BILLINGS, Mont. (AP) -- A state official says livestock agents on horseback and in a helicopter have hazed about 350 wild bison into Yellowstone National Park as part of the annual drive to get the animals out of Montana to make way for cattle.

Department of Livestock spokesman Steve Merritt said Wednesday all remaining bison outside the park would be driven into Yellowstone Thursday or soon after.

Yellowstone spokesman Dan Hottle says the park will next push the animals several miles past the state line. That's so they don't return to Montana, where thousands of bison have been killed to guard against the disease brucellosis.

About 500 bison were in the West Yellowstone area earlier this week.

A pending lawsuit from environmentalists seeks to stop the use of a helicopter in the bison drive.

Copyright 2011 The AP.