The present study was designed to develop a model in piglets that allows the investigation of the effects of postnatal association with a simple or a complex microbiota on gut health and development. Thirty piglets from 2 sows were obtained by caesarean delivery (day 0) and were equally divided over 2 treatment groups housed in separate clean, nonsterile rooms. All piglets received orally a simple microbiota consisting of Lactobacillus amylovorus, Clostridium glycolicum, and Parabacteroides spp. on days 1, 2, and 3 after birth. On day 3 and 4 the piglets received either a complex microbiota by providing them with a fecal inoculant of an adult sow [complex association (CA)] or a placebo inoculant [simple association (SA)]. Fecal microbiota composition, as determined by denaturing gradient gel electrophoresis and by pig intestinal tract chip (PITChip) analysis of 16S rRNA genes (days 3, 5, 7, 14, and 28), was less diverse in the SA group compared to the CA group. A difference in fecal microbiota composition between treatments persisted until the end of the study. It was concluded that the composition of microbiota in feces of cesarean delivery-derived piglets is influenced by bacterial association in the first days after birth. Differences in fecal microbiota composition between piglets exposed to a simple or complex inoculum at early age persisted for at least 3 wk.