DNA was extracted from the fecal material (approx. 100mg) using the automated assisted method based on magnetic beads (Maxwell RSC Instrument coupled with Maxwell RSC Pure Food GMO and authentication kit, Promega, Spain) following the manufacturers instructions with previous treatments to improve the DNA extraction. DNA libraries were constructed with the amplification of the V3-V4 variable region of the 16S rRNA gene. A multiplexing step was conducted by the NextEra XT Index Kit (FC-131-2001) (Illumina, San Diego, CA, USA) and DNA quality of the library PCR product was measured by a Bioanalyzer DNA 1000 chip (Agilent Technologies, Santa Clara, CA, USA) to verify the size; the expected size on a Bioanalyzer trace is~550bp. The libraries were sequenced using was a 2300bp paired-end run on a Illumina platform (FISABIO sequencing service, Valencia, Spain) according to manufacturer instructions. Controls during DNA extraction and PCR amplification were also included and sequenced.