Housing influences tissue cytokine levels and the fecal bacterial community structure in rats

Immune measures and the fecal bacterial community were examined in female Biobreeding rats housed in wire bottom cages (wire) or in solid bottom cages containing hardwood chips (bedding). Housing did not affect food intake, weight gain, fecal output or fibre content, serum liver enzymes, or spleen and mesenteric lymph node immune cell populations. Bedding-housed rat feces were enriched in phylotypes aligning within the phylum Firmicutes (families Lactobacillaceae and Erysipelotrichaceae) and had a 2-fold lower content of phylotypes aligning within the phylum Bacteroidetes. Feces from bedding-housed rats also contained significantly more acetic acid and less propionic, isobutyric, valeric and isovaleric acids than those housed on wire. Bedding-housed rats had significantly higher splenic concentrations of interleukin-4 (P < 0.001). These results demonstrate that bedding can indirectly influence systemic and mucosal immune measures, potentially adding additional complexities and confounding results to nutrition studies investigating the health effects of dietary fibres.