Low oxygen tension during in vitro embryo production improves the yield, quality, and cryotolerance of bovine blastocysts

Abstract

Mammalian oocytes undergo maturation and fertilization in the low-oxygen (O₂) environment of the oviduct. To evaluate the effect of O₂ tension during in vitro maturation and fertilization on embryo yield, quality, cryotolerance, and gene expression, we matured and fertilized bovine cumulus-oocyte complexes under low (5%) or high (20%) O₂ tension. Presumptive zygotes from both groups were cultured at 5% O₂ for 8 days. Blastocysts were vitrified, and then warmed, and cultured for further 24 h to assess their cryotolerance. Our findings indicate that low O₂ during maturation and fertilization enhances embryo development and cell count in both fresh and vitrified/warmed blastocysts. In this study, the interaction of O₂ tension and status (fresh or vitrified/warmed) affected the transcript abundance of SOD2, AQP3, and BAX in blastocysts. These results highlight the role of low O₂ tension during bovine maturation and fertilization and provide support to using 5% O₂ throughout all stages of bovine in vitro embryo production.