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 of these glycoproteins, including that of the sheep (oEGP), have been shown to bind to the zone 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 F1 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 culture was 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.