Scenes from an earlier Kaimanawa muster. More homes are needed for horses being mustered later this month.
Jenks said if the number of suitable homes fell short, the muster number would be at the lower end of the range.
"It all depends on how many horses we can place."
If more homes were available, a higher number would be pulled from the central North Island ranges.
He said drought conditions and the economic downturn had thus far resulted in fewer adoption applications than expected, but they did tend to come in faster as muster time approached.
He urged anyone interested in adopting a Kaimanawa horse to put in their application as soon as possible, as homes needed to be checked and locked in before the muster.
"There are no second chances," he said.
"This week will be the deciding week."
The muster is scheduled to take place on the first day with appropriate weather from May 26.
The biggest factor likely to cause up a hold-up was wind, he said.
Last year, the Department of Conservation set out to reduce the wild herd from 500 to 300. In total, 230 horses were pulled from the wild.
Jenks said if 120 horses were mustered this year, the trust would expect a breakdown of roughly a third of older males (three years and older), a third mares and a third foals and yearlings.
"What we have always guaranteed," he said, "is that we will never see a foal or yearling go to slaughter."
The horses had come from a drought-affected area that had not been mustered for three or four years, and this may have affected the sex and age distribution of the mustered horses, he said.
The wild herds were across five different areas and the muster tended to focus on two different areas each year.
The trust aimed to find homes for all the young stock - or where necessary undertake that work itself to make the horses more readily adoptable - and some of the mares.
Nearly all the males three years and older will go slaughter within 24 hours of the muster to minimise the stress on them, although the odd one may be found a home.
He said bringing on the young stock proved costly for the trust - at $1000 to $1200 a horse.
"We may well have to do it this year. It's an expensive way of doing things."
Jenks said the five-year working plan for the wild horses had aimed at a reduction from 500 horses to 300 horses for two main reasons - the amount of grazing land available was being reduced by 1000 hectares a year because of regenerating manuka, and to keep down the cost of the muster, running at about $120,000 a year.
The trust supported long-term contraceptive measures and had been talking to the Department of Conservation about the option.
Interested parties were following a four-year trial of a long-term contraceptive on wild horses in the United States, which is half-way through.
The new drug requires only one injection (an earlier option required two) and evidence to date suggested it could be used on pregnant mares without damaging the foals.
Research indicated very low conception rates in the first year after use, with the chances of conception increasing in each of the following two or three years.
Jenks said a successful muster this year would mean one would not be held in 2011. It was possible long-term contraceptive measures might be available for use in the 2012 muster.
Significantly, the trust had rehomed 63 Kaimanawa horses in the last year which had been collected in musters going back as far as 1997.
Early adoptions, organised through the Department of Conservation, had less stringent requirements than those used by the trust today.
Many individuals with a "kind heart and a bit of land" had offered horses homes and, with drought and harder economic times, it had not worked out for some.
Those interested in adopting a horse can download an application form from the trust's website.
Applicants need to provide the names of two referees and are required to pay $100. Their facilities will be checked to ensure they are suitable.
Jenks said the $100 would be credited against the $200 cost for a horse. Subsequent horses are $175 each.
He said the $100 charge was non-refundable if the home offered proved unsuitable. The charge was introduced to reduce the chances of the trust incurring the cost of checking possible homes around the North Island, only to find them unsuitable.
Anyone unable to take a horse can make a donation to the trust (see address below), which will go toward saving horses.
Donations can be sent to
PO Box 133