Cervical opening in relation to progesterone and oestradiol during heat in beagle bitches

The relationship between hormonal profile and cervical opening and closure was analysed during heat in seven bitches. The bitches were studied each day from the beginning of pro-oestrus until 5 days after cytological metoestrus. Vaginography was performed using a radiopaque contrast dye injected through an insemination probe and blood samples were collected daily. The opening of the cervix was observed, in pro-oestrus, 2.6 +/- 2.8 days before the LH peak. The progesterone and oestradiol values at that time were 2.0 +/- 2.4 nmol l-1 and 171.1 +/- 133.1 pmol l-1, respectively. The opening of the cervix was observed concurrent with the day of the maximal value of the oestradiol:progesterone ratio, just before the decline of oestrogen preceding the LH peak. Differences between the oestradiol:progesterone ratio the day before, the day of and the day after opening were significant. The closure of the cervix occurred 6.7 +/- 1.4 days after the LH peak and 2.6 +/- 1 days before the first sign of cytological metoestrus. The progesterone and oestradiol concentrations at that time were 68.9 +/- 15.4 nmol l-1 and 16 +/- 10.3 pmol l-1, respectively. All bitches were in cytological oestrus when the cervix closed. These data indicate that there is a relationship between hormonal profile and cervical opening and that breeding success may also be temporarily limited, not only by oestrous behaviour, but also by cervical closure. In the beagle colony studied, a blood concentration of 60 nmol progesterone l-1 would give a good indication that no success will follow artificial vaginal insemination or natural mating.