The SPCA and experienced horse people met at the property yesterday to assess and try to remove as many of the animals as possible.
One of the horses at the South Auckland property.
"We were able to rehome three of them to an excellent horses handler," she said. "These three have a chance ... we were able to catch and handle them."
The other horses proved too difficult to catch and the animals were becoming stressed after three or four hours of attempts.
"I want to stress that we had very experienced horse handlers with us," she said.
"They are better off being euthanized.
"I have had a lot of people contacting me, saying they can do this, or they can do that, which is awesome.
"But the reality is with these horses ... it's just not happening. Why stress them out?"
Euthanizing was the best option, she said.
"I don't think it's necessary to put them through any more stress. They are better off in heaven."
"It's a hard decision, but I have made it in consultation with the vet."
She also discussed it with the horse handlers who saw the horses.
The horses, she said, had experienced little human contact. "The only human contact was a bit of hay over the fence. They have not even been out of the paddock they have been in."
She said she realised some people would voice disapproval of the decision, but she was satisfied it was the right decision. "I stand firmly by that decision," she said. "These calls have to be made.
"I had a gentleman [with me] who had broken in many a horse. He agreed. He was pushed around. It was dangerous for us yesterday," she said.
She said the unhandled horses were in urgent need of hoof and dental care, and had low body scores.
The horses were being well fed in the meantime and she would organise their euthanasia within the next few days. "It will be done humanely and quickly. There will be no pain or distress," she said.
She said she would return to the property today and would see if any more horses could be caught. "I don't hold out much hope."
In total, seven horses have been successfully removed from the property. The SPCA is caring for two mares and their three-week-old foals at its Westney Road, Mangere, premises. Feed donations were sought and the SPCA was grateful to those who have responded to the appeal.
The three rehomed yesterday were two yearlings and a mare.
The SPCA became aware of the situation at the 10ha (25-acre) property a week ago. A group has been visiting the property daily to feed out.
The owner signed all the horses over to the SPCA on Monday.