A number of investigators (Fridhandler, 1961; Fridhandler, Hafez & Pincus, 1957; Pincus, 1941; Smith & Kleiber, 1950) have shown that rabbit ova require oxygen in cleavage stages but that the rate of consumption increases markedly at the blastocyst stage (Fridhandler, 1961). Mills & Brinster (1967) show a similar increase beginning at the 8-cell stage of the mouse. Presumably these observations are related to changes being made in respiratory pathways at this time and reflect increasing metabolic activity.
Embryo culturists typically use high concentrations of oxygen: New & Stein (1963) reported improved results when mouse embryos were grown in 60% oxygen, Pavlok (1967) used 95% for mouse ova growing in explanted oviducts and Huff & Eik-Nes (1966) used 95% oxygen to grow 6-day rabbit blastocysts. Conversely, Glenister (1967) feels that high concentrations of oxygen are detrimental to embryonic