The correlation between the cytology of the vaginal smear and the time of ovulation in the bitch

The correlation between the vaginal smear and the calculated time of ovulation was studied in 22 bitches, during a total of 24 heat periods. Blood plasma was analysed for levels of oestradiol and progesterone from 6 days before to 6 days after the day of maximum keratinization of the vaginal smear. In all 24 heat periods (100 per cent) maximum keratinization of the vaginal epithelial cells was observed at least 3 days after peak oestradiol levels and in 17 of the heat periods (70.8 per cent) maximum keratinization was seen when the peripheral plasma level of progesterone had increased to >5.44 ± 0.93 ng/ml, which has been calculated as the ovulatory level.