ADVERTISEMENT When horses haven’t eaten for at least 10 hours, the numbers of bacteria and bacterial species in their digestive system drop significantly. Fortunately, though, healthy horses can get that microbiotal richness back within a day of eating normally. Even so, owners, veterinarians, and researchers alike need to be aware of the kinds of changes that happen in horses’ guts when they’re fasted, said Louise Southwood, BSc (Vet), Dipl. ACVS, ACVECC, a professor in emergency medicine and critical care at the University of Pennsylvania’s School of Veterinary Medicine, in Kennett Square. “Withholding food for a day definitely changes the microbiota, but it’s important to keep in mind that this is very reversible,” Southwood said. “Within 24 hours (after fasting ends), it can come back to normal.”