Equine compact cumulus oocytes for in vitro reproductive technologies : meiotic competence improvement and relationship with nutritional status and puberal development

The aim of this thesis was to investigate cellular processes critical to equine maturation, fertilization and embryo development in vitro. Equine compact cumulus oocytes (CCO) in vitro have low competence, so we evaluated the efficacy of a pre-maturation step in improving the coordination of cytoplasmic and nuclear maturation of CCO by the addition of Roscovitine and our results showed partial improving of the competence of these oocytes. Moreover, we carried out a study to examine the immunolocalization of leptin (Ob) and leptin receptor (Ob-R) in CCO recovered from fillies and from mares of light vs heavy body weight breeds after slaughtering and to further improve the maturation rate of CCO we supplemented the maturation medium with leptin and investigated its effect in expanded and compact cumulus oocytes on maturation, fertilization and embryo cleavage rates after intra cytoplasmic sperm injection (ICSI). The results supported the hypothesis that, in the horse, leptin is differently localized during oocyte IVM showing different immunoreaction intensity related either to the horse breed or to the reproductive puberal development. In vitro, the presence of leptin during oocyte maturation improves the progression of meiosis and the rate of fertilization after ICSI but, by contrast to other species, in our horse model no differences were detected in the subsequent development rates of embryos: probably species-differences exist in embryos with regard to sensitivity to leptin.