Relationship of morphology and follicular fluid environment of bovine oocytes to their developmental potential in vitro

Abstract

Morphology of bovine cumulus oocyte complexes (BCOC) and follicular fluid parameters were examined as potential criteria for selecting in vitro developmentally competent oocytes. Immature BCOC, from antral follicles, exhibiting similar morphological characteristics were grouped and the blastocyst development for oocytes in each group was examined. In a second experiment, follicles were individually aspirated to recover BCOC with their associated follicular fluid. Each oocyte was categorized and individually matured, fertilized and cultured. Radioimmunoassays for follicular progesterone, estradiol-17β and insulin-like growth factor-I (IGF-1) concentrations were performed. The BCOC were categorized into 9 groups based on the homogeneity of the ooplasm, compactness of the cumulus investment, color and size. Oocytes classified into Groups 1, 2 and 3 demonstrated the highest rates of development to the blastocyst stage at 13, 16 and 20%, respectively. Therefore, Groups 1, 2 and 3 were pooled and designated as the enhanced developmental potential (EDP) group, and the remaining groups were designated as the reduced developmental potential (RDP) group. The progesterone concentration (± SEM) in follicles containing EDP oocytes (27.54 ± 5.08 ng/ml) was significantly lower than the RDP group (72.72 ± ng/ml; P < 0.001). Follicles containing oocytes that developed to the blastocyst stage (28.65 ± 7.18 ng/ml) possessed significantly lower progesterone levels than all remaining follicles (52.9 ± 7.51 ng/ml; P < 0.05). No significant differences were found for estradiol-17β or IGF-I concentrations between the EDP and RDP groups or developmental stages. These results indicate that morphological criteria and follicular fluid progesterone concentration may be used to select BCOC for high potential of blastocyst development.