In vitro-production of embryos using immature oocytes collected transvaginally from superstimulated wood bison (Bison bison athabascae)
Cervantes, M.P., Palomino, J.M., Anzar, M., Mapletoft, R.J., Mastromonaco, G.F., Adams, G.P. (2017). In vitro-production of embryos using immature oocytes collected transvaginally from superstimulated wood bison (Bison bison athabascae). Theriogenology, [online] 92 103-110. http://dx.doi.org/10.1016/j.theriogenology.2017.01.017
Plain language summary
Canadian wood bison has threat of extinction. In the past, they underwent extensive hunting and now they are facing to endemic diseases (tuberculosis and brucellosis). Therefore, the strenuous efforts are required to save this Canadian species. The objectives of this study were to assess if the appearance of wood bison egg under microscope can predict their subsequent embryo development and if wood bison eggs can be harvested and matured during non-breeding season. In this study, eggs were harvested from superstimulated bison cows during non-breeding season and were graded as compact, expanded and denuded. Eggs were matured in vitro 24 h. The blastocyst rate was 7/34, 2/10 and 0/3 in compact, expanded and denuded eggs. This study indicated that morphology of eggs can reflect the subsequent embryo development and embryos can be produced from bison cows during non-breeding season.
Two experiments were done to test the hypothesis that morphologic characteristics of wood bison cumulus-oocyte complexes (COC) are reflective of the ability of the oocyte to develop to an advanced embryonic stage after in vitro maturation, fertilization and culture, and to determine the effect of prolonging the interval from the end of superstimulation treatment to oocyte collection (FSH starvation period). Experiments were done during the anovulatory season. In Experiment 1, ovarian superstimulation was induced in 10 bison with two doses of FSH given at 48 h intervals beginning at the time of follicular wave emergence. COC were collected 3 days (72 h) after the last dose of FSH by follicular aspiration and classified as compact, expanded or denuded. The COC were matured in vitro for 24 h before fertilization in vitro (Day 0). Embryo development was assessed on Days 3, 7 and 8. The blastocyst rate was 7/34, 2/10 and 0/3 in COC classified as compact, expanded and denuded, respectively; however, only compact COC resulted in embryos that reached the expanded blastocyst stage. In Experiment 2, COC were collected at either 3 or 4 days (72 or 96 h) after the last dose of FSH (n = 16 bison/group) to determine the effect of the duration of FSH starvation on oocyte competence. The COC were classified as compact good (>3 layers of cumulus cells), compact regular (1–3 layers of cumulus cells), expanded or denuded, and then matured, fertilized and cultured in vitro. Although follicles were larger (P < 0.05) in the 4-day FSH starvation group, there was no effect of starvation period on the distribution of COC morphology; overall, 112/194 (57.7%) were compact, 29/194 (26.3%) were expanded, 39/194 (20.1%) were denuded, and 14/194 (7.2%) were degenerated (P < 0.05). Similarly, there was no effect of starvation period on embryo development. Compact good COC had the highest cleavage (88%) and blastocyst rates (54%; P < 0.05), followed by compact regular COC at 73% and 25%, respectively. Expanded and denuded COC had low cleavage (40% vs. 59%, respectively) and blastocyst rates (5% vs. 8%, respectively). We conclude that morphologic characteristics of wood bison COC are reflective of the ability of the oocyte to develop into an embryo in vitro. Importantly, oocytes collected from superstimulated bison during the anovulatory season were competent to develop to the blastocyst stage following in vitro maturation, fertilization and culture.