MINNEAPOLIS — Researchers have transplanted embryos originating from the bison herd at Yellowstone National Park into female bison in Minnesota in hopes of increasing the genetic diversity of herds in the state and helping to restore America's official mammal to the landscape.
While Yellowstone bison are prized because they're free of domestic cattle genes, experts say using them in breeding programs is difficult because they carry a contagious disease called brucellosis, which causes spontaneous abortions in pregnant cattle. Other efforts at spreading the genes of Yellowstone bison have focused on using animals descended from the park's herd that have been certified as disease free. Transplanting embryos uses in-vitro fertilization to get around the problem.
Colorado State University animal reproduction professor Jennifer Barfield and other researchers last month implanted embryos in four female bison at the Minnesota Zoo. Veterinarians will conduct ultrasound tests in the coming months to see if the animals became pregnant. If all goes well, they'll give birth to baby bison in the spring.
The four females are part of a larger "conservation herd" managed by the zoo and the Minnesota Department of Natural Resources, which also includes bison at Minneopa State Park and Blue Mounds State Park that are largely free of cattle genes. The herd would benefit greatly from Yellowstone genetics, officials said, but securing a sexually mature Yellowstone bull to breed conventionally has been impossible because they can't be moved out of the park.
"It will also demonstrate that we can use reproductive technologies to move the Yellowstone genetics outside of the park without the threat of spreading the disease brucellosis, which has implications for bison conservation on a broader scale," Barfield said.
Tens of millions of bison once roamed the Great Plains but were hunted to near extinction in the late 1800s. About 30,000 wild bison now roam the country. Yellowstone has the largest population so its genetics are highly diverse. While commercial bison herds now number more than 300,000, many of those animals and other wild bison are bison-cattle hybrids to varying degrees. Government, tribal and zoo efforts seek to restore the animals' original genetics.
This isn't the first time embryo transfers have been used to improve the genetics of bison herds. Barfield also led transplants that resulted in a calf with pure Yellowstone bloodlines at New York's Bronx Zoo in 2012. For both zoos she took eggs from female bison that had been culled from the Yellowstone herd and fertilized them with sperm from males in Colorado State's herd. And she has produced several other calves at the university via embryo transfers and artificial insemination. She's also waiting for ultrasound results to see if other recent transfers worked at Colorado State and the Bronx Zoo.
But the process is still "an experimental procedure at best," cautioned Keith Aune, bison program director for the Wildlife Conservation Society, which runs the Bronx Zoo. The technique produced only one calf in about 25 tries at the Bronx Zoo, he said, but the field of bison research is young and the approach may become more successful with more development.
Aune, who's not directly involved in the Minnesota project, said Barfield's work fits well into the bigger picture of bison conservation. He said the Toronto Zoo is also experimenting with embryo transplants in a northern subspecies called the wood bison. He said the Bronx Zoo plans to import several bison with pure Yellowstone roots from a disease-free herd next month if it gets the necessary permits.