New methods for the recovery of oocytes from bovine ovarian tissue in relation to in vitro maturation and fertilization.

Bovine oocytes recovery from ovarian tissue after aspiration of visible fol-licular oocytes (3-5 mm in diameter) was performed using razor (s) or grater to obtain a large number of oocytes. The recovered oocytes were classified into 5 types based on their morphology in relation to the zona pellucida and surrounding cumulus cells. They were then cultured in vitro to investigate their ability to mature and become fertilized. The total number of follicular oocytes was 9.4 per ovary and the number of type A oocytes which showed complete layers of cumulus cells was 5.3 per ovary (56.4%). The total number of oocytes recovered from the ovarian tissue in each treatment ranged from 13.0-24.6 per ovary and the number of type A oocytes was 3.8-6.3 per ovary (13.4-38.3%). Using a grater with a small edge was found to be the most effective method for the recovery of type A oocytes inclinding several small intact follicles 0.45-1.35 mm in diameter. Type A oocytes recovered from ovarian tissue showed high ability to mature (81.1%) and become fertilized (63.3%) in vitro. The study indicated that it may be possible to recover more than 10 normal oocytes per ovary, which are able to mature and could be fertilized in vitro.