Anytime there is a disease in 50 percent of a herd and it is causing the herd to abort its young, it's imperative to act to eradicate the disease. That also will take care of beef producers' concerns about the spread of brucellosis.
Brucellosis causes bison and beef cattle to abort their calves.
Most infected bison cows abort their first calf and then are able to bear a live calf, says Knight. Experts estimate that up to 50 percent of Yellowstone's bison have the disease. That has prompted several states to require Montana cattle to be tested to prove they are brucellosis-free. The problem is complicated by the size of the Yellowstone bison herd. Hunger is driving bison out of the park.