The objective of this research was to evaluate DFM strain efficacy and modes of action utilizing in vitro fermentation models. Three experiments were conducted; the first focused on selecting a DFM strain for inhibition of Salmonella Typhimurium utilizing co-culture and mixed microorganism in vitro, which demonstrated L. lactis has antagonistic activity against Salmonella Typhimurium and potentially inhibits in the lower gastrointestinal tract. The second study compared DFM effects on fermentation parameters in rumen and fecal mixed microorganism in vitro models and found while DFM increased total gas production in fecal in vitro, there were no clear differences in DFM treatment affecting fermentation patterns. The third study evaluated DFM effects on rumen and fecal microbiome in vitro analyzing alpha diversity indices and genera abundances and found many differences caused by DFM in which L. lactis showed the most promise for further work in vivo.