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, immature oocyte aspect under light microscopy has been paid little attention in the equine. The aim of the study is to give a general description and analyse 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 estral activity, follicle maturity, cumulus cells aspect, polarity and granulosity of ooplasm was observed. Thickness of zona pellucida differs between oocytes with polar or non polar ooplasm. No correlation was observed between follicle diameter and oocyte diameter and none of the other studied parameters showed an influence on oocyte diameter.
Results show that no character of oocytes observed under light microscopy can be related to follicular origin or to any other character. Further studies have to be done to compare these immature oocytes with mature oocytes and to find the ultra-structural origin of characters observed under light microscopy.