A CSU researcher bred a disease out of iconic Yellowstone bison so they could come to Colorado
- Colorado Sun
- Sep 29
- 3 min read
Tracy Ross
With the CU football team debuting its new Ralphie mascot, and Utah bison tripping over the Colorado border, and the Colorado General Assembly making shooting the wooly beasts illegal, bison are having a moment.
But a researcher at Colorado State University who has been studying the animal for years figured out how to tinker with the reproductive material of a celebrity herd to bring a key piece of American history to Colorado.
And the work has been so successful that brucellosis-free bison are being sent to other states to help strengthen the overall population of bison in America and to improve the health of prairie landscapes.
Jennifer Barfield is an associate professor in the College of Veterinary Medicine and Biomedical Sciences at CSU. She became interested in bison midwifery after meeting with scientists and land managers from the city of Fort Collins, Larimer County and the U.S. Department of Agriculture who wanted to raise bison directly descended from those in Yellowstone National Park for release on prairie north of the city.
Bison have lived in the Yellowstone area for thousands of years and carry the same traits their American Plains ancestors did before commercial hunters and the U.S. Army nearly wiped them — and the Indigenous peoples who relied on them — out in the 1880s.
By the early 1900s only a couple dozen survived, and the Army set to work rebuilding the Yellowstone herd with bison from private ranches. But in 1910, a nasty disease called brucellosis was identified in U.S. cattle and by 1917, it found its way to bison.
There began decades of the ranching industry and Montana officials trying to eradicate brucellosis from the state, in part by keeping the Yellowstone herd within park boundaries or capturing, testing and killing ones that migrated out.
The herd that exists in Yellowstone today has had little or no integration with other animals such as cattle, says CSU, meaning the bison are most closely associated with the ones that roamed the nation’s grasslands long ago. But there have been concerns about moving them out of the Greater Yellowstone Area because of the potential to spread the disease that can trigger miscarriages and premature births in bison, elk and cattle.
Brucellosis-free bison bred at Colorado State University head onto their new home, Crane Trust, in Nebraska. (Courtesy CSU)
Enter the group wanting to breed brucellosis out of Yellowstone bison, and Barfield, whose interests lie in animal reproduction for conservation and agricultural purposes: “Specifically, I do assisted reproductive technologies, which is a fancy way of saying we help animals get pregnant, establish healthy pregnancies and have healthy offspring,” she said.
In 2011, CSU started a collaboration with USDA to figure out how to use these technologies to “get around” the spread of brucellosis, she added. It involved cleaning sperm and embryos in vitro to get rid of the bacteria that causes the disease. Barfield said that was a major scientific achievement, “because it allowed for the successful breeding of bison directly descended from the Yellowstone herd,” which ranchers and wildlife lovers fear — and don’t want in Colorado.
Barfield’s work also led to CSU establishing a herd of “heritage” bison, the Laramie Foothills Bison Conservation Herd, in partnership with the city of Fort Collins and Larimer County that roams the Soapstone Prairie Natural Area and adjacent Red Mountain Open Space north of Wellington near Fort Collins.
All of this is important, why?
The Laramie Foothills herd is “closed,” which “from a biosecurity standpoint, a disease standpoint, makes it a little more secure,” Barfield said.
Bison are also “ecosystem engineers, meaning their presence on the prairie supports plant and animal communities,” she added.
“I mean, other grazers can do that too, but I think when you think about the integration of people and wildlife, and even livestock and your environment, it’s all interconnected. And where we have our bison, we have cattle ranchers on all sides of us, so having a healthy bison population also benefits the cattle populations that are across the fence.”
A few weeks ago, researchers involved with the project transferred several Laramie Foothills bison to the Crane Trust, a conservation organization that maintains 10,000 acres of critical habitat for cranes and other species in Nebraska, and works closely with indigenous communities in the area.
Many Native American tribes have longstanding spiritual and cultural connections to bison, and CSU has worked closely with the InterTribal Buffalo Council to transfer animals to tribes. Since its founding in 2015, the Laramie Foothills program has donated more than 125 animals to 11 different tribes.
