The current study describes the development of the porcine microbiota and its metabolic activities during the neonatal and weaning period. Using 16S rRNA-based approaches, we first analysed the ileal and colonic microbiota of neonatal piglets at days 2, 5 and 12 after birth. To further investigate the effect of weaning at 3 weeks of age, 19-day-old piglets (n = 64) were randomly allocated into two groups. Half of the piglets remained with their sows throughout the study, while the remaining piglets were weaned. As revealed by sequence analysis of 16S rRNA gene amplicons, the samples of 2-day-old piglets harboured a consortium of bacteria related to Escherichia coli, Shigella flexneri, Lactobacillus sobrius, Lactobacillus reuteri and Lactobacillus acidophilus. Moreover, species-specific real-time polymerase chain reaction assays unveiled that L. sobrius and L. reuteri predominated in the ileal samples of the neonatal and unweaned piglets with population levels up to 7 x 10(8) cells per gram of lumen content. Following weaning, however, these two lactobacilli were detected at significantly lower levels (< 10(3)) in the ileal samples. Furthermore, a shift in composition and metabolic activities of the predominant microbiota, and emergence of clostridia and E. coli, were encountered in the intestinal samples of the piglets after the early post-weaning period.