Agriculture officials say the region is being stripped of vegetation and is carrying about 1000 more horses than it can support.
Options for reducing numbers are being explored.
Funding have been approved for additional corrals, although there is no indication what the ultimate fate of captured horses will be.
Horse advocates have challenged the agriculture department's position, suggesting the feed situation in the range is not as bad as reported.
Horse adoption programmes have been unable to keep pace with the herd's breeding.