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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 oviducial 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

Oviduct specific estrus-associated glycoproteins (EGP) secreted around the time of estrus are known to be present in several species. Many of these glycoproteins, including that of the sheep (oEGP), have been shown to bind to the zona pellucida and to become associated with individual blastomere membranes, indicating a role for these proteins in early embryo development. Given that the culture of ovine embryos can result in a number of developmental abnormalities as well as a reduction in viability, the present study examined the effects of oviducal fluid and gel filtration fractions of oviducal fluid on the in vitro development of ovine embryos. The first fraction of oviducal fluid (F1) contained predominantly oEGP, while the second (F2) contained albumin and was included in the study as a control. The culture medium was synthetic oviduct fluid (SOF) supplemented with 20% human serum (HS). The study consisted of 2 experiments; the first examined the effects of oviducal fluid, F1 and F2 in combination with 0, 10 and 20% HS; while the second, which aimed to investigate the effect of F1 during the first 72 h of culture, examined the influence of oviducal fluid and the fractions in the presence of either a low concentration of serum or no serum for the first 72 h. The presence of Fl significantly decreased the proportion of zygotes undergoing first cleavage, increased the mean number of nuclei per blastocyst and increased the mean time taken for blastocyst formation. Unfractionated oviducal fluid appeared to be detrimental to embryo development while F2 had no influence. The use of a low concentration of serum during the first 72 h of culturewas not beneficial to development. Removing F1 from the culture medium after the initial 72 h of culture did not reverse the effects of this protein, implying that it is required only during the first 2 to 3 d of development. It is postulated that oEGP is involved in a selection mechanism at the zygote stage and may improve the viability of in vitro cultured embryos.