To inspect imported grand parent layer breeders for the exogenous ALVs’infection status. We chose 3 flocks of grand parent layer breeders and 1 parent layer breeder, the cloaca swabs and sera were collected at different ages on the 45d, 20w, 35w, 45w and 57w. They were tested for p27 antigen detection and antibody. The results indicated that the infection of the exogenous ALVs was widely spread. For the three inspected grand parent layer breeders: the positive rates of p27 antigen vary considerably ...