## 4 Discussion  
This study focused on the evolution of pigs' fecal microbiota composition from post-weaning to finishing at both bacteria and ecosystem levels. In our experiment, the diversity increased when  
Figure 4: Number of female pigs switching between enterotypes (FE1 and FE2) during the finishing stage (between 99 and 154 d of age). Figure 3: Number of pigs switching between enterotypes according to (**a**) the sex type (castrated males and females) or (**b**) the exposition to mycotoxins via the diet. Enterotypes from the post-weaning stage are represented by PWE1 and PWE2 and from the finishing stage by FE1 and FE2. Figure (**a**) was based on castrated males and females from the second replicate only. In Figure (**b**), based on castrated and females from both replicates, the CC, DC, CD, and DD experimental groups correspond to pigs fed with a control finisher diet, exposed to a DON-contaminated diet between 113 d and 119 d, between 134 d et 140 d, and between both 113 d and 119 d and 134 d and 140 d of age, respectively. the pigs were aging, as previously observed [20; 21; 22]. At the phylum level, the Firmicutes' relative abundance increased especially between post-weaning and finishing periods [22] and remained stable during the late-stages [23]. In accordance with [PERSON] et al. [23], the relative abundance of Spirochaetes increased during the finishing period. However, our results on the relative abundances of Spirochaetes, Actinobacteria and Bacteroidetes differed from those of [PERSON] et al. [22] where Actinobacteria gradually replaced Spirochaetes and Bacteroidetes increased as the pigs grow older. At a family level, the main changes in abundance appeared between post-weaning and finishing in accordance with previous findings [21]. Furthermore, we demonstrated that the microbiota composition kept evolving during all tested stages based on the NMDS and the relative abundance at family and genus levels in line with the results of [PERSON] et al. [24] despite previous studies demonstrating that a stabilized composition of the microbiota was reached around three months of age [22; 23]. Based on our results, the enterotype definition was age-dependent, as two enterotypes (PWE1 and PWE2) were identified at 52 days of age and another two (FE1 and FE2) were identified between 99 and 154 days. The constant evolution of the microbiota composition before three months of age [22; 23] might explain that different enterotypes can be observed at different time points. Our PWE1 and PWE2 enterotypes described at 52 days of age differed from the enterotypes previously described at 60 days of age [12]: the PEA enterotype dominated by _Ruminococcus_ and _Treponema_, and the PEB enterotype dominated by _Prevotella_ and _Mitsuokella_. Indeed, _Ruminococcus_ did not differentiate PWE1 and PWE2, while it is a major marker between PEA and PEB. Interestingly, the PWE2 enterotype partially corresponds to the PEB enterotype with greater relative abundance of _Prevotella_ and _Mitsuokella_, but the relative abundance in _Treponema_ in PWE2 pointed towards PEA. These differences in the enterotypes at post-weaning could be related to differences in the diets. However, despite differences in the diet composition and the breeds during the finishing stage, the FE1 and FE2 enterotypes observed from 119 to 152 days of age in our study were consistent with previous observations [13; 25]. Enterotypes are unstable, yet robust. Indeed, the pigs moved from an enterotype defined at 52 days of age to another one defined at 99 days of age but the pigs' affiliation to an enterotype at 99 days was not determined by its affiliation to a specific enterotype at 52 days. Similar results were described between enterotypes in the post-weaning period [11] and between weaning and finishing [13]. Furthermore, during the finishing stage, pigs' affiliation to an enterotype was not stable and they could switch enterotypes several times from 99 to 154 days.