Each month we will give a tip on how to improve your results, sourced either from the literature or our own research.
5% O2 Vs 7% O2 for Culture
Why do we recommend in our protocol culturing putative zygotes to the blastocyst stage in 7% O2, rather than 5% O2? Historically, 5% O2 was found to be optimum for mouse embryo culture. Then H. Robin Tervit, whilst studying for his PhD at Babraham, Cambridge, UK, in 1972, demonstrated for sheep and cattle embryo development in vitro, 5% was beneficial over 20% (air). But there were no studies examining a range of O2 levels, until Jeremy Thompson and Robin Tervit published in 1990 the most comprehensive study of O2 levels and embryo development in sheep and cattle, indeed in any species, which remains so to this day. Their results suggested the theoretical optimal O2 level is 7% for embryo culture. This makes physiological sense, as the ruminant embryo is 30% larger in diameter compared to the mouse and more metabolically active, so a slightly higher level is likely to assist O2 diffusion.
But is 5% less effective than 7%? There is no evidence (and proving so would be of limited interest) to claim 5% is any better or worse than 7%. What is critical is that, for embryo culture in sheep, cattle and most other mammalian species, a low O2 environment, around 5 – 7%, is provided.
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