design: Male C57BL/6 mice were randomly divided into six groups (n=10 per group): Vehicle, clindamycin (Clin), native bovine lactoferrin (nLf), nLf + clindamycin (nLf_Clin), iron-saturated bovine lactoferrin (sLf) and sLf + clindamycin (sLf_Clin).  Vehicle group received 200 uL of saline solution orally for 10 days. Clindamycin group was gavaged for 10 days with saline and on day 4 received a single IP injection of 200 g of clindamycin diluted in 200 l of saline. nLf and sLf  groups were gavaged for 10 days with 35 mg of nLf or sLf respectively, diluted in 200 l of saline. The groups nLf_Clin and sLf_Clin were gavaged with nLf or sLf and on day 4 received an  IP injection of clindamycin. Following each treatment, fecal samples were collected directly in soil grinding sterile SK38 2 ml tubes, and immediately frozen at -80C to fix bacterial growth and preserve DNA content. Bacterial DNA was extracted from faecal samples using the QIAamp Fast DNA Stool Mini Kit (Qiagen, Hilden, Germany).16S rRNA gene of V4 region was amplified using specific primer (515F-806R) (Caporaso et al., 2011) with a barcode. All PCR reactions were carried out with Phusion High-Fidelity PCR Master Mix (New England Biolabs, USA). Sequencing libraries were generated using NEBNext Ultra DNA Library Pre Kit for Illumina. Later, the library was sequenced on an Illumina MiSeq platform and 250 bp paired-end reads were generated.