March 27, 2009— -- The Amish are widely viewed as plain, peaceful people. Reclusive and private, most people only catch glimpses of them as they make their way through the hills of Pennsylvania's Dutch County in buggies.

But some of their perfectly manicured farms are home to a secret world. Lancaster County has been called the puppy mill capital of the U.S., and the trade is largely dominated by the Amish.

It is a world most people never see, but undercover video shot by Main Line Animal Rescue provides a startling look. Hundreds of puppies can be seen stacked in crate on top of crate. Most of those puppies will eventually be sold to pet stores, but their mothers will likely never know a home other than this.

The female breeders live their life producing litter after litter... until they can't any longer. Bill Smith, the founder of Main Line Animal Rescue, says that the dogs are then disposed of -- sometimes euthanized, sometimes shot. And it's perfectly legal.

"Unfortunately if a kennels breeds less than 60 dogs they can shoot them," he said. "If it's over 60 dogs they can't be shot."

That's why Smith spends so much time driving the country roads of Amish country, rescuing dogs from breeders. On the day "Nightline" visited, he convinced an Amish farmer to give him a female golden retriever who could no longer breed, in exchange for some free dog food. The dog -- who spent her life in a cage -- struggled to walk.

"When they come out of the rabbit hutches they walk like crabs because they don't know what it's like to walk on a proper surface," Smith said. "They drag their bodies."

There are about 300 licensed breeders in Lancaster County, and rescue workers estimate another 600 unlicensed facilities operate in barns and sheds. Those breeders go to great measures to avoid discovery. Smith says some even "de-bark" their dogs.

"The farmers, the Amish and the Mennonites, they pull the heads back and then they hammer sharp instruments down their throats to scar their vocal cords so they can't bark," he said. "So that way they can have 500-600 dogs in a barn and no one knows. As we said, it's an industry of secrecy."

Secretive and profitable. Breeders can make upwards of half million dollars a year. The Amish breeders sell the dogs at auctions and the puppies at pet stores.

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