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He wants the owners of the canine to come forward and surrender it to authorities before it embarks on another killing rampage in the Ngunguru Ford Rd area, north east of Whangārei.
Galpin was devastated to find that nearly half his 76-strong flock of romney/south suffolk cross sheep had either their "throats ripped out or their faces caved in" while others drowned in a creek as they tried to flee their attacker.
When the ewes and lambs started bunching up in a corner last Thursday about 6.30pm Galpin knew something was up.
"My first thought was it was a dog chasing them," he said.
"There was one dead and then I found another one with its head crushed in. I thought I had got off lightly."
He recalls a blood splattered dog emerging from the bush and described it as a bull mastiff with a white face and brindle body.
On Friday, Galpin reported the attack to dog control authorities.
But it was on Saturday when he received a call from a neighbour who had reports of dead sheep in the creek area of the property.
As the sheep tried to outrun their attacker they had run through scrub and gorse and plunged into a river.
Others lay near the steam with their throats ripped out while about six were found huddled together on a ledge above the stream.
"It's totally disheartening. I go through the procedures of making sure they don't get flystrike, I drench them and watch them grow. Then all of a sudden there is no investment and there are people denying it's their dog."
He has since had to shoot one more lamb as it was unable to eat with a damaged jaw, and, he reckons another one will have to be shot for the same reason.
The fatalities have hit Galpin in the pocket to the tune of $3000 at least. He was about to shear them as well so he also lost out on any money he could have made through the fleeces.
Animal control officers went on Friday to the property where the dog is believed to have roamed from but were unable to locate it. Investigations are continuing.