Withholding feed from healthy horses for at least 10 hours brings about significant changes in the bacterial microbiota of their gut, researchers report.
The association between gastrointestinal disease and the faecal bacterial microbiota is an area of active research across many species.
Humans and cattle with chronic gastrointestinal disease have a decrease in bacterial species richness and diversity compared to healthy subjects.
Gastrointestinal disease may result from the disruption of complex interactions between the host and the gut microbiota.
Recently published research has revealed that horses hospitalised for colic had significantly decreased faecal or colonic bacterial species richness and diversity on admission.
Their bacterial gut population was found to be quite distinct compared to horses admitted to hospital for elective surgery.
It is plausible that alterations in the faecal microbiota may be associated with intestinal problems and inflammation leading to signs of colic, Jaclyn Willette and her colleagues at the New Bolton Center, part of the University of Pennsylvania, reported in the journal BMC Veterinary Research.
However, there are many possible reasons for such changes. Withholding feed is an integral part of managing horses with colic.
Horses showing colic signs are likely to have had feed withheld before admission to referral hospitals, whereas horses admitted for an elective surgical procedure may not have had feed withheld.
Withholding feed may affect the faecal microbiota, and its effect needs to be determined in healthy horses to better interpret studies on the microbiota of horses with colic, the researchers said.
For their research, the researchers set out to determine the effect of withholding feed for 24 hours on the equine faecal bacterial microbiota of eight healthy mares in a crossover study design.
The mares, all owned by the New Bolton Center, were returned to their herd following the experiment.
During their fasts, they had free access to water. All received a little 170-gram snack of commercial feed every six hours during their fast for humane reasons.
At the end of the fast, the horses were reintroduced to free-choice timothy hay.
The researchers found that species richness and diversity were significantly lower 10 to 24 hours after the fast began, which persisted for 2 to 12 hours after hay was reintroduced to the diet.
Restoration of species richness and diversity began to occur 18 to 24 hours after the reintroduction of feed.
Horses having their feed withheld had a distinct bacterial population compared to fed horses, they found.
Bacteroidetes BS11 and firmicutes Christensenellaceae, Christensenella, and Dehalobacteriaceae were significantly increased in horses withheld from feed, primarily toward the end of the fast and early re-feed time points.
Bacteroidetes Marinilabiaceae and Prevotellaceae, firmicutes Veillonellaceae, Anaerovibrio, and Bulleidia, and proteobacteria GMD14H09 were significantly decreased toward the end of the fasts, and in the hours that followed the reintroduction of feed.
“Withholding feed has a significant effect on faecal bacterial microbiota diversity and composition particularly following at least 10 hours of withholding feed,” they concluded.
Diversity and composition began to return toward normal within 24 hours of re-introducing food.
“The effect of withholding feed should be taken into consideration when interpreting data on the equine faecal bacterial microbiota in horses,” they said.
The researchers, discussing their findings, noted that, in their previous work, they identified five bacterial genera that significantly increased and nine genera that decreased in horses that were admitted to hospital for colic compared to horses admitted for an elective procedure.
While these results were interesting, they concluded that several other factors, including withholding feed, may contribute to the changes in horses with colic.
“BS11 and unclassified Christensenellaceae were significantly increased in horses presenting for colic and horses withheld from feed in the current study, indicating that an increase in these specific bacteria may be attributed to withholding feed and not colic alone.
“In contrast, increases in Streptococcus and Sphaerochaeta were unique to horses presented for colic and were not observed in this study, indicating that colic is associated with changes in specific genera.”
Such findings are important in designing experiments to fully understand the role of these specific bacterial populations in colic, they said, and may suggest markers for developing therapeutic interventions.
The study team, all with the New Bolton Center, 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