Equine glandular gastric disease (EGGD), which causes ulceration in the lower, more protected area of the stomach, impacts horse performance and welfare considerably. Researchers have studied this condition for decades to better understand its mechanisms and develop new treatment methods.

Linda Paul, DVM, Dipl. ACVIM-LA, earned her PhD at Louisiana State University’s (LSU) School of Veterinary Medicine in biomedical and veterinary medical sciences, in Baton Rouge, in 2023 after she and her research team explored potential differences between the gastric microbiomes of healthy horses versus those with ulceration in the glandular portion.

Evaluating the Gastric Microbiome of Healthy vs. Ulcerated Horses

In this field study the researchers divided 57 horses into two groups. Group 1 consisted of 25 controls—horses without gastric ulcers. Group 2 was made up of 32 horses with mucosal disruption in the glandular part of the stomach (grade ≥ 2/4). Heidi Banse, DVM, PhD, Dipl. ACVIM-LA, associate professor of equine medicine at LSU, evaluated and scored the horses’ ulcers via gastroscopy, the gold-standard diagnostic method for equine gastric ulceration.

The researchers then biopsied the stomachs of all 57 horses, taking samples from healthy mucosa and from areas of glandular mucosal disruption, where applicable. They extracted bacterial DNA using a purpose-built commercial kit and found modest differences between the microbiota of the glandular mucosa in control horses and EGGD horses.

Specifically, they saw enrichments (growth) of the bacteria Actinomycetota, Staphylococcus, Lawsonella, and Streptococcus salivarius in control biopsy samples, while they found enrichments of Lactobacillus equigenerosi and Actinobacillus in EGGD ulceration samples.

Understanding Microbiome Differences in Horses

“The biological action of the enriched bacteria on the glandular mucosa for each group of horses is actually unknown,” said Paul—in other words, they don’t know its purpose. “For example, L. equigenerosi—found in this study in the EGGD ulcerations—was previously identified in horse feces. As a group, Lactobacillus species have various biological properties that can be good or bad.”

Banse recommends scientists conduct further research on the presence of L. equigenerosi in the equine glandular stomach to determine whether its presence has a positive, negative, or neutral impact on EGGD.

The Role of Exercise in EGGD

Beyond the gastric flora, Paul and her team also took a whole-horse look at potential risk factors for EGGD. They found that exercising more than three hours a week increased a horse’s risk of developing gastric ulcers.

The researchers are not sure why that’s the case. While researchers on previous studies have established that dietinfluences the gastric microbiome, exercise was not a factor directly associated with changes in the equine gastric microbiome in this study.

This lack of correlation suggests other mechanisms contribute to exercise’s influence on the development of EGGD, Paul said. She and her team hypothesized that decreased blood flow to the gastrointestinal tract during exercise makes the stomach more susceptible to dysfunction and disease.

Take-Home Message

Scientists need more research to draw definite conclusions from these preliminary findings. “Microbiome research is incredibly complex, especially when working with a population of client-owned horses at different barns, since different diet and management strategies can affect the gastric microbiome,” said Paul.

“Being able to identify bacterial differences between horses with and without EGGD in this study was nonetheless very exciting because we suspected from prior studies that differences existed,” she added. “Understanding those findings is another step forward in our comprehension of EGGD, a condition that impairs the athletic performance and overall health of so many horses.”