Police in Kaipara are investigating the slaughter and theft of two cows - one where the legs were hacked off a pregnant cow and its body left in a paddock.

While it is unclear if the two incidents were linked, both are believed to have happened last Wednesday night.

At a Waiotira farm, 32km south west of Whangarei, just a piles of internal organs remained.

One of the farm's owners said the two-year-old Angus heifer was taken from a paddock close to the road.

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She said it happened around midnight when the cattle were sleeping by the fence. She thought the heifer, which was in a paddock with about 25 to 30 other animals, had probably been shot.

The owner said there were some drag marks in the grass where it looked as if the animal had been dragged through the gate and loaded into a vehicle.

She thought it would have taken four people to lift the carcass.

The owner said the cow would have been worth around $1000 and was very good meat.

She said it had been recently drenched so wasn't currently fit for human consumption.

Further north, police confirmed a second cow, around five years old, had been killed in Waipoua River Rd sometime between 10pm on September 13 and 6am the next day.

A Facebook post contained graphic pictures of the slaughtered cow with its legs hacked off and the body left in a paddock.

The post said the cow was pregnant and due to calve anytime and "the calf inside her was killed viciously as well".