It’s difficult to pinpoint an exact number of puppies euthanized specifically due to puppy mills, as these operations are often not closely monitored.  Estimates related to pet overpopulation and the impact of puppy mills provide a rough idea.

• Over 3 million dogs are euthanized each year in U.S. shelters due to overpopulation. While not all of these dogs come from puppy mills, many are bred irresponsibly, either in mills or by breeders who overproduce to meet demand.
• Puppy mills contribute significantly to overpopulation by producing large numbers of puppies without concern for their health or the ability of the market to care for them. When demand drops or puppies have health issues, many end up in shelters or are euthanized.

In short, puppy mills indirectly contribute to the euthanasia crisis by overbreeding and creating an oversupply of dogs, many of which end up in shelters and face the risk of euthanasia.