The present invention provides novel strains of probiotics for use in the gastrointestinal tract of a pet. The probiotics of the present invention are capable of fermenting starch to produce lactic acid and/or hydrogen peroxide anti-pathogenic metabolites. The present invention also provides a novel method for identifying the effectiveness of a pet probiotic in vitro. The method simulates the introduction of a probiotic candidate in the gastrointestinal tract of a pet and measures the anti-pathogenic effectiveness of the probiotic.