Researchers break new ground with in vitro fertilization and the transferring of frozen embryos in bison
Four healthy Wood bison calves bouncing about in a pasture near Saskatoon marks a big step forward in reviving the species’ population.
Storm, Moon, Hope and Fridge are the world’s first successfully produced bison calves using in vitro fertilization.
“That is an amazing feat, and it’s taken a long time to get to this point,” Gregg Adams of the University of Saskatchewan’s Western College of Veterinary Medicine said during a recent field day in Saskatoon.
He said the college started the Wood Bison Reproduction Research Project nine years ago and produced Storm, Moon and Hope in Petri dishes by joining bison eggs and sperm. The resulting embryos were then transplanted into surrogate bison cows more than nine months ago, which gave birth to the three calves in July.
Fridge was aptly named after being produced from a frozen embryo that was taken from a bison cow in 2012 and then transferred to a surrogate mother last year. This process was also another reproductive first for the bison species.
Adams said reproductive technology biologists started at ground zero and knew nothing about bison’s normal reproductive pattern.
“We didn’t know what their ester cycle was, we didn’t know when they came into heat, when they ovulated,” he said.
“These bison in Canadian latitudes are very, very distinctly seasonal. That means that they only have a breeding season very distinctly around the first of September for a couple of months. The rest of the months of the year the females don’t cycle.”
The ability to turn eggs into embryos has significantly improved over the course of the program from the initial IVF success rate of seven percent.
“Forty-five to 50 percent of the eggs that we put in culture and fertilize in vitro now produce babies, which is equivalent to the efficiency in domestic livestock, cattle,” said Adams.
“We are now able to collect on average about seven eggs per collection attempt. We’re able to do this from live animals, mature those eggs in a lab, put them together with the semen that we’ve collected from our own bull here. That semen was frozen.”
Cryopreservation techniques with bison semen are another major hurdle that researchers continue to develop.
The systematic destruction of bison combined with harsh winters during the late 1800s decimated both the prairie and woodland species.
“The die-off was so bad that all the bison we have today are derived from less than 200 at the turn of that century,” said Adams.
Between 5,000 and 7,000 wood bison now remain in the wild, which is less than five percent of the original population.
“That’s a tremendous bottleneck, and to recover from that is a real tribute actually to the toughness of this species,” he said.
As well, initial conservation efforts from more than 80 years ago that crossed bison and cattle infected the animals with brucellosis and tuberculosis.
Canada’s domestic livestock population is now free of brucellosis and tuberculosis, but 30 to 60 percent of wild bison are infected with both diseases, which has hampered their population growth and isolated them from moving out of the parkland regions.
Researchers can use advanced reproduction techniques such as artificial insemination, superovulation and in vitro fertilization to disinfect the egg and sperm, which minimizes the spread of disease and prevents calves from being born with diseases.
“I think what we’re doing with advanced reproductive technologies is really designed to preserve the genetic diversity (of the animals),” said Adams.
Benefits of the technologies also apply to bison producers who want to use Plains and Wood bison crosses for hybrid vigour.
“They will grow faster, be less susceptible to disease, and that’s advantageous to the bison industry,” he said.
Adams said the college plans to produce 200 calves over the next three years. Surrogate herds will need to be identified using bison producers or bison from national parks.
“We can use their (bison producers) animals on their place as surrogate moms, whether they’re Plains bison, Wood bison, or mixed,” he said.
“From a production point of view, we can produce semen, they can ship semen all over so they don’t have to actually ship the bulls that they want and so they can do artificial insemination using bulls in the same way that embryos can be done.… It also allows them (bison producers) to select the genetics that they want and they need, which they otherwise wouldn’t be able to do.”