Development and viability of pig oocytes matured in a protein-free medium containing epidermal growth factor

This study examined the ability of epidermal growth factor (EGF) to improve the developmental competence of pig oocytes matured in a protein-free (PF) in vitro maturation (IVM) system. Oocyte maturation was done in one of thr ee media: 1. PF-TCM: tissue culture medium (TCM) 199 + 0.1% polyvinylalcoho l (PVA); 2. PF-TCM+EGF: PF-TCM + 10 ng/ml EGF; and 3. +ve CONT: North Carol ina State University (NCSU) 23 medium + 10% porcine follicular fluid. All m edia contained 0.57 mM cysteine. Hormonal supplements, 0.5 mug/mL LH and 0. 5 mug/mL FSH, were present only for the first half (20 to 22 h) of the cult ure period. After maturation, ocytes were co-incubated with frozen-thawed s permatozoa for 5 to 6 h and transferred to embryo culture medium,NCSU 23 co ntaining 0.4% BSA, for 144 h. In Experiment 1, differences in cumulus expan sion were observed for oocytes matured in +ve CONT (Category 4), PF-TCM (Ca tegory 2) and PF-TCM+EGF (Category 3). However, no significant differences in nuclear maturation to metaphase II stage were observed. In Experiment 2, no differences in fertilization parameters were observed. Significant (P < 0.01) differences in cleavage rates were observed among the three media fo r a proportion of the oocytes matured (52, 60 and 69% in PF-TCM, PF-TCM+EGF , and +ve CONT, respectively). Oocytes matured in PF-TCM showed the lowest (P < 0.01) blastocyst development (22%). However, the same rate of blastocy st development was obtained for +ve CONT (37%) and PF-TCM+EGF (37%). Blasto cyst cell numbers were significantly higher when oocytes were matured in th e presence of EGF (26 vs. 37 to 41). In Experiment 3, oocytes matured in PF -TCM+EGF had a significantly (P < 0.05) higher intracellular glutathione (G SH) concentration (5.9 vs. 11.4 pmol/oocyte) compared with PF-TCM. Twenty-t wo of 25 embryo transfer recipients became pregnant (Experiment 4). Four an imals returned to estrus in within 60 days. Six pregnant animals slaughtere d at 26 to 45 days had 43 fetuses (range: 4 to 12) and the remaining 12 ani mals farrowed 82 piglets (range: 3 to 12). These results indicate that EGF enhances the developmental competence of pig oocytes matured in a protein-f ree culture medium which is correlated with higher GSH level in oocytes. Bi rth of piglets indicate that embryos derived from oocytes matured in the pr esence of EGF are viable. (C) 2000 by Elsevier Science Inc.