Toronto, Canada (August 3, 2022) – If you have visited Toronto Zoo’s Canadian Domain recently, you’ve probably noticed some very special additions – three wood bison calves! Born the week of June 20th, there are two females and one male. These three little calves are quickly becoming a visitor favourite as they follow the much larger adult females around the paddock, peeking out behind their mothers’ legs.
What makes these little ones extra special is the innovative reproductive techniques that enabled Toronto Zoo to deliberately produce females!
How can Toronto Zoo choose whether to have females or males?
The amazing Toronto Zoo Reproductive Sciences team worked with researchers from the University of Saskatchewan for 13 years to advance assisted reproductive technologies for wood bison. Last year for the first time, the team partnered with Sexing Technologies to use highly sensitive equipment capable of sorting x- from y-bearing sperm in hopes of producing predominantly female calves this spring, an important step forward for the long-term sustainability of bison conservation herds.
Why is this important?
Although wood bison have been down listed from "endangered" to "threatened" since 1988, on-going diseases, such as tuberculosis and brucellosis, in wild wood bison populations continue to threaten this species. Reproductive technologies, such as artificial insemination and in vitro fertilization, are important tools for improving the genetic management and connectivity of small populations. These techniques will help Toronto Zoo overcome the challenges of managing the endemic disease threatening free-ranging wood bison herds, and ultimately allow us to restore genetically diverse disease-free herds in the wild.
“It’s wonderful to be able to contribute to a better future for wood bison through this critical research” says Gabriela Mastromonaco, Senior Director of Wildlife Science, Toronto Zoo. “Your Toronto Zoo houses one of a few reproductive physiology labs in North America that participate in biobanking wildlife species, freezing living cells such as sperm and embryos for the purpose of preserving genetic diversity for the future. Without wood bison, their landscape would be seriously altered and would ultimately threaten the community of species that co-exist with them”.
How does it work?
Your Toronto Zoo currently cares for a herd of 5 male and 18 female wood bison. From mid-September into December, the Zoo’s Reproductive Sciences team spent long days with the Wildlife Care team moving bison through our handling system to undergo artificial inseminations (AI) or embryo transfers (ET). Both AI and ET are extremely intricate processes. The survival of the previously frozen sperm and embryos are sensitive to the slightest changes in their environment, therefore, keeping them at the proper temperature is crucial.
The timing of each procedure was dependent on the bison’s ovulation cycles which were synchronized using hormone injections. This ensured the AI and ET of all females could be timed to a specific day. Every step in the process could have a large impact on pregnancy success, so each task is done with the utmost care for both the research and the wellbeing of the bison – from freezing and thawing the sperm and embryos, to transferring them to the females, to training and caring for the herd.
This complexity was evident in the first trial where five bison inseminated with either sexed or non-sexed (conventional) sperm were confirmed pregnant by ultrasound 28 days post-insemination. Unfortunately, two of the early fetuses did not survive. A second trial carried out in the bison who were not pregnant involved the transfer of embryos that had been fertilized by sexed or conventional sperm. Unfortunately, the fragile nature of frozen-thawed embryos resulted in no successful pregnancies and highlighted the importance of the continued research.
Your Toronto Zoo is proud to be a part of this collaboration and is excited to support the long-term sustainability of this iconic native species.
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