New breeding method may augment bison herd

New breeding method may augment bison herd

Minnesota Zoo and Colorado State University use new embryo transfer breeding method to preserve Yellowstone bison genetics.

Four female bison at the Minnesota Zoo may give birth this spring to calves fathered by bison from Yellowstone National Park following the successful transfer of embryos to the females earlier this fall.

Researchers from Colorado State University (CSU) used a new breeding method with the potential to expand the genetic diversity of bison herds in Minnesota and across the country. The four females are part of the Minnesota Bison Conservation Herd that are collaboratively managed by the Minnesota Zoo and the Minnesota Department of Natural Resources (DNR).

Photo: Minnesota Department of Natural Resources.

In September, the Minnesota Zoo partnered with Dr. Jennifer Barfield and others at CSU to transfer embryos into four bison cows at the zoo using embryos generated from bison originating in Yellowstone National Park. These embryos were created using in vitro fertilization in a lab at CSU and were frozen for storage.

With the assistance of Dr. Greg Farrand, a large-animal veterinarian from Colorado, Barfield successfully implanted the embryos on site at the Minnesota Zoo. An ultrasound will be conducted in the coming months to confirm if the animals became pregnant after the embryo transfers and that the pregnancies are on track for successful births next spring.

"I am very pleased with how smoothly the embryo transfers went," Barfield said. "While a new calf with valuable Yellowstone genetics would help augment the genetics of the Minnesota herd, 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."

"We are excited about this partnership with CSU and are very hopeful that this will work and that we can finally add valuable Yellowstone bison genetics to our Minnesota Bison Conservation Herd," Tony Fisher, director of animal collections for the Minnesota Zoo, said.

Yellowstone bison genetics are not well-represented in the Minnesota Bison Conservation Herd and are extremely desirable for increasing the herd's genetic diversity. However, because of a transfer moratorium, it is not possible to obtain a sexually mature bull for natural breeding. The moratorium was established because bison in Yellowstone have a high probability of carrying a contagious bovine disease known as brucellosis that causes spontaneous abortions in pregnant females. The frozen embryos from Yellowstone were carefully treated prior to the transfer to prevent any chance of transmitting this disease.

"Bison from Yellowstone National Park are some of the only American plains bison that have survived on their own in nature without humans guiding breeding," added Molley Tranel Nelson, regional resource manager for Minnesota State Parks & Trails. "Free of cattle genes and selective breeding programs, they are one of the few bison herds where natural forces have continually shaped their genetics. They are incredibly valuable to the diversity of the Minnesota Bison Conservation Herd."

At one time, bison herds in North America were estimated to number 30-60 million animals, and they roamed throughout all but the northeastern portion of Minnesota. During the late 19th century, bison were hunted almost to extinction, until fewer than 1,000 animals remained in the entire U.S. The last wild bison observed in Minnesota was in Norman County in 1880.

During the remarkable comeback of North America's largest land mammal, a silent genetic threat was introduced. Domestic cattle were allowed to interbreed with many of the protected herds, contaminating and changing the character of the American plains bison genome. It is estimated that less than 1% of the world's remaining American plains bison have tested free of cattle genes.

The Minnesota DNR reintroduced bison into Blue Mounds State Park in 1961, and genetic testing from 2011 to 2013 found that they were largely free of any genetic material that would have come from crossbreeding with cattle, making them rare.

In the fall of 2015, the Minnesota Zoo and DNR released 11 bison at Minneopa State Park — three females from the zoo and eight females from Blue Mounds State Park — to start a bison herd near Mankato, Minn. The Minnesota Zoo will continue to partner with DNR to release more zoo-born bison that have tested free of cattle genes into Blue Mounds State Park and Minneopa State Park in an effort to increase the Minnesota Bison Conservation Herd to 500 animals.

The mission of the Minnesota Zoo is to connect people, animals and the natural world to save wildlife. For more information, visit

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