A microbiome is a microbial community (bacteria, fungi, viruses and other tiny things) occupying a discrete habitat, such as the gastrointestinal (GI) tract of cats. We are just beginning to explore the roles played by bacteria and other microbes in maintaining the health of domestic cats (e.g., Inness et al. 2007, Janeczko et al. 2008, Suchodolski 2011). The GI tract of domestic cats supports a diverse bacterial community that directly influences cat health and nutrition (Simpson 1998, Jergens 2002, Guilford and Matz 2003, Weese et al. 2004). The feline duodenum (the part of the gut that the stomach empties into) harbors up to 100 million cells per gram of poop, and is dominated by bacteria that live in environments with low levels of oxygen (e.g., Johnston et al. 1993, Papasouliotis et al. 1998, Johnston et al. 2001).