Data sourcesThis dataset was constructed using the samples of the MetaChick project (phase 1) corresponding to the cecal content of 340 animals. Sequencing data and associated metadata have been submitted to INSDC (bioproject: PRJEB38174). Sequencing data QC and metagenomic assemblyFirst, sequencing adapters removal and read trimming was performed with fastxtend. Reads mapped on the host genome (GRCg7b GCA_016699485.1) with bowtie2 were removed with samtools. Finally, metagenomic assembly was performed with metaSPAdes v3.14.1. Contigs of less than 1500 bp were removed. MAGs recoveryMAGs were generated with MetaBAT 2 (multi-coverage mode) and MAGs quality was assessed with CheckM. MAGs with completeness 5% or N50 < 8Kb were discarded. Pairwise Average Nucleotide Identity (ANI) was computed for all recovered MAGs with fastANI and dereplication at species level (ANI cutoff = 95%). Non-redundant gene catalogGenes were predicted on all contigs from metagenomic assemblies with Prodigal (parameters : -m -p meta). Genes were pooled and clustered with cd-hit-est (parameters -c 0.95 -aS 0.90 -G 0 -d 0 -M 0 -T 0) by choosing those from the longest contigs as representatives. MSPs recoveryA raw gene abundance table (13,6M genes quantified in 340 samples) was generated with meteorMeteor. Then, co-abundant genes were binned in Metagenomic Species Pan-genomes (MSPs, i.e. gene clusters that likely belong to the same microbial species) using MSPminer. MAGs and MSPs taxonomic annotationDereplicated MAGs were annotated with GTDB-Tk based on GTDB r214. Then, MAGs taxonomic annotation was propagated to the corresponding MSPs. Construction of the phylogenetic tree39 universal phylogenetic markers genes were extracted from the dereplicated MAGs with fetchMGs. Then, the markers were separately aligned with MUSCLE. The 40 alignments were merged and trimmed with trimAl (parameters: -automated1). Finally, the phylogenetic tree was computed with FastTreeMP (parameters: -gamma -pseudo -spr -mlacc 3 -slownni).