The influence of oxygen concentration on canine oocyte nuclear maturation in vitro.
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In this study the influence of oxygen concentration on the oocyte maturation in dogs was investigated. Ovaria were collected from 16 bitches undergoing elective ovariectomy and the cumulus oocyte complexes (COC) were collected. COC’s were matured in synthetic oviductal fluid (SOF) supplemented with luteinizing hormone (LH), follicle stimulating hormone (FSH) and progesterone (P4). 85 oocytes were cultured in group 1 in a humidified environment at 38.7°C, 5% CO2, 7% O2. 88 oocytes were cultured in group 2 in a humidified environment at 38.7°C, 5% CO2, 20% O2. After 72 hours of culture oocytes were stained with Hoechst 33342 and the nuclear maturation stage was determined. Oocytes were classified as germinal vesicle (GV), germinal vesicle breakdown (GVDB), metaphase I (MI), metaphase II (MII), degenerated (D) and not definable (ND). After 72h of culture, the percentages of oocytes still at the GV stage did not differ between both groups (7% O2, 20% GV vs 20% O2, 22% GV). However, the percentage of oocytes that had matured up to the MII stage was significantly (p<0.05) higher after culture in 7% O2 compared to culture 20% O2 (7.7% vs 0% respectively). It is concluded that maturation of canine oocytes in a low oxygen environment is beneficial for nuclear maturation.