Influence of epidermal growth factor on in vitro maturation of equine oocytes

The effect of epidermal growth factor (EGF) on the in vitro maturation rate of equine oocytes was examined. Oocytes were collected from an abattoir (Expt 1) or using ultrasound-guided follicular puncture in vivo (Expt 2). All oocytes with a compact or expanded cumulus at recovery were cultured for 30 h in: medium 1 (TCM199 + fetal calf serum (FCS) + crude equine gonadotrophin (CEG) + oestradiol + antibiotics); medium 2 (TCM199 + EGF); medium 3 (medium 1 without FCS + EGF); or medium 4 (medium 1 without CEG + EGF). In Expt 1, 84% (37/44) and 87% (40/46) cumulus expansion (P > 0.05), and 39% (22/57) and 9% (5/57) (P < 0.01) nuclear maturation, were observed in medium 1 and 2, respectively. In Expt 2, cumulus expansion was observed after culture in medium 1, 3 and 4 (30/30, 31/31 and 29/29, respectively). The nuclear maturation rate was significantly lower in medium 3 (6%, 2/36) than in medium 1 (43%, 16/37) (P < 0.01) and was higher in medium 4 (64%, 25/39) than in medium 1, although the effect was not significant (P = 0.07). In conclusion, 50 ng EGF ml(-1) alone was an effective substitute for crude equine gonadotrophin and the presence of EGF improves the nuclear maturation rate of equine oocytes.