3GATIUS F I., SANTOLARIA P, YAN1Z J, et al. Factors af fecting pregnancy loss from gestation day 38 to 90 in lactating dairy cows from a single herd[J]. Anim Reprod Sci,2002(57) : 1251-1261.
4MARSHALL J F,BARRETT D C, LOGUE D N, et al. Cattle praetice[M]. 6th Edition.北京:中国农业大学出版社,2003:151-152.