Fig. 9

Experimental design. Animals received three weeks of treatment lead in, where animals only received kefir or milk supplementation, after which they were assessed for their behavioural phenotype. Treatment groups consisted of (1) no gavage control, (2) milk gavage control, (3) kefir gavage–Fr1, and (4) kefir gavage–UK4 (n = 12/group). The order of behavioural tests was as following: week 4: marble burying test (MB), 3-chamber social interaction test (3CT) and elevated plus maze (EPM); week 5: open-field test (OF) and tail suspension test (TST); week 6: saccharin preference test (SPT); week 7: female urine sniffing test (FUST); week 8: stress-induced hyperthermia test (SIH); week 9: intestinal motility test (IM) and faecal water content assessment (FWC): week 9–12: appetitive Y-maze; week 13: fear conditioning; week 14: forced swim test; week 15: euthanasia. Postmortem, ileal, caecal and faecal microbiota composition and function were investigated by shotgun sequencing and faecal metabolomics. Host immunity was assessed using flow cytometry and by quantification of cytokines. Finally, ileum and colonic serotonergic levels were quantified by high-performance liquid chromatography (HPLC)