American bison –- recently named the U.S. National Mammal – were nearly hunted to extinction during the 1800s and most of those that survive today are hybrid species that have been bred with cattle.  However, tucked away in Utah's Henry Mountains, an isolated population of roughly 350 genetically pure, disease-free American plains bison roam freely, researchers have revealed. This discovery opens new doors for improved animal conservation. 

"This is a remarkable finding considering these free-roaming, legally hunted animals live on unfenced public lands and graze alongside livestock," Johan du Toit, one of the study researchers and wildlife ecologist from Utah State University (USU), said in a news release.

For their study of these rare bison, researchers from USU and Texas A&M University (TAMU) analyzed genetic samples from 129 individual animals to learn more about the ancestry of the Henry Mountains herd. Their findings confirm the animals recently found in the remote high-altitude oasis of southeastern Utah are direct descendants of 20 Yellowstone National Park bison originally relocated to the area in the 1940s. This means they have not been crossbred with cattle. 

During the 19th Century, bison were crossbred with domestic cattle in hopes farmers could create livestock with the most favorable characteristics of each species. At the same time, pure-bred bison were nearly wiped out. The Henry Mountains herd, along with bison herds in Wyoming's Yellowstone National Park and Wind Cave National Park, are the only conservation herds of American bison free of detectable levels of cattle DNA, researchers say. 

"The idea was to breed livestock with the hardy, drought-resistant traits of the bison and the more docile nature of cattle," du Toit explained. 

Generally speaking, bison-cattle hybridization was accomplished in managed settings. However, it was widely believed that if bison and cattle were allowed to graze together they would mate and naturally crossbreed. The recent study, on the other hand, disputes this belief because the Henry Mountains herd has roamed freely among cattle for more than 70 years.

"Given a choice, a bison bull shows no interest in domestic cows," du Toit said.

This has significant implications for conservation because it shows bison and cattle can roam the same area and share food resources, all while avoiding crossbreeding. Furthermore, researchers noted the Henry Mountains herd is free of brucellosis, which is a highly contagious bacterial disease that affects bison, cattle, elk, dogs and even humans. 

"The Henry Mountains bison are the only demonstrated genetically pure, disease-free and free-ranging bison population left in North America," du Toit concluded. "They're consequently an extremely important resource for restoring the United States' iconic national mammal to more of its former range."

Their study was recently published in the journal PLOS ONE.

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