Jacqueline Bézard

Comparative Evaluation of Nuclear Morphology of Equine Oocytes Aspirated in vivo and Stained with Hoechst and Orcein

Nuclear maturation of equine oocytes was assessed immediately after in vivo collection. A double-staining technique (Hoechst and orcein) was used on the same oocytes to visualize nuclear morphology, i.e. to evaluate the chromatin configurations of each oocyte after Hoechst in relation to the nuclear morphology after orcein staining. The proportion of oocytes evaluated as germinal vesicle stages was significantly (p < 0.02) lower after Hoechst (14.5%) than after orcein staining (29.0%), while the incidence of the so-called dense chromatin stage was assessed to be higher (p < 0.05) after Hoechst than after orcein staining (14.5 vs. 6.5%). There was no difference between Hoechst and orcein staining in the incidence of diakinesis and germinal vesicle breakdown stages, respectively (44.9 vs. 42.0%), and the same applied for metaphase I (11.6 vs. 8.0%), metaphase II (7.2 vs. 8.0%) and degenerated stages (7.2 vs. 6.5%). It was concluded that the interpretation of the meiotic stages may differ between Hoechst and orcein staining and in a large proportion of equine oocytes the nuclear border may not be visualized on orcein staining.