Microscopic study of equine oocyte maturation within quaternary follicles

In various species a relationship between oocyte maturity and morphological characteristics of oocytes has been established. To our knowledge, little
attention has been paid to the immature oocyte aspect under light microscopy in the equine. The aim of the study is to give a general description and analysis
of the microscopic parameters of immature oocytes.
Follicles from abattoir ovaries are punctured after measurement of their diameter and their cumulus-oocyte complexes are recovered. Different characters
such as oocyte diameter, cumulus aspect, granulosity and polarity of ooplasm are observed under light microscopy.
No correlation between the estral activity, follicle maturity, cumulus cells aspect, polarity and granulosity of ooplasm was observed. The thickness of zona pellucida differs between oocytes with polar or nonpolar ooplasm. No correlation was observed between the follicle and oocyte diameter and none of the other studied parameters showed an influence on the oocyte diameter.
Results show that no character of the observed oocytes under light microscopy can be related to the follicular origin or to any other character. Further studies have to be done to compare these immature oocytes with mature ones and to find the ultrastructural origin of the characters observed under light microscopy.