Characterization of immature sheep oocytes and zona pellucida morphology using scanning electron microscope (SEM)

The aim of the present work was to study the differences among different categories of immature sheep oocytes. Oocytes were divided into three categories: excellent, good and fair oocytes. Results showed that cumulus cells were close to each other and zona pellucida in all the three oocytes categories. All oocytes categories with cumulus cells exhibited an irregular shape, mucous material inter-granular cells, low number of small droplets and minutes tapes on the cell surface. Good oocytes category was characterized by the presence of a belt surrounding the oocytes. Moreover, there are large numbers of small holes on the ZP surface in all categories. The good oocytes also contained a large number of big holes. In contrast, fair and excellent oocytes have low number of large holes in the ZP surface. In conclusion, there are several differences between oocytes categories in the morphology of oocytes and ZP characteristics. This study recommends using excellent and good oocytes in the in vitro embryo production for quality of the outer surface and integrity of zona pellucida than fair oocytes.