BILLINGS, Mont. -

The head of the Montana Department of Livestock says his agency will only allow the expansion of a bison tolerance zone around Yellowstone National Park if the population goes down.
    
The Board of Livestock meets Monday and Tuesday. The Billings Gazette (bit.ly/1t1n0w3) reports the board will consider a plan that would allow bison to roam more freely outside the park's west side.
    
The board rejected the initial proposal in March, saying they wanted more details and comments from the cattle industry.
    
DOL Executive Director Christian Mackay told the Environmental Quality Council Thursday the agency will allow expansion of the tolerance zone if the bison population is 3,300 or less.
    
The park's bison population reached 4,600 last year. Since then, about 630 bison have been killed or transported to testing programs.