Schematic representation of the experimental design used in this study. Samples of the jejunum (○), ileum (□) and colon (△) were collected from each animal at different time points (0, 1, 2 and 6 dpi). Open symbols mean non-infected pigs; filled symbols mean S. typhimurium infected pigs (a). Total RNA was extracted from all 48 intestinal samples. RNA isolated from the same intestinal segment collected from four pigs in each time point was pooled for the subsequent quantitative PCR analysis (b).