THE EFFECTS OF AN OVINE OVIDUCTAL ESTRUS-ASSOCIATED GLYCOPROTEIN ON EARLY EMBRYO DEVELOPMENT

Oviduct specific estrus-associated glycoproteins (EGP) secreted around the time of estrus are known to be present in several species. Many o f these glycoproteins, including that of the sheep (oEGP), have been s hown to bind to the zona pellucida and to become associated with indiv idual blastomere membranes, indicating a role for these proteins in ea rly embryo development. Given that the culture of ovine embryos can re sult in a number of developmental abnormalities as well as a reduction in viability, the present study examined the effects of oviducal flui d and gel filtration fractions of oviducal fluid on the in vitro devel opment of ovine embryos. The first fraction of oviducal fluid (F1) con tained predominantly oEGP, while the second (F2) contained albumin and was included in the study as a control. The culture medium was synthe tic oviduct fluid (SOF) supplemented with 20% human serum (HS). The st udy consisted of 2 experiments; the first examined the effects of ovid ucal 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 7 2 h of culture, examined the influence of oviducal fluid and the fract ions in the presence of either a low concentration of serum or no seru m for the first 72 h. The presence of F1 significantly decreased the p roportion of zygotes undergoing first cleavage, increased the mean num ber of nuclei per blastocyst and increased the mean time taken for bla stocyst formation. Unfractionated oviducal fluid appeared to be detrim ental to embryo development while F2 had no influence. The use of a lo w concentration of serum during the first 72 h of culture was not bene ficial to development. Removing F1 from the culture medium after the i nitial 72 h of culture did not reverse the effects of this protein, im plying that it is required only during the first 2 to 3 d of developme nt. It is postulated that oEGP is involved in a selection mechanism at the zygote stage and may improve the viability of in vitro cultured e mbryos.