More than 200 Kaimanawa horses could be sent to slaughter following this year's muster.
This year is expected to be one of the largest wild horse culls on record, with about 300 animals being mustered from the Waiouru Military Training Area.
The muster is carried out every two years, organised by the Department of Conservation and Kaimanawa Heritage Horses.
About 600 Kaimanawa horses are currently in the wild, but there should only be about 300 animals in order to protect the fragile ecosystem and the health of the horses.
The unique tussock grassland where the horses roam contains threatened plants, including at least 16 species in the New Zealand threat classification system.
In 2016 only 100 horses were mustered.
Simone Frewin from Kaimanawa Heritage Horses said this year it would be about 300.
"This is really quite unprecedented. Previously when large numbers of horses were removed it was as much of a welfare issue than anything because the horses were in such poor condition.
"The reason why we're removing so many this time is because the horses are in such great condition that breeding rates have increased to 30 percent per annum and the population is just far too successful."
So far there are 56 applications to re-home horses.
"Even some of those homes may not come to fruition because when we do our home checks we may find that facilities aren't suitable, that sort of thing.
"It's a really dire situation for the horses this time round."
Kaimanawa Heritage Horses is meeting with the advisory group on Friday to discuss options, which might include mustering fewer horses.
Ms Frewin said they were trying not to send large numbers of horses to the abbatoir, but it was a tough job re-homing 300 wild horses at one time.
"As much as we'd love to accept every home that is offered, you just can't do that ... you can't put horses or people into a bad situation.
"It pains us to turn the odd applicant down ... but we just don't have an alternative."
Applications to re-home a Kaimanawa horse close on 1 April.