BRANT COUNTY, Ont. -- Police are investigating what they're calling an act of vandalism -- and what a farm spokesperson is calling an act of animal rights extremism -- after some 500 minks were set loose in southwestern Ontario overnight Friday.

Early Saturday morning, Ontario Provincial Police were called to the Brant County, Ont., farm. It had been broken into -- holes were cut into the walls, and the mink inside were set loose, investigators said.

"It seems like an organized attack by animal rights extremists who have attacked many farms in southern Ontario in the last several years," said Nancy Daigneault, vice president of the International Fur Federation. "They break into a farm at night and they open all the cages to release the minks."

Daigneault said that last year, a self-identified animal rights group made threats against the farm. She said the threats were reported to police.

But police wouldn't say whether there's anything that suggests activists were involved in this case.

The farm owner declined an interview, but said that Daigneault was his spokesperson.

The affected farm is one of about 300 fur farms in Canada, according to Statistics Canada, and mink is the most popular farmed fur.

Daigneault said most of the animals were recovered, but many of them had recently given birth. The newborns, called kits, were separated from their mothers, she said.

Provincial police Const. Ken Johnston said there's no guarantee the babies would be able to find their way back to their mothers to nurse, and Daigneault added that even if they could, there's no guarantee the babies could survive the trauma of separation.

"The farmer's saying he thinks they may lose three-quarters of the babies," Johnston said. "I think that whoever did this, that should weigh heavy on their conscience."

Police are continuing their investigation, and they're asking anyone with information to come forward.