library_construction_protocol: In this experiment, the two factors (ME and CP) trial design was adopted, 480 18-day-old Jingdian Pekin ducks were randomly divided into 6 groups with 8 replicates, 10 ducks per replicate, respectively. The crude protein levels were 16.5% and 17.5%, and three metabolizable energy levels were 11.92 MJ/kg, 12.34 MJ/kg and 12.118 MJ/kg.