2.4. Fecal Sample Collection
Two types of fecal samples were prepared: fresh fecal samples were collected before intake and at 1 month of age, and fecal samples with the preservative solution, guanidine thiocyanate solution, were collected before intake, 1 week after intervention, and at 1 month and 3 months of age. Both fecal samples were collected from infants’ diapers in each stool collection tube (Techno Suruga Laboratory Co., Ltd., Shizuoka, Japan). Fresh fecal samples were collected within 24 h of the hospital visit and were stored in a foamed styrene box with cooling agent at home, whereas fecal samples with the preservative solution were stored at room temperature at home. Both samples taken at home were transferred to the hospital and stored in −20 °C freezers. After being transported to the laboratory with dry ice, they were stored at −80 °C before DNA extraction. Fresh fecal samples were used for the analysis of real-time PCR, pH, SCFAs, and biomarkers, whereas fecal samples with the preservative solution were used for 16S rRNA gene sequencing. All participant samples were blinded to the process and analysis.