Probiotics, or direct fed microbials, are an entire class of live microorganisms with a very complicated but intriguing story (Krestel-Rickert and Kisic, 2003). These microbes aren't necessary to the diet for palatability or processing purposes, nor do they contribute directly to the nutrition of the animal. Rather, they are a natural complement to prebiotic soluble fibers like inulin, beet pulp or soy hulls, which are intended to support the health of the lower gastrointestinal (GI) tract.
Instead of providing substrate to the indigenous flora in the colon, probiotics represent the adding of beneficial microorganisms to the colon. The pay-off can be the prevention and treatment of such diseases as diarrhea (Sauter et al., 2006). However, describing their benefit to the animal can border on a medical claim rather than nutritional fortification. This can be problematic when it comes to crafting a marketing message necessary to justify their addition and cost in commercial petfood. Unfortunately, like a vaccination they don't offer much in the way of outward or observable results. Issues also extend to determining which probiotic organisms to use and how to get them into the animal.
