Matilda is recovering after being attacked in a field near Preston, Lancashire, but her son, Lucas, suffered similar wounds and did not survive.
Seven years ago she was rescued by Khrystinea Farnworth, 24, and her family after they learned that she was being tethered up to a tree with barbed wire.
Shortly after arriving at their farm in Lea Town, Matilda gave birth to Lucas and both looked destined to live their days out with other Shetland ponies and rescue horses out of harm’s way.
But in the early hours of Sunday onwards someone broke open the gates to the field in Darkinson Lane and inflicted slash wounds to the neck and hind areas of Matilda, 24, and Lucas, seven.
Some of the family’s other seven Shetlands received lesser injuries while it appeared a stallion, who acts as a companion to them, was herded into a different enclosure by the offender or offenders.
Police have warned horse owners in the area to be vigilant.
Miss Farnworth said: “It’s disgusting and barbaric. You don’t expect it to happen to you. I still can’t process what has actually happened.
“We are in the middle of nowhere and have no enemies.”
She said she dashed to the field after receiving a phone call from the nearby village pub to tell her that three ponies were loose and outside the premises.
She said: “Lucas was lying motionless in the field. I have gone running up to him and the first thing I saw was a stab wound to the side of his neck. I started crying, I didn’t know what to do.
“I don’t think the slash wounds killed him. I think he has panicked and had a heart attack.
“My niece tracked down Matilda and she also had a massive gash to the side of her neck.”
Matilda, who already had neck scars from her earlier barbed wire ordeal, is recovering at the farm from her injuries, said Miss Farnworth.
She added: “She has lost her son. She is an older pony and she is exhausted, She has had her trust broken by a human again.
“She knows she has lost him. She keeps shouting for him, she keeps whinnying. It’s upsetting.
“They are all pets. They are our lives. They can’t speak, they can’t defend themselves, that is why we have so many rescue horses. We give them a voice.
“I don’t understand people’ s mentality to be able to do that.”
Miss Farnworth said she believed the attack was carried out by more than one person.
“It looks as if our stallion Prince has been herded away from the Shetland ponies,” she said. “If you get a kick from a horse you can be dead, if you get one from a Shetland pony you will just have a bruise.
“Someone has got hold of them to do it. Horses are flight animals.”
On Facebook, Preston Police said: “The incident occurred some time after the early hours to midday today (Sunday).
“This appears to be a deliberate attack which has caused great distress, not only to the owner but the animals themselves.
“We are requesting equine owners to be vigilant and report any suspicious activity to us.
“Anybody with any information that can assist with this investigation can email Pc Magee at [email protected] and quote log reference LC-20170820-0693.”