In vitro embryo production in wood bison (Bison bison athabascae) using in vivo matured cumulus-oocyte complexes
Cervantes, M.P., Palomino, J.M., Anzar, M., Mapletoft, R.J., Mastromonaco, G.F., Adams, G.P. (2017). In vitro embryo production in wood bison (Bison bison athabascae) using in vivo matured cumulus-oocyte complexes. Theriogenology, [online] 89 122-130. http://dx.doi.org/10.1016/j.theriogenology.2016.10.017
Plain language summary
The population of wood bison in Canada is declining and under threat of extinction due to extensive hunting in the past and two endemic diseases, brucellosis and tuberculosis at present. The conservation of genetic diversity of wood bison is essential to repopulate these animals. The objective of this study was to produce wood bison embryos in lab. Two experiments were conducted in this study. The eggs (oocytes) were collected from bison cows after in vivo maturation for 30 hr or 34 hr. In both maturation groups, the embryo development rate was higher in 34 hr group than 30 hr (45% vs. 18%). In second experiment, the oocytes were matured in vivo for 30 hr or 34 hr. Eggs in 30 hr in cow maturation were further incubated for 4 hr in lab. Additional 4 hr incubation in lab improved the embryo development rates from 37% 54% in long incubation. Longer maturation in cows is beneficial for bison embryo production in lab.
Experiments were conducted in wood bison to determine the effect of additional maturation time on embryo development of in vivo matured oocytes. In experiment 1, cumulus-oocyte complexes (COC) were collected 30 hours after hCG treatment in superstimulated wood bison, and expanded COC were fertilized immediately or after 4 hours of additional in vitro maturation. Embryo development was assessed on Days 3, 7, and 8 (Day 0 = day of fertilization). No difference in cleavage rate was detected (55.3% vs. 60.5%, P = 0.82), but the Day 8 blastocyst rate was higher after an additional 4 hours of in vitro maturation time (44.7 vs. 18.4%, P = 0.03). In experiment 2, COC were collected at either 30 hours or 34 hours after hCG treatment. Expanded COC from the 30 hours group were fertilized after 4 hours of in vitro maturation, whereas those from the 34 hours group were fertilized immediately. A higher cleavage rate (74.3 vs. 57.0%) and blastocyst rate (54.1 vs. 37.2%) were found in the 34 hours group versus the 30 hours group (P < 0.05). In conclusion, an additional short period of in vitro maturation, or an extended period of in vivo maturation are beneficial for in vitro embryo production in wood bison.