Yellowstone Bison Genes Transferred To Minnesota Herd

A new collaboration between Colorado State University and the Minnesota Zoo aims to get Yellowstone bison genes circulating in a new herd.

According to the Billings Gazette, using ovaries obtained from a slaughterhouse, CSU professor Jennifer Barfield has transplanted fertilized embryos into four bison cows from the Minnesota Bison Conservation Herd at the Minnesota Zoo. Barfield and the Zoo are waiting to see whether the cows will give birth this spring—a feat that would replicate some of Barfield’s earlier success with getting Yellowstone genes in other bison. From the Gazette:

Barfield began her research in 2011, basing the techniques on those used for the cattle industry — which is an odd coincidence considering that bison first contracted the disease brucellosis from cattle, a disease that has since caused numerous problems for cattle ranchers near Yellowstone National Park.

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, or APHIS, retains a small herd of Yellowstone bison outside of Gardiner for scientific study. By extracting live embryos from those bison cows, a technique that does not require surgery, Barfield successfully transplanted an egg into a Bronx Zoo bison in New York City.

That first calf was born in 2012. Barfield has an ultrasound photo of the now 3-year-old male on her desk, as well as a photo of him as an embryo — reminders of how far the research has come.

After that first success, the program has grown to include the successful birth of 10 bison in a conservation herd of 16 bison kept at Fort Collins, Colo. At the Bronx Zoo another six bison cows have received Yellowstone embryos.

“We’ve continued to work on the procedure and increase our success rate,” Barfield said.

The work has been yet another tie between the Bronx Zoo and bison. The zoo’s Wildlife Conservation Society was instrumental in preserving bison in the early 1900s.

As part of the transplant process, Barfield’s lab scrubs the embryos of brucella abortus bacteria; the bacteria causes brucellosis, a much-maligned cattle disease somewhat prevalent in Yellowstone’s bison herd. Many regulations bar the spread of brucellosis, which can cause abortions in cattle. One such regulation mandates the culling and slaughter of Yellowstone bison under the Interagency Bison Management Plan.

While cattle ranchers fear the spread of brucellosis to their herds from bison, there have been no documented cases of transmission between bison and cattle. Elk, which also carry brucellosis, are far more likely to spread the disease through bacteria left in birth material such as placenta.

Barfield stresses her work does not substitute or overshadow efforts to keep the Yellowstone herd wild and viable. Nonetheless, she says the possibility of the Yellowstone herd one day becoming brucellosis-free is unlikely—unless something happens with the elk. From the Gazette:

Barfield said preserving and spreading the Yellowstone bison genetics does not dilute the value of the existing Yellowstone herd, nor would the technology ever be used to remove Yellowstone’s bison and reintroduce bison free of brucellosis.

“That’s absolutely not feasible and not something we would want to do,” she said.

Besides, even if bison with brucellosis were removed from the park elk would still carry and be able to transmit the disease.

“It’s not a strategy that would work because of the problems involved,” Barfield said.

Yet if a vaccine were ever developed to wipe out brucellosis in Yellowstone bison and make Barfield’s work obsolete, she said she wouldn’t care.

“I’d be happy to work myself out of a job,” she said.

Bison have a long history in North America, once numbering in the millions before being driven to near-extinction in the 1800s by overhunting and wanton sport shooting. Today, “genetically pure” bison are a rarity, according to a Minnesota Zoo press release:

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, obtaining a sexually mature bull to breed naturally has been impossible. 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.


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 one percent of the world’s remaining American plains bison have tested free of cattle genes. The DNR reintroduced bison into Blue Mounds State Park near Luverne, MN in 1961, and genetic testing from 2011-2013 found they were largely free of any genetic material that would have come from cross-breeding with cattle, making them rare.

In the fall of 2015, the Minnesota Zoo and DNR released eleven 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. The Minnesota Zoo will continue to partner with the 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.

About Sean Reichard

Sean Reichard is the editor of Yellowstone Insider and author of Yellowstone Insider For Families 2017.

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