The stolen rams were worth up to $1100 each.
Mr Powdrell had caught two people red-handed on his own property, while another arrest was made at a neighbour's when a rustler slaughtered a cattle beast on the property.
"We have had some success but farmers have got to take all practical steps they can, [such as] locking gates, installing cameras, and on top of that have really good rural support groups."
Illicit cannabis crops were another problem for Western Bay farmers.
"Cannabis growers go to quite a lot of trouble to access remote areas on people's farms so often you don't even know they're there." No matter how small the offence, it was crucial to report it, he said.
"[Police] are putting together a picture of events and trying to localise where the hot spots are, so they actually do want to know."
Western Bay of Plenty police acting area commander Inspector Karl Wright-St Clair said that in past years an increasing number of quad bikes and petrol thefts had been reported as cannabis growing season got under way.
"Obviously, people need to make sure that type of equipment is secure and put away at night. We would ask that people in rural areas pay attention to any suspicious activity."
Mr Wright-St Clair said rural residents should be aware of unfamiliar vehicles parked in remote areas, people carrying tools and other equipment that could be used to grow cannabis, and people entering remote bush or rural areas.
Cannabis was often grown among maize crops and in remote bush locations in the Western Bay, he said.
Farmers around the country are being urged to be vigilant and report any thefts and suspicious activity on their land.
"At this time of the year we are in the perfect rural crime storm," Federated Farmers rural security spokeswoman Katie Milne said.
"Illicit cannabis growers are at work, the rustlers are hitting farms, and we expect equipment and even fuel theft. I have no doubt in some cases the three are interrelated.
"Cannabis growers will focus on back country areas by planting among crops, which can mask plantations from all but the air," she said.
The theft of specially bred and often "irreplaceable" animals was a "double kick in the guts" for farmers.
However, farmers now had more tools to fight rural crime.
The Stop Stock Theft website, run jointly by Crimestoppers, NZX-Agri and police, allowed victims to report thefts anonymously to help build intelligence and map common crime spots.
Federated Farmers said that since July the website had received more than 1200 reports of rural crime, a number now expected to be in the "thousands".