Summary. Early bovine embryos (1- to 8-cell stages) were recovered from superovulated heifers at slaughter on Days 2 or 3. Embryos were cultured for 3–4 days in Medium B2 supplemented with 15% (v/v) fetal calf serum in the absence (B2SS, 106 embryos) or presence of trophoblastic vesicles (B2SS + TV, 190 embryos).
At the end of culture, there were more (P < 0·001) morulae (≥16 cells) in B2SS × TV (46%) than in B2SS alone (18%) irrespective of the initial cell stage. More 8-cell embryos reached the 16-cell stage than did embryos with <8 cells (30% vs 15% in B2SS, P > 0·05; 70% vs 41% in B2SS + TV, P < 0·005). After culture, 102 morulae were transferred non-surgically to temporary recipient heifers (84 embryos cultured in B2SS + TV and 18 in B2SS). After 2 or 3 days, 14 out of 58 embryos from the B2SS + TV group and 3 out of 10 embryos from the B2SS group were recovered as blastocysts. Most blastocysts were deep-frozen and stored for several weeks. After thawing, 10 apparently normal embryos from the B2SS + TV group were transferred non-surgically into 10 recipient heifers. Four pregnancies were induced, but only one embryo survived to term (birth of a normal male calf).
It is concluded that trophoblastic vesicles release one or several unknown compound(s) normally present in vivo, promoting the cleavage of early bovine embryos.