Increasing carbon dioxide from five percent to ten percent improves rabbit blastocyst development from cultured zygotes

One‐cell rabbit zygotes were cultured at 39°C in basal synthetic medium II (BSM‐II) with 5%, 10%, or 15% CO₂ and humidified air to determine the effect of CO₂ concentration on development in vitro. After 4 days in culture, 37% of the embryos grown in 10% or 15% CO₂ had reached the hatching blastocyst stage, but only 10% of the embryos were hatching when cultured under 5% CO₂ (P = 0.01). Over all blastocysts, cell numbers were 207, 246, and 205 for the 5%, 10%, and 15% CO₂ treatments, respectiveiy. In a second experiment to determine if there was a beneficial effect, particularly at the blastocyst stage, of a higher concentration of CO₂, embryos were cultured 4 days in either 5% or 10% CO₂ or for 2 days in 5% CO₂ followed by 2 days in 10% CO₂. The numbers of blastomeres per embryo and embryo diameter were greater (P > 0.05) in embryos cultured continuously in 10% CO₂ or in 10% CO₂ only during days 3 and 4 of culture than in embryos cultured continuously in 5% CO₂. In a third experiment, one‐cell rabbit zygotes were cultured with 5% or 10% CO₂ in a defined, protein‐free medium consisting of 1:1 RPMI 1640 and Dulbecco's modified Eagle's medium. The proportion of embryos hatching and cell counts were significantly greater (P > 0.01) when cultured in the presence of 10% CO₂. These data indicate that a 10% CO₂ atmosphere exerts a beneficial effect on the development of zygotes into expanding and hatching rabbit blastocysts in vitro. © 1992 Wiley‐Liss, Inc.