4Kinsel M L,Marsh W F,Ruegg P I,et al.Risk factor of twinning in dairy cows[J].Dairy Sci,1998,81(4):989-993.
5Herr C M,Reed K C.Micromanipulation of bovine embryos for sex determination[J].Theriogenology,1991,35(1):45-54.
6Parkinson T J,Smith K C,Long S E,et al.Interrelationships among gonadotrophins,reproductive steroids and inhibin in freemartin ewes[J].Reproduction,2001,122(3):397-409
7Dadula A M.The freemartin syndrome:an update[J].Animal Reproduction Science,2005,87:93-109.
