Probiotics have been studied for more than a century, and their use is now common for food animals, such as cattle. For the past decade or so, veterinarians have been administering them to horses, too, to aid recovery from serious intestinal illnesses. Described in academia during the 1960s and ’70s as any organism or substance that benefited the intestinal microbial balance, the generally accepted meaning today is “a live microbial supplement which beneficially affects the host animal by improving its intestinal microbial balance.”
“The main goal of administering probiotics is to manipulate the normal intestinal flora in such a way that is beneficial to the health of the horse,” Swyers says. “With that said, researchers are looking for ways that we can use probiotics to improve the digestibility of feedstuffs, reduce the incidence of digestive upsets that could lead to colic or diarrhea, and act as a natural alternative to administering antibiotics, just to name a few areas of interest.”
The inside of a horse’s gut is home to colonies of bacteria, protozoa and fungi, often referred to en masse as the intestinal flora or microflora. “It has been estimated that there are approximately five billion organisms per gram of digestive fluid in the mammalian digestive tract,” Swyers says.
These tiny organisms are engaged in the usual activities of life: consuming one set of substances, excreting another and reproducing. Together they create a complex, symbiotic web. The excretions, called metabolites, produced by one organism may feed another, which in turn produces a third that may be a nutrient necessary to the horse’s life. For example, the complex molecules in starches and cellulose cannot be directly absorbed by the horse’s intestine—they must first be broken down by the flora into components that he can use.