Abrupt weaning of four-week-old pigs is associated with multiple stressors. Housing pigs in intact litters is a way to reduce the stress associated with moving and mixing of unfamiliar pigs. Furthermore, higher weaning weight may improve pigs\' robustness against postweaning stressors. In the present study, it was investigated whether: (1) A heavier pig hybrid, and (2) weaning intact litters in the farrowing pen for loose-housed sows could increase postweaning feeding behaviour and growth. Two sow hybrids (DanBred LY (DB) and Topigs Norsvin TN70 (TN)) and two weaning strategies (the litter stayed intact in the farrowing pen after removing the sow (STAY), or two litters were moved and mixed in conventional weaner pens (MOVE)) were compared in a 2 × 2 factorial design. In total, 57 litters from four batches were included in the study. The TN hybrid sows gave birth to heavier piglets but smaller litter sizes and had more functional teats than DB sows. At weaning, TN pigs were heavier than DB. The number of feed trough (FT) visits on the day before weaning was low in both hybrids. On the day after weaning, the number of FT visits was higher in MOVE compared to STAY, and in TN-STAY compared to DB-STAY. The average daily gain the first two days postweaning was negative in both hybrids and weaning strategies but more pronounced in DB than TN, and STAY tended to lose more weight than MOVE. Over the entire 28-day postweaning period, there was an interaction between hybrid and weaning strategy in that TN-STAY (392 g/d) had higher growth than both TN-MOVE (251 g/d) and DB-MOVE (283 g/d), whereas growth of DB-STAY (316 g/d) was intermediate. In addition, higher weaning weight was associated with a lower number of FT visits and greater weight loss the first two days postweaning but higher growth over the 28-day postweaning period. The results show that abrupt weaning at four weeks of age causes weight loss the first days postweaning despite being housedas intact litters, most likely due to low feed consumption. However, the combination of a heavier pig hybrid and housing intact litters in the farrowing pen postweaning resulted in a higher growth performance over the 28-day postweaning period. In conclusion, pigs that are heavier at weaning reach better growth performance in the longer term, despite having the largest acute postweaning growth depression and fewest FT visits on the day before and after weaning.

We established an infant mouse model for colonization and transmission by nonencapsulated Streptococcus pneumoniae (NESp) strains to gain important information about its virulence among children. Invasive pneumococcal diseases have decreased dramatically since the worldwide introduction of pneumococcal capsular polysaccharide vaccines. Increasing prevalence of nonvaccine serotypes, including NESp, has been highlighted as a challenge in treatment strategy, but the virulence of NESp is not well understood. Protective strategies against NESp colonization and transmission between children require particularly urgent evaluation. NESp lacks capsules, a major virulence factor of pneumococci, but can cause a variety of infections in children and older people. PspK, a specific surface protein of NESp, is a key factor in establishing nasal colonization. In our infant mouse model for colonization and transmission by NESp strains, NESp could establish stable nasal colonization at the same level as encapsulated serotype 6A in infant mice and could be transmitted between littermates. Transmission was promoted by NESp surface virulence factor PspK and influenza virus coinfection. However, PspK deletion mutants lost the ability to colonize and transmit to new hosts. Promotion of NESp transmission by influenza was due to increased susceptibility of the new hosts. PspK was a key factor not only in establishment of nasal colonization but also in transmission to new hosts. PspK may be targeted as a new candidate vaccine for NESp infection in children.

The intestinal microbiota is a fundamental factor that broadly influences physiology. Thus, studies using transgenic animals should be designed to limit the confounding effects of microbiota variation between strains. Here, we report the impact on intestinal microbiota of co-housed versus F2-generation littermates, two commonly used techniques to standardize microbiota in animal models. Our results establish that while fecal microbiota is partially normalized by extended co-housing, mucosal communities associated with the proximal colon and terminal ileum remain stable and distinct. In contrast, strain inter-crossing to generate F2 littermates allows robust microbiota standardization in fecal, colon, and ileum sampling locations. Using reciprocal inter-crosses of P1 parents, we identify dissymmetry in F2 community structures caused by maternal transmission, in particular of the Verrucomicrobiaceae. Thus, F2 littermate animals from a unidirectional P1 cross should be used as a standard method to minimize the influence of the microbiota in genotype-phenotype studies.

Several human diseases are thought to evolve due to a combination of host genetic mutations and environmental factors that include alterations in intestinal microbiota composition termed dysbiosis. Although in some cases, host genetics may shape the gut microbiota and enable it to provoke disease, experimentally disentangling cause and consequence in such host-microbe interactions requires strict control over non-genetic confounding factors. Mouse genetic studies previously proposed Nlrp6/ASC inflammasomes as innate immunity regulators of the intestinal ecosystem. In contrast, using littermate-controlled experimental setups, we recently showed that Nlrp6/ASC inflammasomes do not alter the gut microbiota composition. Our analyses indicated that maternal inheritance and long-term separate housing are non-genetic confounders that preclude the use of non-littermate mice when analyzing host genetic effects on intestinal ecology. Here, we summarize and discuss our gut microbiota analyses in inflammasome-deficient mice for illustrating the importance of littermate experimental design in studying host-microbiota interactions.

NLRP6 is a Nod-like receptor expressed in the intestinal epithelium. Previous studies reported a protective role for NLRP6 against intestinal injury and colitis-associated carcinogenesis via the regulation and establishment of a healthy microbiota. However, these results were not obtained using littermate animals, leaving the possibility that the pro-colitogenic microbiota phenotype associated with knockout (KO) mice was stochastically acquired and genotype independent. Here, we analyzed the microbiota at three intestinal locations from Nlrp6-/- and wild-type (WT) littermates, either co-caged or individually caged after weaning. Our results demonstrate that NLRP6 does not significantly influence the intestinal microbiota at homeostasis, and they support a previously reported sex-biased microbial community structure. Moreover, WT and Nlrp6-/- littermate mice displayed comparable sensitivity to dextran sulfate sodium (DSS)-induced colitis, although increased sensitivity was noted in KO females. Our results clarify the role of NLRP6 in microbiota and colitis control, and they highlight the importance of analyzing littermate animals in such studies.