Gastric ulcers in horses are one of the most frequently discussed subjects in equine health, and for understandable reasons. Few conditions have generated such a wide range of practical recommendations: forage availability, feeding intervals, starch reduction, turnout, buffering strategies, medication protocols, and management adjustments are all regularly addressed, and much of this guidance is both useful and scientifically well founded.
Yet despite this abundance of information, two situations continue to raise questions in everyday practice. Some horses develop gastric ulcers even when established feeding principles are already being followed. Others improve during treatment, only for the problem to reappear later, sometimes under management that appears unchanged. This is frustrating to both owners and veterinarians, let alone the horses who suffer the pain caused by their gastric ulcers.
Feeding strategies remain one of the central foundations of both prevention and treatment. But gastric ulcers in horses are influenced by more than feeding alone, and this becomes particularly apparent in horses that develop ulcers despite appropriate feeding strategies, or where disease returns after treatment. Among the additional management factors involved, stress deserves particular attention, especially in certain forms of gastric ulcers because its biological effects directly influence how well the stomach protects and repairs itself.
Understanding the Terminology Around Gastric Ulcers
Before looking more closely at how stress affects the stomach itself, it is worth clarifying one point, because the terminology around gastric ulcers in horses can seem confusing as several abbreviations are often used, although they do not all refer to exactly the same thing.
For many years, the broad term equine gastric ulcer syndrome (EGUS) was commonly used to describe ulcerative disease affecting the horse’s stomach as a whole. Today, this umbrella term remains useful, but clinical understanding has become more precise because it is now clearly understood that the two main regions of the stomach (the upper squamous region and the lower glandular region) not only differ anatomically and functionally, but that gastric ulcers also develop through different mechanisms in each of them. For that reason, current veterinary literature increasingly refers separately to equine squamous gastric disease (ESGD) and equine glandular gastric disease (EGGD).3
Why Different Parts of the Stomach Become Diseased for Different Reasons
To understand why these two forms of gastric disease develop differently, it is useful to first consider how gastric acid is produced and distributed within the equine stomach. Horses are unusual in that they produce gastric acid continuously, day and night, with a 500-kilogram horse producing up to around 60 litres of gastric acid over 24 hours. This acid is produced in the lower glandular region of the stomach.
The upper squamous region does not produce acid and lacks active protective mechanisms against prolonged acid contact. Instead, it relies largely on passive protection through the buffering effect of feed and bicarbonate-rich saliva, which help limit direct acid contact with its surface. This is why ESGD is strongly associated with prolonged fasting intervals, limited forage intake, high-starch feeding, and exercise-related acid contact.
The lower glandular region, by contrast, continuously produces gastric acid but also possesses specific active defence mechanisms to protect itself from that same acid exposure. The most important of these are mucus production and bicarbonate secretion, which form a protective surface barrier over the glandular mucosa. Ulcers can nevertheless develop in this region when these protective mechanisms become impaired, resulting in equine glandular gastric disease (EGGD). Among the factors now recognised to impair these protective mechanisms is chronic stress which is considered an important contributor to both the development and persistence of EGGD, whereas in equine squamous gastric disease (ESGD) its role in disease development remains less clearly defined.1
How Chronic Stress Affects the Stomach
This is one reason why chronic stress deserves particular attention in horses with glandular gastric disease: its effects are not limited to behaviour or general well-being, but directly influence how well the glandular stomach can maintain its protective barrier.
When stress becomes chronic, increased cortisol release and sustained activation of the sympathetic nervous system can reduce prostaglandin production, alter mucosal blood flow, and interfere with normal tissue repair. Over time, this weakens the mucosal defence system on which the glandular region depends, thereby increasing susceptibility to equine glandular gastric disease.
The Challenges of Addressing Chronic Stress
Understanding the physiological effects of chronic stress helps illustrate why chronic stress deserves serious attention in horses. However, addressing it is not always straightforward: the difficulty lies mainly in three areas.
First, stress is often physiologically present before it is clearly recognised. Horses are biologically adapted to minimise visible signs of vulnerability. As prey animals, they often continue functioning despite significant physical discomfort or emotional strain.
Second, behaviours linked to stress are often misinterpreted as something else: sensitivity, freshness, stubbornness, temperament, a strong personality, or simply the idea that this is just how that horse is. In many cases, signs that reflect stress are normalised rather than recognised as indicators that the horse is not coping as well as it appears.
Third, many of the situations capable of generating chronic stress are considered entirely normal from a human point of view. We often interpret the horse’s daily life through human logic and therefore easily underestimate how certain routines are experienced by an animal that remains biologically both a flight animal and a social animal. As a result, aspects of management, competition, transport, housing, handling, or training that appear familiar and well tolerated may still represent repeated stress for the horse, even when outward adaptation seems present. This is why a horse may receive appropriate feed and regular veterinary care, yet still experience chronic stress because important behavioural needs are not fully met, or because aspects of daily life repeatedly generate stress: for example, insufficient turnout, irregular schedules in feeding or exercise, prolonged individual stabling, changes in herd dynamics, conflict around resources, repeated transport, or inadequate training methods.
Chronic stress is recognised as one of the factors that may contribute to incomplete treatment response or recurrence of equine glandular gastric disease. In fact, current clinical reviews emphasise that successful treatment requires not only pharmacological therapy but also management aimed at reducing known risk factors, particularly physiological and psychological stressors (Rendle & Gough, 2025). 2
The changes required to address chronic stress are often multi-layered and can be more complex than they first appear. The first step is to examine closely the different aspects of that horse’s daily life, including daily routines, turnout structure, social environment, herd dynamics, handling, transport, and training methods, in order to identify potential sources of stress within those areas.
Once these sources of stress have been identified, the next step is to design practical strategies that reduce them as far as possible. This is often where things become more challenging, because some limiting factors may be beyond our control and/or cannot be fully changed. But many other aspects can often still be adjusted in ways that significantly reduce the amount of stress to which the horse is exposed.
When Gastric Disease Appears Even Though Nothing Has Changed in the Management
One point that often causes confusion is that horses may develop glandular disease even though they have lived under similar conditions for years without previous obvious problems. This does not necessarily mean that management plays no role. A horse is not the same biologically throughout life, and conditions that were tolerated for years may still become stressful later on. Age, workload, repeated experiences, changes in social environment, underlying discomfort, or other physiological pressures can gradually alter how well a horse copes with circumstances that previously seemed manageable. Horses are often able to compensate for certain deficits in lifestyle or ongoing stressors for a long time without showing obvious signs. But compensatory capacity is not unlimited. Over time, a point can be reached where that capacity is no longer sufficient, and the physiological effects of chronic stress begin to appear more clearly, including in the stomach. For that reason, the fact that a routine has existed unchanged for years does not automatically mean that it is not stressful for the horse today.
It is also important to remember that horses differ in how they cope with similar circumstances. Two horses may live under the same management and still respond very differently, because stress sensitivity, compensatory capacity, previous experiences, and physiological and mental resilience are not identical in every individual. That one horse develops glandular disease while another does not does not make the contributing management conditions irrelevant; it simply reflects individual differences in stress tolerance, resilience, and coping mechanisms.
Addressing Chronic Stress
Addressing underlying chronic stress often requires a willingness to question routines that have long seemed normal, to think outside the box, and to focus less on what looks acceptable from a human point of view and more on how the horse is actually experiencing daily life.
This does not mean that every horse with glandular disease is exposed to easily recognisable sources of stress, nor that relevant factors can always be identified quickly or reduced completely. But when gastric disease persists, recurs, or responds less predictably than expected, the horse’s daily life deserves deliberate attention. Looking carefully at how that horse is living, coping, and functioning can be an important part of a multimodal approach to the successful treatment of equine glandular gastric disease.
In some horses, recognising which factors are truly relevant requires a very individual look at daily management, behaviour, history, and the practical realities surrounding that horse. If you feel you would benefit from structured veterinary guidance to identify relevant contributing factors and translate them into practical decisions and management strategies, more information is available here: Individual Veterinary Guidance
References
- Klinck, M., Lovett, A., & Sykes, B. (2025). Incorporating a Behavioral Medicine Approach in the Multi-Modal Management of Chronic Equine Gastric Ulcer Syndrome (EGUS): A Clinical Commentary. Animals : an open access journal from MDPI, 15(20), 3019. https://doi.org/10.3390/ani15203019
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Rendle, D.I. & Gough, S.L. (2025) Pharmaceutical treatment of equine glandular gastric disease: A contextualised review of recent developments. Equine Veterinary Education, 37, 271–280. https://doi.org/10.1111/eve.14047
- Sykes, B. W., Bowen, M., Habershon-Butcher, J. L., Green, M., & Hallowell, G. D. (2019). Management factors and clinical implications of glandular and squamous gastric disease in horses. Journal of veterinary internal medicine, 33(1), 233–240. https://doi.org/10.1111/jvim.15350
- Vokes, J., Lovett, A., & Sykes, B. (2023). Equine Gastric Ulcer Syndrome: An Update on Current Knowledge. Animals : an open access journal from MDPI, 13(7), 1261. https://doi.org/10.3390/ani13071261