2Schofield S A, Phillips C J, Owens A R. Variation in milk producuon, activity rate and electrical impedance of cervical mucus over the oestrus period of dairy cows[J].Atfim Reprod, 1991,24:231 - 248.
3Redden K D, Kennedy A D, Ingans J R.Detection of oestms by radiotelemetric monitoring of vaginal and ear skin temperature and pedometer measurements of activity[J]. Dairy Sci,1993,76: 713-721.
4Geers R, Puers B, Goedseels V. Electronic Identification, Monitoring and Tracking of Animals[M]. CAB International, Wallingford, NY, 1997.