Effects of insemination–ovulation interval on fertilization rates and embryo characteristics in dairy cattle

The objective of this study was to examine effects of the interval between insemination and ovulation on fertilization and embryo characteristics (quality scored as good, fair, poor and degenerate; morphology; number of cell cycles and accessory sperm number) in dairy cattle. Time of ovulation was assessed by ultrasonography (every 4 h). Cows were artificially inseminated once between 36 h before ovulation and 12 h after ovulation. In total 122 oocytes/embryos were recovered 7 d after ovulation. Insemination–ovulation interval (12 h-intervals) affected fertilization and the percentages of good embryos. Fertilization rates were higher when AI was performed between 36–24 and 24–12 h before ovulation (85% and 82%) compared to AI after ovulation (56%). AI between 24 and 12 h before ovulation resulted in higher percentages of good embryos (68%) compared to AI after ovulation (6%). Insemination–ovulation interval had no effect on number of accessory sperm cells and number of cell cycles when corrected for embryo quality. This study showed that the insemination–ovulation interval with a high probability of fertilization is quite long (from 36 to 12 h before ovulation). However, the insemination–ovulation interval in which this fertilized oocyte has a high probability of developing into a good embryo is shorter (24–12 h before ovulation).