A congenital defect combined with U.S. government plans to kill bison exposed to an infectious cattle disease could doom America’s last wild herd of pure-bred buffalo at Yellowstone National Park, a genetics expert said in a new study.

The findings were posted on Monday in Nature Precedings, an online archive for pre-publication research by scientists, as the government and environmental groups clashed in court over an icon of Western wildlife that dates to prehistoric times.

Government managers continue to corral hundreds of bison whose search for food has led them to stray from Yellowstone into nearby Montana grazing lands.