The bacterial populations present in the porcine gut play an important role in pig health. A number of factors may influence these populations including diet, medication and environment. To identify what effects rearing environments have on the gut microbiota, this study compares the numbers of four common groups of gut organisms – enterococci, Bacteroides spp., lactobacilli and coliforms – in faecal samples taken from pigs reared either indoors or outdoors. The presence of three zoonotic bacteria – Campylobacter jejuni, Clostridium difficile, and Verocytotoxigenic Escherichia coli O157 -was also assessed to determine whether rearing environment might influence the threat of zoonotic infections.