Interestingly, at day 176, we found a significant difference in microbiota diversity and composition of the pigs only treated with the antibiotic in comparison to the other AdipoRon hydrochloride treatment groups. Since all three groups were exposed to similar environmental conditions, the differences in microbiota diversity and composition observed at day 176 after birth can only be explained by group specific intrinsic animal factors. One could argue that the intestinal immune cells of the T2 animals were programmed differently from the T1 and T3 animals, due to the antibiotic treatment at day 4 after birth. Differences in immune programming may then lead to differences in 3-Deazaneplanocin A hydrochloride immunologic and microbial homeostasis. Why these differences in microbial homeostasis cannot be observed at day 55 is not clear, but it could be explained by the fact that at day 55 the composition and diversity of the gut microbiota have not been stabilized yet due to the relative proximity to the weaning period, which occurred around day 26 in this study. The weaning period is known to cause a large shift in the composition and diversity of gut microbiota. In this short time-period of weaning the gut ecosystem must progress from a rather simple stable equilibrium to a more complex stable equilibrium. Another explanation could be that in the life history between day 55 and 176 the T2 animals have reacted differently to an unknown external factor because the intestinal immune cells of the T2 animals were programmed differently from T1 and T3 animals, due to the antibiotic treatment at day 4 after birth. Because the clinical data from this study did not suggest any signs of an infection, it is more likely due to the differences in immune programming that lead to differences in maintenance of immunologic and microbial homeostasis upon exposure to that presumed external factor. However, the results of more detailed analysis of the microbiota data are more supportive for our first explanation/hypothesis. When zooming in on the differences in microbial composition and diversity by the use of univariate analysis, we observed that two microbial groups differed significantly when comparing antibiotic treated pigs with antibiotic and stress treated pigs, namely Coprococcus eutactus et rel. and uncultured Prevotella. At day 176 a larger number of significant differences in the relative abundance of genus-level microbial groups was found. It is striking that in T2 pigs almost in all cases the average relative contribution of these groups was lower compared to that found in T1 or T3 pigs. For example the following microbial groups were lower in T2, Streptococcus suis et rel., uncultured Prevotella, Fusobacterium et rel., Bacteroides distasonis et rel., and Prevotella melaninogenica et rel.. It has previously been shown that Streptococcus suis, a potential pathogen, is more abundant in the pig intestine directly after weaning.