Stereomicroscopic and histological examination of bovine embryos following extended in vitro culture.

Attempts to support survival of mammalian embryos after hatching have met with limited success, although some mouse studies have reported growth at the post-implantation stage. The aim of the present research was to establish and characterise an in vitro culture system that could support extended growth and differentiation of bovine embryos. Abattoir-derived oocytes were matured and fertilised in vitro. Presumptive zygotes were cultured in modified synthetic oviduct fluid (SOFaaci) medium supplemented with 5% cow serum (CS). On Day 9, single hatched blastocysts (n = 160) were randomly allocated to SOFaaci supplemented with either 5% bovine serum albumin, 5% CS, 5% fetal calf serum (FCS) or SOF only and cultured on a collagen gel substrate for up to 45 days. Embryos were evaluated at various time-points until complete disaggregation or the total disappearance of embryonic cells. Blastocyst viability post hatching was severely compromised in protein-free SOFaaci medium. Addition of FCS generated increased embryonic growth for the longest time period (Day 45) when compared to the other groups. Long-term survival of embryonic cells was observed stereomicroscopically by the proliferation and development of three-dimensional tubular structures to 85% confluence in culture. Haematoxylin and eosin staining of morphological structures obtained from all treatment groups revealed embryos displaying trophoblast, inner cell mass and hypoblast development to varying degrees. Regardless of treatment, extended in vitro culture did not result in development comparable with that described for in vivo embryos. In the present work, however, there was evidence of extended culture of bovine embryos beyond that achieved previously. However, further research is required to identify the exact requirements for extended in vitro culture for bovine embryos.