PORTLAND, Tenn. -- The Sumner County Sheriff's Department is investigating a border collie rescue operation in Portland, after finding about 100 of the animals living in filth.

Images: Border Collies Seized From Sumner Co. Kennel | Watch This Story

According to Sheriff Bob Barker, investigators seized the animals after complaints surfaced about the conditions of the operation on North Center Point Road. Investigators have visited the operation before on similar allegations but have never filed charges against the owner and operator.

Scotlund Haisley of the National Humane Society said they recovered dogs that were living in a bathtub.

"These dogs are just living in muck," Haisley said. "I don't even want to call it mud. It's muck. It's a combination of mud, feces and urine. And you can smell me; imagine what the property smells like."

According to the sheriff, the kennel's owner, Richard Swafford, who also breeds the dogs, is reluctantly cooperating with investigators and reported he's had difficulties keeping up with the operation and maintaining a consistent staff of employees. He called Friday's raid a blessing.

Swafford said he was selling the puppies but that the money made off of those sales was spent on dog food and other medical care for those adult dogs that are often difficult to adopt out.

The Sheriff's Department spent much of Friday processing the kennel and the dogs. The U.S. Humane Society will help relocate the animals and may set up a temporary shelter in Sumner County or send the animals to out-of-state shelters.

Humane Society officials called the operation a puppy mill, while the owner said he was just trying to save animals that would have otherwise been euthanized.

"No dog here has it good. I mean, all the conditions are rough," said Haisley.

The Sheriff's Department hasn't filed charges against Swafford, but it's a possibility as the investigation continues, according to the sheriff.

Reporters Josh DeVine and Jennifer Johnson contributed to this story.