What percent of dogs come from puppy mills in the US?

Dog fighting is an illegal, vicious underground organized crime that, although completely outlawed, has reached epidemic proportions in the United States. In all fifty states, the dog fighting laws exist independently of the general anti-cruelty statutes and most are felonies carrying much stiffer penalties than the general anti-cruelty laws.

A federal bill, S. 382, created the Animal Fighting Prohibition Enforcement Act of 2005. The Act amends the United States Code, making it a crime for any person to knowingly sponsor or exhibit an animal in an animal fighting venture if any animal in the venture was moved in interstate or foreign commerce. Additionally, it is unlawful for any person to knowingly sell, buy, transport, or deliver, or receive for purposes of transportation, in interstate or foreign commerce, any dog or other animal for purposes of having the dog or other animal participate in an animal fighting venture.