SELECTION OF IMMATURE BOVINE OOCYTES FOR DEVELOPMENTAL POTENTIAL INVITRO

These experiments were conducted to determine whether the compactness and quantity of follicle cells (corona radiata and cumulus cells) could be used as criteria for the selection of immature bovine oocytes for their developmental potential in vitro. Oocytes were divided into three categories: (1) oocytes surrounded by compact, multi-layers of follicle cells; (2 ) oocytes with compact layers of corona radiata cells only; (3) oocytes with less compact and fewer layers of follicle cells. The frequencies of normal penetration. cleavage to the 6-16-cell stage on Day 3 post-insemination and blastocyst formation by Day 8-10 were the endpoints for evaluation. Oocytes of each category underwent normal penetration at a similar frequency. Greater proportions of oocytes in Categories 1 and 2 cleaved (38.1% and 36.9%. respectively) compared to those in Category 3 (27.0%) (P = 0.014 and P = 0.010, respectively). Oocytes of Category 1 developed to the blastocyst stage at a significantly greater frequency than oocytes of Category 3 (24.5% and 14.9%, respectively, P = 0.010). The rate of blastocyst development for Category 2 was similar to that of Categories 1 and 3. The results presented indicate that visual assessment of the follicle cell investment surrounding immature bovine oocytes can be used to select oocytes most capable of embryonic development in vitro following maturation and fertilization in vitro.