The lawsuit sought to compel the Montana Department of Livestock to restrict bison from roaming outside the Yellowstone National Park boundaries in the late spring and early summer. The fear from the Stockgrowers: that roaming bison would somehow transmit brucellosis to cattle in grazing areas later in the summer. There’s never been a documented case of bison transmitting brucellosis, a disease that causes pregnant cows to sometimes spontaneously abort their fetuses, to cattle; experts peg elk as being more likely to transmit the disease to cattle. Brucellosis is a serious issue for the cattlemen: besides the loss of potential stock, the presence of brucellosis means cattle must undergo testing before being shipped out of state.
Much of the existing bison-management plan is built around the prevention of brucellosis, however. In the late spring bison are hazed back into Yellowstone National Park or, in years past, slaughtered.