Twenty lambs have been found dead on a farm in Carterton, thought to have been savaged by dogs.
The lambs, which Prestige Cars owner Robbie Froome bought six weeks ago, were discovered in the nearby river in an horrific state.
"They'd had their guts ripped out," Mr Froome said.
He was notified by his neighbours on Wednesday that 20 of his 40 lambs grazing at his property were dead.
Mr Froome said he believes two or three dogs were responsible for the deaths.
"One dog couldn't do 20 lambs. It had to be two or three dogs to do that many at once," he said.
Mr Froome, a farmer for 17 years, has seen a number of dog attacks but none of such a large number.
"That holds the record for me, for the amount done by a dog," he said.
Mr Froome has contacted the Carterton animal control officer and will be setting up a dog trap, but he said it was difficult to catch the responsible dogs.
"I know from times past it's pretty hard to find them, they get pretty cunning."
Mr Froome said the attack had been costly, with each lamb worth about $50 and time spent burying the animals. "If we can find whoever's dog that did it, we will be giving them a bill for it."
He did not know whether the dogs would have been strays or pets.
"They can just as easily be someone's pet. They do the damage and then go home and nobody is any the wiser.
"If I catch it, I'll be shooting it, as simple as that, which you're quite entitled to do," he said.
Carterton animal control officer Robert Millar said he was unsure where the dogs were from.
"No one saw the dog or knew where it had come from. There haven't been any reports of any stray dogs."
He said even if the dogs were found, it would be hard to prove they were the perpetrators.
"If we found the dogs now, it would be very difficult to tell that they were the dogs that did it unless they were caught in the act.
"The chances of finding the dog and knowing [it was responsible] are pretty slim," Mr Millar said.
No other attacks in the area had been reported.
"It's all a bit out of the blue. Nothing's been reported up there for some time."
Mr Millar said if the dogs entered Mr Froome's property again he could legally shoot them.
"If the dogs come into his property amongst the stock, he has a right to shoot them on sight, and definitely if they are worrying [the sheep]."
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