Four-year-old Braith Kalin made the grisly' />

A sadist who chopped off the head of a little boy's pet lamb is being sought by south Taranaki police.

Four-year-old Braith Kalin made the grisly discovery when he went out with his father Jason to feed the animal on the family's Eltham property on Tuesday.

Braith noticed the six-month-old lamb wasn't running around on its chain, the Taranaki Daily News reported.

"Dad, why has Shaun go no head? he asked his father.

The lamb's head was missing - it was believed the killer had wrapped it in a towel taken from the clothesline.

"Who could do such a sadistic thing?" Braith's mother Mandy Kalin asked.

Mrs Kalin said the children had been petrified by the incident.

"If the lamb had been killed for the meat...I could possibly understand it, but not this. It's not something a normal, straight person would ever do."

Mr Kalin told police he suspected someone with a grudge may be to blame.