PREINCUBATION OF CUMULUS-OOCYTE COMPLEXES BEFORE EXPOSURE TO GONADOTROPINS IMPROVES THE DEVELOPMENTAL COMPETENCE OF PORCINE EMBRYOS MATUREDAND FERTILIZED IN-VITRO

The objectives of the present study were to examine whether delayed ex posure of porcine cumulus-oocyte complexes (COCs) to gonadotropins aff ects the diameter of oocytes, the nuclear morphology of the germinal v esicle, the rate of germinal vesicle breakdown (GVBD), and the embryon ic developmental rate of inseminated oocytes following maturation and fertilization in vitro (IVM/IVF). After preincubation (experimental) o r no preincubation (control) in BSA-free NCSU23 medium containing 10% porcine follicular fluid for 12 h, COCs were cultured for maturation i n the same medium supplemented with gonadotropins for 20 h and then wi thout those gonadotropins for 20 h. During the preincubation period, t he nuclear morphology of the germinal vesicles became more homogeneous . Incidence of GVBD after 20 h of maturation culture was not different between the control and experimental group. When cultured in NCSU23 m edium for 7 d following IVF, the incidence of embryos that developed t o the blastocyst stage (23.1 +/- 3.1%) was higher in the experimental group than in the control group (8.7 +/- 1.2%). Blastocysts in the exp erimental group had a larger number of cells than control blastocysts. Following embryo transfer into the oviduct of recipient gilts, IVM/IV F embryos had elongated by Day 12 of gestation. These results indicate that preincubation of porcine COCs, before exposure to gonadotropins to induce the resumption of meiosis, increases the rate of development of IVM/IVF embryos to the blastocyst stage. (C) 1997 by Elsevier Scie nce Inc.