However, a police spokesman said there was no evidence the reels had been taken by activists.
Southern District Police urged farmers using electric-fence reels for winter grazing to remain vigilant following the theft of several single and triple reels from paddocks near the road in Drummond, Dipton and Ryal Bush in the past three weeks.
"We recommend reels are placed as far away from the roadside as possible, and keeping them out of the sight of potential thieves," police warned in a social media post.
Federated Farmers Southland president Jason Herrick, a sharemilker in Northern Southland, said he believed there was a link between a prevalence of animal-rights activists in the region and the missing reels.
Drones featuring cameras were being flown across farms in Southland, which he believed were being operated by activists searching for poor winter-grazing practices.
The removal of a temporary fence from a winter crop could result in the death of cattle because it gave them open access to feed, which the fence had been controlling.
Overindulging in certain winter crops could be "very dangerous" and cause a raft of animal welfare issues.
For example, if cows were offered too much fodder beet too quickly, it could result in rumen acidosis, which could be deadly.
"All the activists care about is their own personal beliefs and they don’t know the ins-and outs of farming."
If the reels were stolen, any farmers "strapped for cash in tough economic times" were urged to reach out for help by contacting the Rural Support Trust or Federated Farmers.
He doubted the reels were taken by a farmer because they would be aware of the animal-health issues the removal could cause cattle.
A drone flown across a farm at night in Southland recently featured a spotlight, he said.
Farmers’ levels of "anxiety and anger were through the roof".
He urged farmers to refrain from shooting down the drones to stay on the right side of the law.
"Don’t do something you’ll regret later on."
Rather than confronting an activist, farmers should get evidence of a person acting suspiciously or illegally, such as flying a drone across private property, and give it to police.
Mr Herrick was unaware if any activists in Southland were associated with any animal rights group.
Safe chief executive Debra Ashton said she would be extremely surprised and disappointed if activists had taken the reels.
"It is not our approach."
She did not support the use of direct and illegal action on farmers.
Mr Herrick should obtain evidence before making an accusation, she said.
She was not aware of anyone flying drones across farms in Southland.
Anyone with information which might assist police inquiries into the stolen reels could call 105, or make an online report at 105.police.govt.nz, using reference file number 240704/8171, he said.
