68 Developmental competency of bovine embryos derived from oocytes with granulated ooplasm after in vitro culture

Although it has been well accepted that oocytes with homogeneous ooplasm are suitable for IVM, a lot of bovine oocytes collected by transvaginal follicular aspiration have dark granules in the ooplasm and their developmental competency is not clear. The aim of this study was to determine the preimplantation competency of bovine embryos derived from oocytes with granulated ooplasm after IVF and culture. Slaughterhouse-derived cumulus-oocyte complexes (COCs) surrounded by compact cumulus cell layers were selected and grouped as follows: (1) oocytes with homogeneous ooplasm (H group), and (2) oocytes with dark granulated ooplasm (Gr group). All COCs were matured for 22 h in TCM199 (supplemented with 0.125% bovine serum albumin, FSH, LH, and epidermal growth factor), subsequently fertilised (20 h), and cultured until Day 8 post-IVF. The cleavage rate (24 h and 48 h post-IVF), blastocyst formation (Day 7 post-IVF), cell number of blastocyst (Day 7 post-IVF) and mRNA expression of interferon-tau (IFN-t) (Day 8 post-IVF) were analysed by t-test (GraphPad Prism 8; GraphPad Inc.). The cleavage rate at 48 h post-IVF was not different between groups (92.5% and 94.9%, respectively, P = 0.2156), but the ratio of embryos cleaved early before 24 h was higher in the Gr group (187/331 = 56.9%) than in the H group (171/404 = 42.0%; P < 0.05) and fewer embryos cleaved after 27 h in the Gr group (42/331 = 12.6%) than in the H group (77/404 = 19.2%; P < 0.05). The total blastocyst rate of Gr group embryos (205/348 = 59.5%) was significantly higher than that of H group embryos (206/436 = 46.8%; P < 0.05), but the total cell number of blastocysts in the Gr group was not different from that of embryos in the H group (124.5 and 105.2, respectively; P = 0.083). The ratio of blastocysts derived from early cleaved embryos to total blastocysts was higher in Gr (143/205 = 67.4%) than in H (100/206 = 48.6%; P < 0.05). The blastocyst rate of early cleaved embryos in Gr (74.8%) was higher than that of H (57.6%; P < 0.0005). In quantitative PCR analysis of Day 8 blastocysts, relative mRNA expression of INF-t was not different between Gr group embryos and H group embryos (P = 0.3256). In conclusion, oocytes with granulated ooplasm cleaved faster than those with homogenous ooplasm after IVF and had sufficient developmental competency to preimplantation stage blastocysts. Although the expression level of IFN-t in embryos derived from granulated oocytes was not different from that derived from homogenous oocytes, further studies for evaluation of embryo quality are necessary to fully understand the pre- and postimplantation competency of oocytes with granulated ooplasm.

This research was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (IPET) through the Agriculture, Food and Rural Affairs Convergence Technologies Program for Educating Creative Global Leader Program funded by the Ministry of Agriculture, Food, and Rural Affairs (MAFRA; 120011-02-2-CG000).