For those who have never heard of a puppy mill, it's equivalent to solitary confinement  for young dogs, with substandard conditions.
As a result, some of the dogs that emerge from puppy mills look either malnourished or in overall bad health.
Channel 4 Action News went undercover to investigate dogs pulled from puppy mills.
Fed and bred. That's it. No walks. No interaction with humans. That means the dogs eat and relieve themselves in the same 2-by-2-foot cage for about eight years until their breeding days are done.
And it gets even worse. Channel 4 Action News went undercover to an Amish dog auction in Holmes County, Ohio.
Auctions like the one Channel 4 Action News attended are illegal in Pennsylvania, so people travel two hours west, where it's legal. There, old puppy mill dogs are put out to pasture or their pups are auctioned off so they can start a new breeding cycle.
A dog so frightened it could barely stand on its own was auctioned off in a room with more than 300 people. Up until then, the only human the dogs have known is the hand that  fed them -- nothing more.
Deborah Ethier is a self-proclaimed animal rescuer. She rescued nine dogs by buying them at the auction for $2,100. But it was too late for a 2-year-old Boston  terrier who already had three litters. She is losing her uterus.
"The muscle area becomes so weakened, it does what they call a prolapse and it just literally falls out," Ethier said.
"Is that because of overbreeding?" Ingram asked.
"Overbreeding," Ethier said.
"How many times has she been bred?" Ingram asked.
"How old is this dog, 2?  She's probably been bred at least three times," Ethier said.
Another animal breeder said that's common. "Just from being weak, overbred," said the breeder, who asked not to be identified.
"When you say overbred, how many times?" Ingram asked.
"Every six months," the breeder said.
"Every six months?" Ingram asked.
"Every six months. Never a break," the breeder said.
"From the first two or three years of life?" Ingram asked.
"From the time they're eight to 10 months old -- when their first heat starts -- every six months," the breeder said.
"There was one puppy in the auction when they said all of her pups died.  Is that common?" Ingram asked.
"Yes.  It's very common," the breeder said. "They're fearful, and a lot of times, they will eat their babies.  It's very common."
Animal rescuers don't just fault the Amish, but also the federal government. Puppy mills are legal because the federal government considers those puppies livestock -- not pets. They're caged for their entire breeding life, then sold -- not just to far-out auctions, but to some pet stores.
"No responsible breeder would ever sell a dog to a pet store," animal rights activist Pam Maurer said. "I've seen what's been going on, and I'm just appalled, dismayed. And I spent nights laying in bed, wondering how this situation can be rectified."
U.S. Sen. Rick Santorum, R-Pa., introduced legislation to crack down on puppy mills and has fought for changes for 10 years.
"People who are breeding large quantities of dogs now but selling them directly have an exemption under the Animal Welfare Act, and that has to change," Santorum said. "Unfortunately, a lot of folks -- including the ones you've been investigating -- are exempted under the law."
Santorum and animal rescuers said an overwhelming number of puppy mill operators are Amish.
"Why the Amish? Why is it so prevalent in their community?" Ingram asked.
"I don't know. Maybe it's a different mindset in regards to animals," Santorum said.
Channel 4 Action News tried to ask some Amish breeders, but they wouldn't talk.
Many animal rescuers said dogs coming from puppy mills end up in common pet stores. So when purchasing a dog from a pet store, ask about its history.