Abstract:

The aim was to explore the efficience of in vitro fertilization and embryo development of the cattle-yak. The experiment was conducted to investigate the effects of in vitro maturation time, oocyte grades, different treatment methods of the semen, in vitro culture system and embryonic vitality and development after freezing and thawing on in vitro fertilization cattle×yak. The results showed that following the prolonging of in vitro maturation time, the extruding of the first polar body(Pb1) increased. And the Pb1 of grade A oocytes cultured in 24 h was significantly higher than that of B and C grade oocytes. But there was no significant difference between cattle oocytes and yak oocytes in same culture time and grade. Cleavage rate with BO fluid washing centrifugal process group is significantly higher than that of the Percoll group, but no significant differences on the blastocyst rate. Two kings of IVF cattle-yak embryos(cattle♀×yak♂vs. yak♀×cattle♂) co-culture with oviductal epithelial cells, cumulus cells and SOF medium and there was no significant difference in cleavage rate, but blastocyst rate and hatched blastocyst rate of co-cultured group were significantly higher than that of SOF medium group. The rate of normal morphology embryo (90.52%±5.94% vs. 91.53%±7.34%), survival rate within 24 h (61.45%±8.44% vs.64.72%±11.82%) or 48 h(44.81%±6.21% vs. 48.47%±10.04%) of the embryos after thawing were no significant difference. Taking 7 bovines including 4 yellow cattle and 3 cattle×yak as recipients, which were transplanted after natural estrus .The pregnancy rate was 57.14% and the length of average pregnancy was 258 days.