In vitro maturation and degeneration of domestic cat oocytes collected from ovaries stored at various temperatures

Cat oocytes have the unique ability to mature in vitro after temporary storage at 4°C which can provide opportunities to rescue oocytes from the ovaries of endangered felids after sudden death or medical ovariohysterectomy. It has been demonstrated that factors such as season, culture conditions and morphological quality of oocytes influence the meiotic competence of domestic cat oocytes. In the present study we determined the meiotic maturation rate and incidence of apoptosis or necrosis in domestic cat oocytes collected from ovaries stored at different temperatures. Nuclear status and the presence of the first polar body were evaluated by fluorescence DAPI staining. Cell death was detected using Annexin-V, a phospholipid-binding protein that detects translocation of phosphatidyl-serine to the outer cytoplasmic membrane. Most oocytes (77.5%) collected from ovaries immediately after ovariohysterectomy (control group) resumed meiosis and reached metaphase II. A similarly high percentage of oocytes underwent nuclear maturation after recovery from ovaries stored for 6 h at 4°C (68.6%) or at room temperature (55.5%), but the rate of maturation after recovery from ovaries stored for 24 h at 4°C was greatly reduced (15.3%) Not surprisingly, the highest percentage of apoptotic oocytes were seen in Group 3, and the lowest frequency of apoptotic oocytes were observed in Group 1. Correspondingly, Group 1 had the highest percentage of necrotic oocytes. Thus, our results indicate that storage of domestic cat ovaries at room temperature, even for a short time, can negatively influence the competence of oocytes to undergo nuclear maturation in vitro.