The equine stomach has two parts: an upper (squamous) region lined with epithelial cells that form a protective barrier and a lower (glandular) region that produces gastric juices, mucus, and other molecules important to digestion. Normally, a mat of food buffers the gastric juices in the lower region, minimizing splashing onto the squamous lining. Still, ulcers can develop in either region—equine squamous gastric disease (ESGD) or equine glandular gastric disease (EGGD)—and sometimes both at once. 

Although the two fall under the umbrella of equine gastric ulcer syndrome (EGUS), they are distinct diseases. “ESGD is primarily a management-based disease,” says Ben Sykes, BSc, BVMS, MS, MBA, Dipl. ACVIM, PhD, FHEA, a world-leading EGUS expert based in Australia. “Risk factors include inadequate forage, an excess of nonstructural carbohydrates, an excessive cumulative duration of exercise, and transport. In contrast, EGGD is primarily a stress-based disease and much more individual-horse-centric. Risk factors include breed, increased number of handlers/trainers/riders, and exercising five or more days a week.” 

Although veterinarians don’t usually consider ESGD stress-driven, hay intake—the main protective factor—depends on normal eating behavior. Horses must feel socially safe to eat properly. “Management factors that contribute to behavioral stress can also, indirectly, lead to an increased risk of ESGD via changes in eating behavior,” says Sykes. “These changes are often subtle and unobserved, leading to a false assumption that the provision of unrestricted access to forage automatically reduces the risk of ESGD. In actuality, it’s the consumption, not provision, of forage that reduces risk.” 

Equine gastric ulcer syndrome affects 50–70% of horses, impacting both welfare and performance. Signs of EGUS can include weight loss, poor hair coat, aversive ridden behaviors (especially in glandular disease), girthiness, and spookiness. 

Diagnosing EGUS: Gastroscopy and Biomarkers 

Gastroscopy remains the gold standard for diagnosing EGUS. The procedure involves a veterinarian passing an endoscope through the nasal passages into the stomach to observe its lining. But gastroscopy involves feed restriction and sedation, and repeated endoscopies can be stressful for the horse and costly for the owner. 

This has fueled interest in alternative approaches for detecting gastric ulcers in horses, such as biomarkers measured in blood or saliva. Researchers define biomarkers as measurable indicators of normal biological processes, pathogenic (disease or damage) processes, or responses to an exposure or intervention. Veterinarians can use them to make a diagnosis, determine susceptibility or a prognosis, or monitor treatment response. Reliable EGUS biomarkers could reduce the need for gastroscopy, predict at-risk horses, distinguish between ESGD and EGGD, and help guide treatment duration. 

Examples of EGUS Biomarkers in Saliva 

Despite their allure, few groups have studied salivary biomarkers in EGUS. “Salivary markers are appealing due to noninvasive collection, minimal training and equipment, limited animal stress, and rapid collection,” says Alberto Muñoz-Prieto, PhD, postdoctoral researcher at the University of Murcia, Spain. 

In 2017 researchers examined cortisol in saliva and found horses with EGGD had higher stimulated levels than those without. But follow-up was limited and, as Sykes notes, “cortisol/stress is common across many diseases,” prompting researchers to pursue more specific markers. 

Muñoz-Prieto and colleagues evaluated salivary biomarkers in 105 horses: those with EGUS, horses with EGUS-like signs but negative gastroscopy results, and healthy controls. The researchers collected the samples just before gastroscopy. 

They assessed markers including immune proteins (IgG, IgA, adenosine deaminase , S100 A8/A9, S100 A12), uric acid, ferric-reducing ability of saliva (FRAS), and advanced oxidation protein products (AOPP). 

“These are inflammatory and redox status (balance between oxidants and antioxidants) biomarkers and were selected because we wanted to evaluate how inflammatory biomarkers and biomarkers related to the redox status could change in EGUS,” says Muñoz-Prieto. 

Key findings from their research included: 

• They saw no differences in IgG, but salivary IgA was higher in horses with both ESGD and EGGD. 
• ADA was higher in all EGUS groups, especially EGGD. 
• S100 A12 and uric acid were elevated in all groups (including non-EGUS), though uric acid was surprisingly lower in EGUS horses than controls. 
• FRAS was higher in EGUS horses, particularly those with both ESGD and EGGD. 

“The next steps will be to do larger studies with a larger population and see if these biomarkers and other biomarkers previously described in saliva can be used as a help to detect and monitor EGUS,” says Muñoz-Prieto. 

“Correlation does not equal causation,” says Sykes. “So, while we might see differences in certain markers, it’s not necessarily directly related to the underlying cause. Sometimes we can explain the relationship … and sometimes we can’t, in which case the marker becomes a proxy.” 

He adds that biomarkers might also prove useful in monitoring healing: “If, for example, we can show that reductions in biomarker A consistently predict healing, then we could reduce the need for follow-up gastroscopy. Whether this relates to a single biomarker or interpretation of several in parallel is yet to be elucidated. But it’s a very interesting space, and we’re all excited to see how the science develops over time.” 

Take-Home Message 

Muñoz-Prieto says these findings “represent a promising foundation for the use of salivary biomarkers as analytical tools for helping on the detection of horses with gastric ulcers, highlighting their potential (as an) initial screening tool in clinical conditions.” However, researchers must first determine the efficacy of these tests in detecting EGUS before they can be applied in clinical practice.  

“Although promising, it’s too early to think that we’re going to pack up our gastroscopes and change over completely to biomarkers,” says Sykes. “More likely is that we’ll see them used as screening tests to guide further diagnostics, the same way that many tests are done in humans.”