CERVICAL OPENING IN RELATION TO PROGESTERONE AND ESTRADIOL DURING HEAT IN BEAGLE BITCHES

The relationship between hormonal profile and cervical opening and clo sure was analysed during heat in seven bitches. The bitches were studi ed each day from the beginning of pro-oestrus until 5 days after cytol ogical metoestrus. Vaginography was performed using a radiopaque contr ast dye injected through an insemination probe and blood samples were collected daily. The opening of the cervix was observed, in pro-oestru s, 2.6 +/- 2.8 days before the LH peak. The progesterone and oestradio l 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 concu rrent with the day of the maximal value of the oestradiol:progesterone ratio, just before the decline of oestrogen preceding the LH peak. Di fferences between the oestradiol:progesterone ratio the day before, th e day of and the day after opening were significant. The closure of th e cervix occurred 6.7 +/- 1.4 days after the LH peak and 2.6 +/- 1 day s before the first sign of cytological metoestrus. The progesterone an d 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 cytolog ical 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 oestrou s behaviour, but also by cervical closure. In the beagle colony studie d, a blood concentration of 60 nmol progesterone l(-1) would give a go od indication that no success will follow artificial vaginal inseminat ion or natural mating.