Cryopreservation of oocytes and embryos is a supplementary technique for in vivo and in vitro embryo production. In the last decade, the technique has been improved but did not achieve a satisfactory commercial level. Also, the results were variable. The pregnancy and live birth rates were 16 to 52% and 5.3 to 26.9% after implantation of vitrified embryos, respectively (from the year 1993 to 2020). In final consideration, the quality of oocytes and embryos is the most important factor to obtain better results after cryopreservation. The addition of antioxidant and lipid-depleting agents to the medium is a factor that improves cryogenic tolerance. Additionally, two-step vitrification is a reliable method for cryopreservation. Studying epigenetic effects and introducing lipidomic, transcriptomic and proteomic technologies can help improve this technology.

Summary Carvacrol (C10H14O), an efficient phenolic antioxidant substance for several cell types, may become a useful antioxidant for female germ cells and embryo culture. This study investigates the effects of carvacrol supplementation on bovine oocytes in in vitro maturation (IVM) and embryo production. In total, 1222 cumulus–oocyte complexes were cultured in TCM-199+ alone (control treatment) or supplemented with carvacrol at the concentrations of 3 µM (Carv-3), 12.5 µM (Carv-12.5), or 25 µM (Carv-25). After IVM, the oocytes were subjected to in vitro fertilization and embryo production, and the spent medium post-IVM was used for evaluating the levels of reactive oxygen species and the antioxidant capacity (2,2-diphenyl-1-picryl-hydrazyl-hydrate and 2,2′-azinobis-3-ethyl-benzothiozoline-6-sulphonic acid quantification). A greater (P < 0.05) antioxidant potential was observed in the spent medium of all carvacrol-treated groups compared with the control medium. Moreover, the addition of carvacrol to the maturation medium did not affect (P > 0.05) blastocyst production on days 7 and 10 of culture; however, the total number of cells per blastocyst was reduced (P < 0.05) in two carvacrol-treated groups (Carv-3 and Carv-25). In conclusion, carvacrol demonstrated a high antioxidant capacity in the spent medium after oocyte maturation; however, although embryo production was not affected, in general, carvacrol addition to IVM medium reduced the total number of cells per blastocyst. Therefore, due to the high antioxidant capacity of carvacrol, new experiments are warranted to investigate the beneficial effects of lower concentrations of carvacrol on embryo production in cattle and other species.