As of last week the person/s responsible for shooting the mare had not been identified, and no witnesses had come forward with any further information.
"Fortunately, the foal is being cared for by a very generous foster family, and is doing well," Ms Knowler said.
"We would like to thank this family for helping. The foal's survival is the only positive part of this case."
The mare is believed to be only one of several shot over recent weeks. A second foal, believed to have been hours old when it was found, is also being fostered, while a third died, probably of starvation. It is not believed to have been shot.
Aupouri horses have been shot in the past, often, apparently, as a source of dog tucker, but the animals killed over recent weeks were not butchered.
Summit Forests requires that everyone who wishes to enter the forest obtains a permit to do so, and prohibits the carrying of rifles inside the forest.
Meanwhile, Ms Knowler urged anyone who knowledge about the shooting of horses in the forest, or those involved, to contact her on (021) 268-6920 as soon as possible.
"We appreciate all reports of animal cruelty in our community, and encourage the public to call us immediately if they ever have concerns about an animal's welfare," she added.
* The NZ Forest Service actively protected the feral horses in Aupouri Forest, a practice that has continued, most recently by Summit Forests. The horses are regarded as a tourist attraction and are often seen in small herds, in the forest and on Ninety Mile Beach.