Oleuropein (OLE), as the main effective active component in olive leaves, is a natural cyclic ether terpene polyphenolic compound found in plants of the genus Olea. It has antioxidant, anti-inflammatory and anti-apoptotic properties, and can reduce damage caused by reactive oxygen species. These characteristics indicate that it can enhance the maturation rate of oocytes and the developmental capacity of embryos—two key indicators in animal breeding. This study evaluated the effects of OLE on the in vitro maturation and early embryonic development of sheep oocytes. 20 μM OLE has the best promoting effect on the maturation rate of oocytes, and 30 μM OLE has the best increasing effect on the blastocyst rate. Compared with the control group, glutathione (GSH) level and mitochondrial membrane potential (MMP) level were significantly increased, ROS level was significantly decreased, the expression of antioxidant genes SOD1 and GPX3 was significantly elevated, and the expression of anti-apoptotic gene BCL2 was significantly elevated in the experimental group. In addition, during the in vitro development stage of early embryos, the expression level of the embryo development-related gene OCT4 significantly increased. The study has shown that OLE can effectively alleviate oxidative stress during in vitro culture, increase oocyte maturation rate and promote embryo development.

Natural pigment lycopene (LYC), a carotenoid, possesses antioxidant, anti-apoptotic, anticancer, and immunoenhancing properties. During in vitro culture, this substance protects oocytes and early embryos from damage caused by reactive oxygen species (ROS), thereby enhancing the in vitro maturation (IVM) rate of oocytes and the developmental competence of early embryos. This study aimed to investigate the effects of supplementing different concentrations of LYC (0, 5, 10, and 15 μM) during in vitro culture of sheep oocytes and early embryos on their developmental competence. In contrast to the control group, the 5 μM LYC treatment group displayed a marked increase in the first polar body extrusion rate and the extent of cumulus cell expansion, as well as a significantly higher proportion of normal spindle assembly in sheep oocytes, but 15 μM LYC appeared to negatively affect oocyte maturation. Relative to all other experimental groups, the 5 μM LYC treatment group displayed significantly elevated rates of cleavage and blastocyst rate during early in vitro embryonic development. The levels of ROS in mature oocytes and early embryos were significantly decreased, whereas the GSH level was significantly elevated. Furthermore, LYC treatment significantly enhanced mitochondrial activity and markedly elevated the mitochondrial membrane potential (MMP) in mature oocytes and early embryos. Moreover, the total cell number of blastocysts was significantly increased. Moreover, in early embryos, the transcript levels of genes associated with both oxidative stress and apoptosis were favorably regulated. In conclusion, LYC supplementation boosted the rates of oocyte maturation and blastocyst formation in sheep, while elevating the developmental capacity of early embryos.