Development of bovine embryos produced in vitro from the one-cell to the blastocyst stage in serum-free oviduct-conditioned medium was five\p=n-\eight-cell), the higher the probability that they developed into morula\p=n-\blastocyst: 70% of the embryos reaching the two-cell stage before 30\p=n-\31h after insemination developed into morula\p=n-\blastocyst. We suggest that the lag-phase as well as the link between early cleavage kinetics and further development could be related to the transcriptional activity of the embryo at about the 5\p=n-\8-cell stage.

The effects of fetal calf serum (FCS)

Bovine zygotes, obtained after in vitro maturation and fertilization of oocytes from slaughtered cow ovaries, were cultured in droplets of nonconditioned or conditioned medium on bovine oviduct cell monolayers. The media tested were Medium 199 alone and Medium 199 supplemented with 10% fetal calf serum (FCS). Oviduct conditioning increased both early cleavage and development to blastocysts. Only the effect on early cleavage was mimicked by FCS. The blastocysts obtained in serum-free conditioned medium (SFCM) appeared morphologically normal and had the same cell number as those produced in conditioned medium containing serum. Their hatching rates did not differ. Transfer of 16 blastocysts developed in SFCM to 16 synchronized recipients resulted in five pregnancies (31%), indicating good embryonal viability. Boiling of SFCM resulted in a total loss of activity, while heating at 56 degrees C for 30 min had no deleterious effect. A 10-kDa ultrafiltration of SFCM removed the blastocyst development-supporting activity from the filtrate but not the early cleavage-favoring activity. This allows us to conclude that at least two different factors are present in SFCM: one of low molecular mass (< approximately 10 kDa), needed to obtain the 5-8 cell stage and mimicked by FCS, and another of higher molecular mass allowing embryos to develop from the 8-cell to blastocyst stage.

No abstract

No abstract