The same week that President Obama declared the American bison the national mammal, two bison calves made history. They were the first bison ever born through in vitro fertilization and surrogate parenting. They’re part of a program at Colorado State University to create a herd of genetically pure bison that are also free of a deadly disease called brucellosis.

Most of the bison you see today have traces of cattle genes in their genetic make-up but here’s how one smart woman is working to create a herd that, genetically speaking, is as close as possible to the iconic beasts that roamed the plains before European settlers arrived.

Without a backward glance, this bull bounded out of the trailer and charged across the prairie toward his new family of eight females and one male calf.

Jennifer Barfield, Ph.D., lead researcher at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences says, “The ladies were like, who is that handsome man? They came running for him, which is really fun.”

“In their size and their movement they’re really impressive animals,” described Hayley Benham, a grad student at Colorado State College of Veterinary Medicine.

They are an exclusive group of bison from Yellowstone National Park, one of the few places in America you will find genetically pure bison with no trace of cattle genes.

Barfield explained, “You help kind of preserve this line of bison that were more similar to the ones that were here before Europeans arrived. For many people that’s really important to preserve.”

In Barfield’s animal reproduction lab, tanks of liquid nitrogen are home to hundreds of pure bison embryos and sperm samples to be used for artificial insemination and surrogate parenting.

“We can preserve those really valuable genetics, but also, that in doing so we can produce animals that do not have brucellosis,” detailed Barfield.

Brucellosis is a big threat to bison. It’s a contagious bacterial disease that causes abortions. The bacteria almost single-handedly hampered bison conservation efforts. But these bison are safe.

“We incorporate in embryo washing and washing of the sperm as well to ensure that when we create new offspring the disease is not there,” said Barfield.

Already the herd has grown by six calves.

Barfield hopes that as the herd grows it will become a resource to grow other disease-free, genetically pure bison herds. The project costs about $90,000 to put the herd on the grassland on the soapstone prairie west of Fort Collins, Colorado, and $80,000 a year to maintain them, with the funding coming from grants, sponsorships and other fundraising efforts, Barfield said.