32 Low oxygen tension during in vitro oocyte maturation and fertilisation improves cryotolerance of bovine blastocysts produced in vitro
F. Báez A , V. de Brun B , N. Rodríguez-Osorio C and C. Viñoles DA Instituto Superior de la Carne, Centro Universitario Regional Noreste, Universidad de la República, Tacuarembó, Uruguay
B Laboratorio de Endocrinología y Metabolismo Animal, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay
C Departamento de Ciencias Biológicas, Unidad de Genómica y Bioinformática, Centro Universitario Regional Litoral Norte, Universidad de la República, Salto, Uruguay
D Centro de Salud Reproductiva de Rumiantes en Sistemas Agroforestales, Centro Universitario Regional Noreste, Universidad de la República, Cerro Largo, Uruguay
Reproduction, Fertility and Development 34(2) 251-251 https://doi.org/10.1071/RDv34n2Ab32
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Mammalian embryonic development in vivo occurs in the female reproductive tract under low oxygen tension. Conducting all phases of in vitro embryo production under low oxygen tension could better simulate the maternal environment and improve embryo quality and cryotolerance. This study was conducted to evaluate the effect of physiological (5%) oxygen tension and the widely used atmospheric (20%) oxygen tension during IVM and IVF on the developmental competence of bovine oocytes and the quality and cryotolerance of the obtained embryos. Cumulus-oocytes complexes were matured and fertilised in 5% (IVM-IVF5) or 20% (IVM-IVF20) O2 tension. Presumptive zygotes from both groups (n = 311–354 per group) were cultured in vitro at 5% O2 and 5% CO2 for 8 days in synthetic oviducal fluid medium, supplemented with bovine serum albumin, in the absence of fetal calf serum. Expanded blastocysts of grade 1 and 2 (n = 36–54 per group) from both treatments were vitrified with ethylene glycol and dimethyl sulfoxide in Fibreplugs (CryoLogic) for at least 1 week in liquid nitrogen. After thawing, blastocysts went back to the same in vitro culture conditions for a further 24 h. Cleavage and blastocyst rates, cell count in fresh (n = 10–14 per group) or vitrified/warm (n = 10–12 per group) expanded blastocysts, and post-thawing re-expansion and hatching rates were compared using a one-way ANOVA with Tukey’s test. Low O2 tension during maturation and fertilisation significantly increased cleavage (89.26 ± 0.66% vs. 82.48 ± 2.35%; P = 0.016) and blastocyst (36.7 ± 1.76% vs. 29.16 ± 0.9%; P = 0.009) rates. Cell numbers were similar for blastocysts from IVM-IVF5 (146.21 ± 3.46) and IVM-IVF20 (134.66 ± 4.28; P = 0.069) groups. After vitrification and thawing, no differences were observed in re-expansion rates at 2 h (93.33 ± 3.33 vs. 96.66 ± 3.33; P = 0.89) and 24 h (94.44 ± 2.93 vs. 95 ± 5; P = 0.92) in the low and high oxygen groups, respectively. However, both hatching rate (41.66 ± 4.4 vs. 18.88 ± 1.1; P = 0.007) and cell number (108.2 ± 2.93 vs. 95.66 ± 2.96; P = 0.007) were higher in the IVM-IVF5 group. In conclusion, low O2 tension during IVM and IVF improves bovine oocyte competence, leading to better embryo development rates and improved cryotolerance.
