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PubMed2001

Determination of the role of cervical closure in fertility regulation after mating or artificial insemination in beagle bitches.

In the present study, the pregnancy rate after one insemination with fresh semen performed at the optimum period of fertilization (control) was compared with the pregnancy rate after insemination by either vaginal deposition of semen or transcervical uterine insemination at 24, 48 or 72 h after closure of the cervix (n = 5 bitches per time period and group). In the group of bitches inseminated into the uterus, 2 ml of a fresh pool of semen from four male dogs was deposited transcervically or by laparoscopy into the uterus, whereas in the vaginally inseminated animals, 2 ml fresh semen was extended with 4 ml prostatic fluid. The study was performed over 5 years; some bitches were used twice during two consecutive oestrous cycles. Closure of the cervix was determined once a day by retrograde vaginogram using a radiopaque contrast dye. Closure of the cervix occurred 6.9 +/- 1.1 days (mean +/- SD) after the LH peak and 1.5 +/- 0.9 days before the first day of cytological metoestrus. The hormone values at the time of closure were 81.2 +/- 12.3 nmol progesterone l-1 and 28.4 +/- 23.2 pmol oestradiol l-1; there were no differences between groups. Of the bitches inseminated before closure of the cervix, five and four bitches became pregnant after uterine and vaginal insemination, respectively. Of the bitches inseminated into the vagina 24, 48 or 72 h after cervical closure, none became pregnant, whereas three, three and one bitches became pregnant after insemination directly into the uterus at 24, 48 or 72 h after cervical closure, respectively. The mean litter size was 3.9 +/- 1.4 pups among all pregnant animals and there were no significant differences between groups. The results of the present study indicate that mature canine oocytes may remain fertile for > 200 h after ovulation, rather than for 48-60 h as was previously believed, and that cervical closure may be a limiting factor for reproductive success after natural mating.

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