Prebiotics may not be good for stomach health in horses, research suggests

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The impact on stomach health should be carefully considered before feeding a prebiotic to horses, according to researchers.

Prebiotics are often added to horse feed in order to stabilise the horse’s health. They are indigestible fibres that can stimulate the growth and activity of certain beneficial bacteria in the large intestine.

“Horses have a relatively small, non-diverse core microbiome and are therefore very susceptible to digestive disorders,” explains Professor Annette Zeyner, head of the animal nutrition group at Martin Luther University Halle-Wittenberg in Germany.

However, according to Zeyner, insufficient research has been conducted on whether the use of prebiotics actually produce the desired effects.

Her research group explored this question in partnership with Professor Gerhard Breves’ laboratory from the University of Veterinary Medicine Hannover, also in Germany.

The researchers found that the prebiotic assessed, Jerusalem artichoke meal, which is a typical natural prebiotic compound for horses, was only able to help stabilize the intestinal flora of horses to a limited degree.

The evidence suggests that, before they can reach the intestines, prebiotics may well partially break down in the animals’ stomachs, which can lead to inflammation of the stomach lining.

The researchers suggest that prebiotic food supplements should be prepared so that they don’t take effect until they reach the large intestine.

For their research, the team focused on the effects of feeding Jerusalem artichoke.

In addition to their normal feed, six animals received the meal, which contains high amounts of certain carbohydrates, so-called fructo-oligosaccharides and also inulin.

Another group of six horses received a placebo with their normal feed.

After 21 days, the researchers analysed the balance of bacteria in the digestive tract of the animals in both groups.

Jerusalem artichokes.
Jerusalem artyichokes. By Gilabrand at English Wikipedia, CC BY-SA 3.0.

The feeding of this prebiotic compound was found to have an impact on the microbial community across the entire gastrointestinal tract.

The researchers discovered that the prebiotics were already being fermented in the stomach by the microorganisms naturally living there — that is, they were taking effect much too early.

“The fermentation process leads to the formation of organic acids that — unlike in the large intestine — can damage the mucous membrane of the horse’s stomach,” says Maren Glatter, a member of Zeyner’s group and lead author of the study.

However, the bacterial diversity of the entire digestive tract did increase, which probably also produced the desired protective effect.

“Still, the prebiotics are probably more harmful than beneficial when used in their present form,” Zeyner surmises.

Instead, the substances must be treated so that they arrive in the large intestine in one dose in order to have a positive effect on the intestinal bacteria living there without stimulating overactivity.

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“The effect on the bacterial community in the foregut (especially the stomach) was more pronounced in comparison to the effect in the hindgut,” the authors reported in the open-access peer-reviewed journal, PLOS ONE.

“Therefore, the impact on stomach health should be carefully considered.”

The researchers said fecal samples are used in most studies to assess the impact of prebiotics on the large intestine microbiota, which meant that other parts of the equine gastrointestinal tract are not routinely taken into consideration.

They said the feeding of prebiotic active compounds aims to stimulate the metabolism of the naturally present microbiota, mainly in the large intestine.

“Despite the large intestine being the declared target for prebiotic interventions, the results of this study show a clear effect in the foregut.”

The supplementation of Jerusalem artichoke meal containing prebiotic fructooligosaccharides and inulin increased the relative abundance of the dominant genus Lactobacillus and decreased the relative abundance of Streptococcus to a marked extent in the stomach.

“This alteration might cause a harmful impact on the stomach by increased bacterial metabolism … and possibly a decreased pH value.”

“Feeding Jerusalem artichoke meal nevertheless increases the bacterial diversity in all parts of the digestive tract, which might be beneficial for the stability of the gastrointestinal microbial community.”

Glatter M, Borewicz K, van den Bogert B, Wensch-Dorendorf M, Bochnia M, Greef JM, et al. (2019) Modification of the equine gastrointestinal microbiota by Jerusalem artichoke meal supplementation. PLoS ONE 14(8): e0220553. https://doi.org/10.1371/journal.pone.0220553

The study, published under a Creative Commons License, can be read here

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