Abstract:

The aim is to screen for more efficient cryopreservation schemes for bovine in vitro embryos by comparing the effects of different vitrification and programmed cryopreservation schemes. The 2-hour recovery rate, 24-hour hatching rate, and 45 day initial pregnancy rate between instrument vitrification and manual vitrification frozen bovine embryos in vitro were compared; the 2-hour recovery rate, 24-hour hatching rate, and 48-hour hatching rate of frozen bovine in vitro embryos between two programmed freezing schemes were compared; and the pregnancy rates of 45 day transplantation of fresh embryos in vitro, frozen embryos in vitro, and frozen embryos in vitro in cattle were compared. There was no significant difference in the 2-hour recovery rate (72.91%±5.52% vs.70.91%±6.75%) and 24-hour hatching rate (60.42%±6.33% vs. 58.18%±5.62%) between the instrument vitrification freezing scheme and the programmed freezing scheme for thawed embryos (P>0.05). The 24-hour hatching rate of frozen thawed embryos with sucrose scheme in programmed freezing was significantly higher than that of the freezing scheme without sucrose (44.23%±3.33% vs. 37.50%±3.58%) (P<0.05). The 45 days examination pregnancy rates of fresh bovine embryos in vitro, frozen bovine embryos in vitro, and frozen bovine embryos in vivo were 56.81%±6.27%, 45.00%±6.13%, and 49.41%±7.55%, respectively. In practical applications, there is still a certain gap in the freezing effect of bovine embryos produced in vitro compared to in vivo embryos. There is no significant difference in the effect between instrument vitrification freezing and manual vitrification freezing. The use of sucrose in the programmed freezing scheme can significantly improve the freezing effect.

Key words: in vitro embryo of cattle, vitrification, programmatization, pregnancy rate, cryopreservation