[1] Qingdao Agr Univ, Coll Life Sci, Qingdao 266109, Peoples R China
[2] Chinese Acad Sci, Inst Zool, State Key Lab Stem Cell & Reprod Biol, Beijing 100101, Peoples R China
[3] Qingdao Agr Univ, Shandong Univ, Coll Anim Sci & Technol, Inst Reprod Sci,Key Lab Anim Reprod & Germplasm E, Qingdao 266109, Peoples R China
[4] Univ Missouri, Dept Vet Pathobiol, Columbia, MO 65211 USA