horses worldwide.
Hi Form nutrition that supports horses with ESGD and EGGD
Equicubes are natural long-stemmed fibre complete feeds, containing daily nutritional requirements in the form of a hay cube. Equicubes increases chewing time, therefore generating more saliva for acid buffering, and leaves the stomach full for longer.
BioEquus Gold is specially formulated to support a healthy gut microbiome and digestive system, particularly in horses diagnosed with or prone to ulcers and other digestive disorders. BioEquus Gold contains a powerful blend of prebiotics and probiotics, which work together to encourage the growth of good bacteria in the gut.
