The Department of Conservation says it makes financial sense to permanently reduce the number of wild horses in the Kaimanawa ranges.
The horse population has been kept at about 500 for the last ten years, but an advisory board has decided to reduce that number to 300.
DoC area manager Jason Roxburgh says annual musters are time-consuming and cost the department up to $120,000, money which it would like to use for environmental projects with a higher priority.
Mr Roxburgh says between 150 and 180 horses will be collected in the next muster, and homes will be found as many as possible.
The two organisations which re-house mustered horses say very few applications have been received from potential owners.
They say unless homes can be found for the horses collected in this year's unusually big muster, they will have to be culled.
SPCA Auckland chief executive Bob Kerridge says the real Kaimanawa horses have already been decimated by culling.
He predicts that eventually there will be no herd at all, and believes that is what the Department of Conservation wants.