and had free access to feed and water. The house was automatically ventilated to maintain an ambient tempera- ture between 20 and 28°C, with a photoperiod of 16 h light/d at 15 lx. These conditions induced some hens to exhibit broodiness, and 3 to 5 eggs were allowed to remain in each nest to promote the broody condition. The 4 wk after transferring to the windowless house was regarded as a transition period, and broody traits were not recorded during this period.
White Leghorns (n = 72), a maternal line of Hy-Line brown egg layers (n = 93), a maternal line of Avian broiler breeders (n = 20), and Chinese local breeds including Shou-guang (71), Beijing-you (n = 48), and Silkie (n = 222) were screened for allelic frequencies of the PRL gene. These breeds or lines, excluding Shou-guang and Beijing- you, were also screened for allelic frequencies of the PRLR gene. The White Leghorns have a long history of selection against broodiness, whereas this behavior is still common in Chinese local breeds.