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  • Title: Period of dominance of the ovulatory follicle influences embryo quality in lactating dairy cows.
    Author: Cerri RL, Rutigliano HM, Chebel RC, Santos JE.
    Journal: Reproduction; 2009 May; 137(5):813-23. PubMed ID: 19204087.
    Abstract:
    Length of dominance of the ovulatory follicle and exposure to oestradiol (OE(2)) during proestrus can affect fertility. Lactating cows had their oestrous cycle pre-synchronized and were subjected to one of the four synchronization treatments. Cows in the oestrus detection (OD) treatment received GnRH on day 6 of the oestrous cycle, PGF(2alpha) 7 days later, and were inseminated at detected oestrus. The remaining cows were subjected to the Ovsynch (OVS) protocol (day 0 GnRH, day 7 PGF(2alpha), day 9 GnRH, and timed artificial insemination (AI) 12 h later) starting on day 3 (OVS3) or day 6 (OVS6 and OVS6E) of the oestrous cycle. Cows in the OVS6E treatment received an injection of 0.5 mg oestradiol cypionate 36 h before AI. Ovaries were examined by ultrasonography and blood was sampled for progesterone and OE(2) concentrations. Uteri were flushed 6 days after AI and recovered embryos-oocytes evaluated. Diameter of the ovulatory follicle at AI differed (P<0.01) among treatments, and it was the largest for OVS3 cows, which also had extended (P<0.01) length of follicular dominance. During proestrus, OD and OVS6E cows had increased (P<0.01) OE(2) concentrations. Fertilization was not altered by treatments, and maximum fertilization was achieved when the number of accessory spermatozoa was >7. Proportions of viable embryos in relation to embryos and embryos-oocytes recovered were smaller for OVS3 cows (P<0.01) than the other treatments, and embryos from OVS3 cows also had fewer (P<0.01) blastomeres and tended (P=0.09) to have a lower proportion of live blastomeres. Extending the period of follicle dominance did not alter fertilization but reduced (P<0.001) embryo quality. Embryo quality was compromised even when the dominance of the ovulatory follicle was extended by only 1.5 days.
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