The effects of an estrus-associated oviductal glycoprotein on the in vitro fertilization and development of ovine oocytes matured in vitro

An estrus-associated glycoprotein (oEGP) secreted by the ampulla of the ovine oviduct for 3 to 6 d around the time of estrus is known to bind to the zona pellucida of newly ovulated oocytes, as well as embryos but does not appear to bind to spermatozoa. The objective of this paper was to establish whether or not the association of oEGP with the zona pellucida influences fertilization and subsequent embryo development. Four separate experiments were carried out to examine the specific effects of different concentrations (0, 2.5, 5.0, 10.0, 20.0% v/v) of an oEGP-enriched fraction of oviductal fluid (F1) in in vitro fertilization(IVF) medium. This medium was synthetic oviduct fluid (SOF) containing either no serum or supplemented with human serum (HS) or sheep serum. Fertilization did not occur in the absence of serum, while both cleavage rate and the developmental competence of embryos were significantly greater in SOF + sheep serum than in SOF + HS. The presence of F1 in the HS-containing medium significantly improved cleavage rates. The specificity of this effect was confirmed in a study which substituted F1 with a comparable concentration of BSA. In the IVF medium (SOF + sheep serum), the addition of F1 at a concentration of 10% significantly (P<0.05) increased cleavage rates compared with the control treatment. Culture of embryos with 2.5% F1 significantly decreased the proportions of blastocysts forming from cleaved embryos. Overall, the use of F1 in fertilization medium significantly increased the time taken for blastocyst formation.