Descent of Ova and Embryos in Cows Superovulated with Serum Gonadotropin

Veterinarni Medicina 37, 1992, 353-364

The descent and localization of eggs and embryos in individual segments of the reproductive tract of superovulated cows were studied in this work. For the induction of superovulation, serum gonadotropin (PMSG, Ivanovice in Hana) at a dose of 2500-3500 I.U. was used, in combination with 0.5 mg of Cloprostenol (Oestrophan, Spofa), administered 48 hours after gonadotropin treatment. The start of superovulation fell on days 9 to 12 of the sexual cycle and was conditioned by the presence of the corpus luteum (CL). After the onset of the heat, 2-3 inseminations were carried out using fresh semen. Donor cows were slaughtered 3, 4, 5, 6, and 7 days after the second insemination and isolated reproductive organs (Fig. 1) were divided into five segments (two on oviducts and three on uterine horns) by the applied ligature. In laboratory conditions superovulation response was determined accurately, the volume of ovaries was assessed according to water displacement and the segments of oviducts and uterus were rinsed with TCM 199 or PBS supplemented with FCS. 3, 4, 5, 6, and 7 days after insemination (Tab. I). 18.1 (+/- 3.55), 12.4 (+/- 0.91), 19.2 (+/- 2.86), 20 and 23 (+/- 2.44) CL on average were recorded, which corresponded to the ovulation of 64, 50, 56, 71 and 72 percent of stimulated follicles (Fig. 2). Within 3 to 7 days after insemination nearly triple enlargement of ovaries was also observed (Tab. I, Fig. 3). During the lavage of individual segments of the tubular reproductive tract, 38 per cent of eggs and embryos were detected in the uterus as early as 3 days after insemination (Tab. II). Unfertilized eggs and degenerated embryos were found in the 2nd and 3rd uterine segment, embryos at the stage of 8-16 blastomeres were localized in the 1st and 2nd segment of the uterus. Four days after insemination (Tab. III), about 64 per cent of eggs and embryos at the stage up to 16 blastomeres were found in the uterus, but embryos up to 32 blastomeres were still flushed out of the oviduct. On day 5 after insemination, 92 per cent of eggs and embryos were released into the uterus, being localized mostly in the cranial and medial part of the uterus (Tab. IV). 7.5 per cent of recovered eggs and embryos at the stage of early or compacted morulae were still detected in the oviducts. In 6 days after insemination (Tab. V), all eggs descended to the uterus, but on day 7 after insemination still 1.6 per cent of embryos at the stage of 16 blastomeres were flushed out of the oviduct. Sixty-five per cent of detected eggs and embryos were found in the anterior, 23 per cent in the medial, and nearly 10 per cent in the caudal third of the uterus. It means that at the time of current collection of embryos on day 7 of the superovulation cycle, more than 11 per cent of eggs and embryos are inaccessible by flushing. Detection of free zonae pellucidae, appearing in the flush already from the 3rd day after insemination, was also remarkable. Free blastocysts, however, were not recorded at that time. Findings of relatively advanced developmental stages of embryos and free zonae pellucidae in the uterus as early as 3 days after insemination may partly be related to the very early ovulation of developed (dominant) follicles induced by a luteinizing fraction of PMSG, but first of all they are due to accelerated descent of eggs and embryos conditioned by changes in the ovarian hormonal situation

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