Management Significantly Affects Foals’ Gut Microbiota

Are your foals outside full-time with their dams? Or do you keep your breeding stock indoors with occasional pasture access? The answers to these questions might have consequences on your foal’s digestive health, even on a microscopic level.

In a new study, young foals raised as members of a free-roaming herd had a vastly more varied hindgut microbiome than those raised in stalls with regular turnout. The results suggest that even in the first six weeks of life, when foals are still mostly nursing, management affects horses’ gut microbiota, said Meredith Tavenner, MSc, of the Department of Animal and Food Sciences at the University of Delaware, in Newark.

“It’s too early to give specific recommendations, but this study really broadens our understanding of how management affects the hindgut,” said Tavenner, whose work was supervised by Amy Biddle, PhD, also of the University of Delaware.

“The beauty of (this research) is that it’s solid ground-floor work that draws attention to the delicate issues we’re dealing with in regard to the equine gut microbiome,” said Sue McDonnell, PhD, an equine behavior specialist at the University of Pennsylvania’s New Bolton Center, in Kennett Square. In particular, it points to how feed and exposure to other animals, or even to humans, might affect the microbiome—for better or worse.

Rectal Swabs From Domestic Breeding Center Foals and ‘Wild’-Managed Foals

Tavenner and her fellow researchers ran DNA analyses on samples from rectal swabs on 20 foals, collected once a week for five to six weeks after birth. Half the foals were Standardbreds, raised in a “traditional” breeding setting in which the foals and their dams spent the first week in a stall and subsequent weeks with limited paddock turnout with a second mare-foal pair. They were allowed full pasture turnout starting at 45 days of age (which corresponded with the end of the study period).

The other foals were Shetland-type ponies living as a semi-feral herd on free-roaming grasslands and forests near the New Bolton Center in Pennsylvania. They descended from a line that’s been part of McDonnell’s experimental semi-feral herd project at the university since 1994.

The scientists found that the semi-feral pony foals—which had a greater variety of forage as well as more access to other horses than the domestically raised foals—had a larger diversity of what scientists call “key groups” of hindgut bacteria. That includes Verrucomicrobia (RFP12), Ruminococcaceae, Fusobacterium spp., and Bacteroides spp. They also had more microorganisms living in their guts in general. “This suggests greater functional redundancy, stability, and digestive capacity for the gut microbiomes,” the researchers stated.

Domestically raised foals, on the other hand, had more lactic acid bacteria, which is often associated with gastrointestinal illness. It might even have a role in the development of laminitis, said Tavenner.

That increased level of lactic acid bacteria might be because the domestic foals were able to eat their dams’ concentrated feeds, she said—which they did more and more as they grew tall enough to reach the feed trays. “They would munch on it, and I would see them eat it from time to time,” Tavenner said, adding that it was never a significant part of their whole diet. Whether this could set these foals up for greater susceptibility to laminitis later in life, however, would require further study, said Tavenner.

Although the scientists compared ponies to Standardbreds, breed itself was not likely to be a factor in their results, the scientists said. An analysis of data from an ongoing equine microbiome database has shown that differences in gut microbiota between horses and ponies are minor.

Interesting Trends, but Recommendations Require Further Study

Even though the results point toward better gastrointestinal health in feral foals, due to increased diversity and fewer lactic acid bacteria, that doesn’t mean the scientists are ready to make concrete recommendations.

“There’s not much you can jump to in terms of conclusions that you would have much confidence in at this stage,” said McDonnell, adding that further research is warranted. “But it certainly is thought-provoking.”

They hope future studies will lead to documenting gut health in semi-feral horses (related to colic, laminitis, and diarrhea) compared to that of domestic horses, they said, as well as to a better understanding of the way these microbiotal communities work.