Researchers have linked a bacterium with gastric ulcers in horses, although they stress that their findings do not show that the pathogen causes the stomach problems.
The pathogen, Sarcina, has been linked to slow gastric emptying in humans.
Sarah Voss and her colleagues at the University of Glasgow said there is growing evidence that changes in the gastrointestinal microbiota occur in many disease processes in the horse. For example, rapid changes in the faecal microbiota have been shown in colicky horses.
Equine gastric ulceration syndrome (EGUS) is commonly diagnosed in horses. It has two forms – equine squamous gastric disease (ESGD), which affects the upper non-acid-producing part of the stomach; and equine glandular gastric disease (EGGD), which affects the lower acid-producing portion.
ESGD and EGGD are distinctly different diseases. The researchers noted that the reasons for the development and progression of the form affecting the upper stomach are well established, as are the risk factors and treatment options.
However, the development and progression of EGGD in the lower stomach, and the role of the gastric microbiota, are poorly understood. There is also a higher rate of treatment failure.
The study team, writing in the Journal of Equine Veterinary Science, set out to investigate whether the glandular gastric microbiota is altered in horses with EGGD.
Five Thoroughbred racehorses from one training center underwent gastroscopic examinations as part of a poor performance investigation.
Samples were taken from EGGD lesions and nearby normal stomach lining. The samples underwent molecular-based testing to identify the microbiota. The same horses were sampled again six months later.
The study team found that normal glandular stomach-lining samples had a higher proportion of Proteobacteria than the nearby ulcerated stomach lining. Further, the relative abundance of Firmicutes was lower in samples from normal stomach lining than the lesions.
Analysis revealed that the greater proportion of Firmicutes in ulcers was due to a very high relative abundance of Sarcina (up to 92.4%) in two horses with EGGD.
“Although our results do not provide evidence for bacterial causation of EGGD lesions, we have identified a novel association between Sarcina and EGGD lesions in horses,” Voss and her colleagues reported.
This, they said, is of interest because of the involvement of Sarcina in gastric disease in other species. “An association has been made between delayed gastric emptying rate and Sarcina abundance in humans,” they noted.
They said that an increased cortisol stress response has been recognised in some horses with EGGD, and increased cortisol production is thought to prolong gastric emptying time in this species. “It may be valuable to further investigate the relationship between glandular ulceration and gastric emptying rate in horses.”
Discussing their findings, the authors said Sarcina was also identified in normal mucosal samples in the study, but amounted to just 0.2% of the counts. This suggested it may be part of the normal gastric microbiome, with excessive proliferation under certain conditions.
They acknowledged that one limitation of their study was the low overall sample number and a low number of horses with EGGD in particular.
Nevertheless, the study produced good preliminary evidence for the involvement of Sarcina in EGGD. They said larger scale studies are required to further understand the potential role of this and other bacteria in the development and progression of the disease.
“Collecting a greater number of samples from each horse would be beneficial; however this is limited by the welfare implications of prolonging diagnostic procedures such as gastroscopy.”
They said their findings suggest that different horses have a different gastric microbiota composition.
“As it is probable that the gastric microbiota is widely affected in diseased stomachs, future studies should seek to include horses without EGUS.”
They said there is a need for longer-running microbiota studies. “An understanding of the dynamic of the microbial population over time will aid with interpretation of data from cross-sectional studies, which are more commonly performed.
“This is particularly pertinent when investigating the gastrointestinal microbiota of horses, which commonly experience seasonal dietary changes, which may reasonably be expected to affect the gastrointestinal microflora.”
Further investigations of the inter-relationship between factors identified in the study and the gastric microbiome may improve understanding of the cause of EGGD, they said.
The study team comprised Voss, David McGuinness, William Weir and David Sutton, all from the University of Glasgow’s veterinary school.
Sarah J. Voss, David H. McGuinness, William Weir, David G.M. Sutton. A study comparing the healthy and diseased equine glandular gastric microbiota sampled with sheathed transendoscopic cytology brushes, Journal of Equine Veterinary Science, Volume 116, 2022, 104002, ISSN 0737-0806, https://doi.org/10.1016/j.jevs.2022.104002.