Heat map showing the relative abundance (> 0.001 cut-off) and prevalence (75% cut-off) of the prokaryotic OTUs in the 70 equine fecal samples analyzed. Different detection thresholds are used, providing information regarding the relative abundance of the OTUs relative to their prevalence. Taxonomic assignments of the OTUs are given to five taxonomic ranks (phylum, class, order, family and genus) where possible, followed by the OTU ID number. Where this was not possible, the non-annotated ranks were left empty (e.g. Verrucomicrobia; WCHB1–41; uncultured_bacterium;;; 3316664 has no information for the family and genus ranks). OTUs present in all animals (i.e. core) have their taxonomic assignments written in green.