Short communication. In vitro embryo production can be modified by the previous ovarian response to a superovulatory treatment in sheep

Thirty-two ewes were used to study how the ovarian response to a superovulatory treatment determines quality of oocytes recovered from ovaries after embryo collection, and their developmental capacity after in vitro maturation (IVM) and fertilization (IVF). Ewes were superovulated, and seven days after oestrus, embryos were collected and ewes divided into three groups: (+ +), n=19, ewes responding to the treatment with embryos collected after flushing; (+ –), n=8, ewes responding, but only oocytes were found; and (– –), n=5, ewes not responding to the treatment and no embryos collected. Ovaries were recovered and oocytes collected from the three groups. A significant effect of the response to the treatment was observed for oocyte quality, so that (– –) ewes presented the higher number of oocytes per ewe (p<0.001). Total number of oocytes selected for IVM and IVF was significantly higher in the same group, in comparison with (+ +) and (+ –) (p<0.001). Group (+ –) ewes presented the lowest maturation (p<0.001), fertilization (p<0.05) and cleavage rates (p<0.001). In conclusion, the ovarian response to a superovulatory treatment determines the number and quality of the oocytes recovered 7 days after the oestrus induced by the hormonal treatment. In vitro techniques could be an important tool to increase embryo production by particular ewes when they are not able to produce a significant amount of in vivo embryos