Agencies to let more bison outside Yellowstone State and federal officials say they've tentatively agreed to allow more bison to roam outside Yellowstone National Park without being captured and slaughtered to protect cattle against disease. The plan, which remains in draft form, would allow an unlimited number of bison to stay during winter in an area west of Yellowstone known as Horse Butte. The animals would not have to be tested for brucellosis, a disease carried by bison and feared by ranchers because it causes cattle to abort their calves. Last year, more than 1,600 bison leaving the park were killed to guard against the disease. Final adoption of the plan is expected next month in Helena, when five federal and state agencies wrap up a series of meetings they've held on the issue over the last several months.