Breeder eggs (53.66±0.33 g) from sixty 35-week-old Sanhuang broiler breeders (Gallus gallus; a local crossbred broiler breed), purchased from Sanhuang broiler breeding farm (Wen's group, Guangdong, China) were allocated to two groups (80 in each group) and injected into the albumen of the eggs with 0 (Control, Con) or 5.0 μg (Leptin, Lep) of recombinant murine leptin in 100 μL of phosphate-buffered saline (PBS) before incubation.