Vaginal temperatures (VT) of crossbred (Japanese Black crossed Holstein-Friesian) beef cows (n = 31) were measured by a data-logging apparatus to obtain serial data from days 0 to 6 before parturition. For both single and twin pregnancies, no significant differences were observed in VT during days 3-6 before parturition. Maternal VT was not affected by maternal weight just after parturition, parity, fetal sex, or total fetal litter weight. Average of twin litter weights for two males (MM) and two females (FF) had the strong positive correlations (r = 0.84; P < 0.05) with maternal VT, whereas twin weights of mixed-gender twins (FM) did not correlate with maternal VT (r = -0.26; P = 0.61). Maternal temperature decreased as weights of the female fetus of FM twins became heavier (r = -0.82; P < 0.05). In contrast, maternal VT of FF and MM twins increased as twin weights increased. We defined when the VT began to decrease before parturition by two different methods. One was the ''same hours method'' where differences in VT between a particular time of day and the corresponding time of the preceding day were compared when the VT was consistently >=0.3 or >=0.5 o C for more than 3h. The second method was the ''maximum-minimum method'' where decreased in the maximum or the minimum values of the day over >=0.3 and >=0.5 o C were compared to values of preceding day. Onset of decreased VT before expulsion was not different between singletons and twins. In an attempt to define the critical condition in predicting parturition, we estimated assumable predicting probability using the 31 cows that were collected VT. When the parturition occurred within 60h in the ''same hours method'' and 72h since VT was >=0.3 o C and in the ''maximum-minimum method'', the assumable probability was 100%. In verification experiment under these condition, the ''same hours method'' had a higher probability of predicting the time of parturition than the ''maximum-minimum method'', and it was possible to detect the onset of decreased VT at the correct time by the minutes. We concluded that ''same hours method'' was useful for predicting parturition time in cattle with single and twin pregnancies by the serial measurement of vaginal temperature.
