design: Total RNA was extracted using the RNAeasy Mini Kit, following the manufacturers instructions, and total concentration was determined using a Qubit RNA BR kit in a Qubit 2.0 Fluorometer. RNA quality was assessed with a 2100 Bioanalyzer; all the samples had an RNA Integrity Number (RIN) value > 7. Equal amounts of RNA of three different chickens of the same gender from the same experimental group and per slaughter age were pooled together; a total of four RNA pools (i.e. replicates, two per gender) for each of the three diets per slaughter age were obtained. Therefore, RNA-seq data were representative of a total of 72 animals (12 per group). Twenty-four tagged RNA-seq libraries were prepared using the Illumina TruSeq Stranded mRNA kit and sequenced on an Illumina platform at the NGS Sequencing Core (Padova, Italy) following a 100 bp paired-end approach.