Determination of optimal follicular size for obtaining the most quality oocytes for in vitro fertilization

Sa？etak The aim of this study was to determinate optimal follicular size for collection of high quality oocytes, and the subsequent capacity of the oocyte to mature and be fertilized and to develop in vitro. The ovaries of dairy cows were cut out immediately after slaughter and transported within one hour. The follicles were separated and divided into three groups according to diameter, i.e. small (3-5 mm), medium-size (6-9 mm), large (10-20 mm). Quality grading (A, B, C, D) of the oocytes was performed on the basis of cumulus cell development and homogeneity of cytoplasm. A total of 284 COCs were aspirated from 123 ovaries. Among 143 COCs, 236 were grades A and B and 48 were grades C and D. The maturation rate of the oocytes from medium size follicles A and B grade was 56.01% better than C and D grade. Only A and B graded oocytes were fertilized in vitro with 1×106 sperm/mL using Fert-TL, with 0.3% BSA, 22 μg/mL sodium pyruvate, 10 μg/mL heparin. The cleavage rate in the small follicle oocytes was significantly lower (35.89%) than in the medium-size follicle oocytes (56.41%), and a similar trend was observed in the morula development rates, independent of the oocyte grade. Good quality oocytes received from medium size follicles, and oocytes with more than three complete layers of cumulus cells (Grades A and B) have better competence for in vitro maturation and cleavage