Evaluation of different culture systems with low oxygen tension on the development, quality and oxidative stress-related genes of bovine embryos produced in vitro.

The present study was conducted to assess the development, quality and gene expression profile of oxidative stress-related genes of bovine embryos cultured in different culture systems with low oxygen tension (5% CO2, 5% O2 and 90% N2). The systems assessed included: (1) an incubator chamber; (2) a plastic bag; and (3) a foil bag. The choice of culture system had no effect on cleavage rate at 72 h. However, significant differences (P < 0.01) were observed in the rate of blastocysts registered at day 7 (29.8, 20.2 and 12.7% for incubator chamber, plastic bag and foil bag, respectively). Total number of cells did not differ between systems, although the proportion of ICM:total cells was affected particularly in the plastic bag (19.5%), compared with the incubator chamber (31.4%). In addition, significant differences were found in the apoptotic:total cell ratio (3.3, 6.5 and 8.8% for the incubator chamber, plastic bag and foil bag, respectively), with apoptotic nuclei localised mainly in the ICM compartment of the embryo. The amount of reactive oxygen species was also different between culture systems and this effect was correlated with a higher expression of SOD2, GSS and GPX1 genes in embryos cultured in the gassed bags as compared with embryos cultured in the incubator chamber. In conclusion, these results give evidence that, under low oxygen tension, the incubator chamber is more efficient and generates higher number of, and better quality, embryos than gassed bag systems evaluated here and this effect was probably due to an increased level of reactive oxygen species in the gassed bags, which upregulates the expression of some antioxidant enzymes to compensate for hyperoxia conditions.