Withholding feed for 10 hours or more has a big effect on gut bacteria in horses, findings suggest

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Fasting or withholding feed is a common confounding factor that is likely to influence the gut microbiota, according to researchers.
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Withholding feed has a significant effect on the diversity and composition of the faecal bacterial microbiota of horses, particularly after 10 hours, researchers report.

Jaclyn Willette and her fellow researchers said there is an association between equine gastrointestinal disease-causing colic signs and changes in the faecal bacterial microbiota.

The reasons for these changes and their clinical relevance has not been investigated, they noted.

The researchers, with the New Bolton Center at the University of Pennsylvania, said withholding feed, which is an integral part of managing horses with colic, may contribute to the observed changes in the microbiota. This, in turn, could affect the interpretation of findings in horses with colic.

The study team set out to determine the effect of withholding feed for 24 hours on equine faecal bacterial microbiota in healthy mares to differentiate the effects of withholding feed from the changes potentially associated with the disease.

The mares, aged 14 to 23, comprised of three Standardbreds, two Thoroughbreds, a Quarter Horse, an Irish Sport Horse, and a Morgan. In the crossover study design, the horses were randomly assigned to two groups, one of which was fed as normal to serve as the control.

Fecal samples – 392 in all – were taken for analysis at regular intervals during the 24 hours, and also during the period afterwards, when feed was reintroduced.

The researchers found that species richness and diversity were significantly lower 10 to 24 hours after withholding feed, and in the two to 12 hours after feed was introduced, compared to samples taken from the control group.

Restoration of species richness and diversity began to occur 18 to 24 hours after feed was reintroduced.

Horses having feed withheld had a distinct bacterial population compared to fed horses, they reported. Bacteroidetes BS11 and Firmicutes Christensenellaceae, Christensenella, and Dehalobacteriaceae were significantly increased in horses whose feed was withheld, primarily during the late-withheld and early-refed time points.

Bacteroidetes Marinilabiaceae and Prevotellaceae, Firmicutes Veillonellaceae, Anaerovibrio, and Bulleidia, and Proteobacteria GMD14H09 were significantly decreased in horses with feed withheld at late-withheld, early-refed, and late-refed time periods.

Changes in commensal gut microbiota were not significant between groups.

Discussing their findings, the study team said the gastrointestinal microbial communities colonizing the caecum and colon play important roles in feed digestion, offer protection from pathogen invasion, maintain the integrity of intestinal epithelium, and promote immune responses.

“While efforts to understand the composition of microbial communities colonizing the equine gastrointestinal tract have provided insights on the presence of core microbiota in horses, the functional relevance of the individual populations and their sensitivity to external perturbations such as changes in diet, management, incidence of diseases, and therapeutic interventions are not very well understood.”

Fasting or withholding feed is a common confounding factor that is likely to influence the gut microbiota, they said.

The authors said their findings indicate that access to feed may be a contributing factor to changes in microbiota which may be confounded in gastrointestinal related disorders such as colic.

“That being said, alterations in the microbiota composition and relative abundance of specific phyla and genera may be more relevant to gastrointestinal disease.”

The researchers concluded that withholding feed has a significant effect on faecal bacterial microbiota diversity and composition, particularly following at least 10 hours of withholding feed. “Diversity and composition began to return toward normal within 24 hours of re-introducing feed.

“The effect of withholding feed should be taken into consideration when interpreting data on the equine faecal bacterial microbiota in horses.”

The New Bolton Center study team comprised Willette, Dipti Pitta, Nagaraju Indugu, Bonnie Vecchiarelli, Meagan Hennessy, Tamara Dobbie and Louise Southwood.

Willette, J.A., Pitta, D., Indugu, N. et al. Experimental crossover study on the effects of withholding feed for 24 h on the equine faecal bacterial microbiota in healthy mares. BMC Vet Res 17, 3 (2021). https://doi.org/10.1186/s12917-020-02706-8

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

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