Prebiotic Reduces Leaky Gut Syndrome in Horses Under Stress

Researchers found that feeding a certain prebiotic product prior to transport and exercise reduced dysbiosis and leaky gut syndrome.

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The diversity of the gut microbiome plays an important role in managing stress in horses. | iStock
Gastrointestinal hyperpermeability, aka “leaky gut syndrome,” can cause poor performance, weight loss, and colic in horses. While clinical signs of leaky gut syndrome vary between horses, scientists have reported they are caused by increased permeability of the gastrointestinal tract, allowing potentially toxic compounds to leak into the bloodstream, causing an immune response. Researchers in Canada recently examined whether feeding a prebiotic product could help combat this problem.

Historically, researchers have found that acute or chronic stress can induce this increased intestinal permeability in horses, said Wendy Pearson, PhD, associate professor in Guelph’s Department of Animal Biosciences, a corresponding author on the study. The gut, particularly the diversity of its microbiome plays a significant role in managing stress; therefore, a dysfunctional gastrointestinal system could negatively impact horses’ health and well-being, she said.

Pearson and her fellow researchers investigated the impact of the fungal prebiotic on gastrointestinal hyperpermeability in a group of horses experiencing transport and exercise-related stress. The product was produced through a proprietary fermentation process involving Aspergillus oryzae, a type of fungus also used for making fermented foods such as soybean paste.

“We measured gastrointestinal permeability by feeding a compound, iohexol, that is normally too large to leak through the gut wall,” Pearson told “The horses were then trailered for 60 minutes immediately before undergoing moderate-intensity exercise for an additional 30 minutes.”

A. oryzae might be recommended for horses that undergo stressful events such as frequent trailering and exercise. The research team fed the product for one month prior to testing its effect, Pearson said. They observed the protective effect of A. oryzae after 30 days of supplementation.

“The stress challenge increased gut permeability to iohexol, which was seen in a significant increase in the presence of iohexol in the animals’ blood,” she said. “The fermentation product of A. oryzae almost completely prevented the increase in gastrointestinal permeability associated with the stress test.”

This research shows that dietary supplementation with A. oryzae could help prevent the gastrointestinal hyperpermeability associated with leaky gut syndrome. Pearson said she considers prebiotic supplementation a safe and cost-effective approach to protect horses from developing leaky gut syndrome, especially those prone to developing stress-induced leaky gut syndrome, such as show horses.

The study, “Dietary Fermentation Product of Aspergillus Oryzae Prevents Increases in Gastrointestinal Permeability (‘Leaky Gut’) in Horses Undergoing Combined Transport and Exercise,” appeared in the journal Animals in March 2023. It carried the following conflict-of-interest statement: “This study received funding from Biozyme Inc. L.W. is employed by Biozyme Inc. and had the following involvement in the study and writing—review and editing. All other authors declare no competing interests.”


Written by:

Tanja Bornmann is an equine scientist (MSc, University of Edinburgh, UK), licensed and qualified equestrian coach, writer, and published researcher. Through her business Academic Equitation, she offers her clients a science-based approach to horse training and management. You can follow Tanja on Twitter @academicequitat.  

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