Chichlowski, M.; Croom, J.; McBride, B.; Havenstein, G.; Koci, M. Metabolic and Physiological Impact of Probiotics or Direct-Fed-Microbials on Poultry: A Brief Review of Current Knowledge. Int. J. Poult. Sci. 2007, 6 (10), 694–704. https://doi.org/10.3923/ijps.2007.694.704.