I have read and seen many things about puppy mills. I even had the chance to go to a dog auction (which is a whole post by itself). This video is by far the sadest thing I have seen.
Please note this are graphic and sad images.
Remember, please get your dogs from a shelter, rescue, or a responsible breeder. Every dog at a pet store is from a puppy mill, no matter what they tell you.
While not all puppy mills are this aweful, most are and are not caught. For more information about puppy mills visit- http://www.nowisconsinpuppymills.com/