1. Aoki M, Kimura K, Suzuki O. 2005. Predicting time of parturition from changing vaginal temperature measured by data-logging apparatus in beef cows with twin fetus. Animal Reproduction Science 86, 1-12.
2. Birgel EH Jr, Grunert E, Soares JA. 1994. The preliminary stage of labor in cattle in relation to the clinical signs of labor and the course of progesterone secretion for the prediction of the calving time. Deutsche Tierarztliche Wochenschrift 101, 355-359.
3. Burfeind O, Suthar VS, Voigtsberger R, Bonk S, Heuwieser W. 2011. Validity of prepartum changes in vaginal and rectal temperature to predict calving in dairy cows. Journal of Dairy Science 94, 5053-5061.
4. Elliott CT, Francis KS, Shortt HD, McCaurhey WJ. 1995. Determination of the concentrations of the steroids estradiol, progesterone and testosterone in bovine sera : comparison of commercial dissociation enhanced lanthanoide fluorescence immunoassay kits with conventional radio and enzyme immunoassays. Analyst 120, 1827-1830.
5. Lowman BG, Hankey MS, Scott NA, Deas DW, Hunter EA. 1981. Influence of time of feeding on time of parturition in beef cows. Veterinary Record 109, 557-559.