"They've run this horse down and smashed its back legs," Clapperton said.
The horses were well-known to locals and some people had hunted them "for fun".
However, the behaviour should not be treated as a joke or a bit of fun.
She said it was an "absolutely disgusting" example of animal cruelty "at its worst".
Kaitangata Wild Horse Committee member Rex Robson was alerted to the injured horse in the forestry blocks in the back hills of Kaitangata about midnight in the last week of February.
He visited the site where the injured horse was found and saw the "bone was hanging out".
The 2-year old colt was in terrible condition.
There was no way it could have been treated by a vet and the only option was to put it down.
Robson said locals knew who was responsible and were not happy.
He was aware people had hunted or shot the feral horses in the past but not for "a few years now".
This latest incident was unusual and not something he had seen before.
He understood a complaint about the alleged animal cruelty may be made to the police by the Wild Horses Committee.
The horses are descendants of the former McCrostie estate herd and had roamed the hills around Kaitangata for almost 100 years.
Sergeant Martin Bull, of Balclutha, said the police had not been notified about the incident.
If the injuries inflicted were deliberate, then police were able to prosecute under the Animal Welfare Act.
A person could face up to 12 months' jail time or a fine of up to $50,000 if found guilty.
Sgt Bull said if the incident was believed to be deliberate, then the police should be notified so further action could be taken.
