For example, if a horse who usually eats mostly hay gets more pasture grass one day, the organisms who thrive on that particular mix of foodstuffs thrive while their counterparts decline. Most of the time, these fluxes are harmless and self-correcting.
There are many other factors that can alter the microbe levels in the gut. “Anything that changes the pH, interferes with gut motility or affects the fluid levels—all would change the balance,” says Kathleen Crandell, PhD, a nutritionist with Kentucky Equine Research. In addition to sudden changes in diet, specific events that can upset the microflora levels include the administration of oral antibiotics, dehydration, fever and ingesting feed tainted with molds or bacteria.
Even stresses, such as those associated with travel and competition, can have an effect. Going on the road tends to disrupt the horse’s routine: He may not drink as much, he may be getting different hay or grasses, his anxiety may keep him off his feed entirely for a time. Also, stress produces measurable changes in levels of hormones, body temperature, immune responses, heart rate and other functions, all of which may cause the populations of beneficial bacteria to drop.
if a probiotic is helping to keep your horse happier and healthier, there’s no reason not to keep offering it.