The first strand cDNA was synthesized, followed by second strand cDNA synthesis. cDNA was then transcribed and labeled with T7 RNA Polymerase and cyanine 3-CTP. After purified by RNeasy Mini Kit (Qiagen, Germany), the labeled cRNA was fragmented to segments using fragmentation buffer at 60°C for 30 min. Then, the fragmented cRNA were then hybridized to Agilent custom 4x44k chips, representing 15008 sheep genes, provided by Beijing Protein Innovation