Equine oocyte vitrification before in vitro maturation

Oocyte cryopreservation is the option of choice for genetic preservation of female mammals. In particular, the equine oocyte is very susceptible to classic freezing technique, so different vitrification protocols have to be developed. The purpose of this study is to vitrify immature oocytes, from slaughtered mares ovaries, then to allow them to mature and to activate in vitro. In this way the meiotic competence will be tested. 111 cumulus-oocyte complexes (COCs) were vitrified in Open Pulled Straw (OPS), then the 97 COCs considered suitable after thawing were subjected to In Vitro Maturation (IVM), as previously described by the Authors(9,10). In total, the 30.93% of cases were considered mature. 118 fresh COCs were the control samples and they have provided the 57.63% of maturity. The mature oocytes of both groups were subjected to parthenogenetic activation using ionomycin and 6-dimethylaminopurine. They were cultivated in Synthetic Oviductal Fluid (SOF) for a few days at 38.5 degrees C, 5% O-2 and 5% CO2. 72h after activation, the 24.14% of the oocytes were vitrified and 80.00% of the control samples showed signs of segmentation. The Fisher Exact Test was applied to both groups of in vitro maturated and activated samples and they showed a highly significant degree of association (p < 0.0001). Our results about IVM do not differ from those described by bibliography(5,15). The activation also showed further loss of meiotic competence of vitrified COCs. Having achieved good results in fresh IVM, our next step will be the vitrification of mature gametes, assuming that they maintain higher meiotic competence after thawing.