In June, 1997, the National Research Council began a study regarding the threat to cattle by Yellowstone's bison herd. Scientists determined that the cause of the threat is brucellosis, a chronic bacterial disease that can cause cattle and bison to abort their calves.

A meeting was held regarding bison ecology and management also during June. A veterinarian from the Department of Interior's National Wildlife Health Center in Bozeman, Montana, Thomas J. Roffe reported that one-fifth of the female bison in Yellowstone appear to be infected.

In past studies it has been recorded that half of the park's bison tested positive for antibodies to bacterium Brucella abortus with standard cattle blood tests. The tests, however, can't distinguish between those that have an active virus and those who were exposed and those who fought the virus off.

Roffe and a team of scientists from state and federal governments spent many days in the snow dissecting the lymphnodes and reproductive tissue from the carcasses of female bison who had been shot in an effort to prevent the spread of the virus after they wandered out of the park.

Eight out of twenty of the cultures taken tested positive for antibodies. This figure suggests that 20 % of the females carry the bacterium.

The study is concentrated on the females because the bacterium is believed to be spread from leftover birthing tissue after a calf is born or aborted on the range.

The scientists consider this finding only a small piece of the puzzle as to whether Yellowstone's bison are a significant threat to cattle living in the vicinity of the range. It is still a question regarding what fraction of the bison are infectious at a particular time.

Roffe is in favor of research being executed on how to minimize the threat of bison infecting cattle, rather than research based on the exact risk the bison are to neighboring cattle. Roffe and his team have taken a step towards this research by radio collaring 60 female bison who will be followed over the next five years.