In the first large-scale study of its kind, Penn researchers have found evidence that puppies purchased from pet stores show an increased prevalence for behavioral problems as adults.

The paper, published in the May 15 issue of the Journal of the American Veterinary Medical Association, was a collaboration between James Serpell and Deborah Duffy of the Penn School of Veterinary Medicine, and a team of researchers led by Frank McMillan, director of well-being studies at the Best Friends Animal Society in Utah, along with Elmabrok Masaoud and Ian Dohoo of the University of Prince Edward Island’s Atlantic Veterinary College.

A 2011 study co-authored by Serpell, Duffy, and McMillan showed greater psychological problems in adult dogs rescued from commercial breeding facilities (also known as puppy mills). McMillan says he wondered what a similar examination of pet store puppies would yield, given that most of the puppies in pet stores are obtained from puppy mills.

The researchers hypothesized that the turbulent early lives of dogs in commercial breeding facilities planted the seeds for future undesirable behaviors. But the extent of the abnormalities in dogs sourced from large-scale breeders was a surprise.

“The results are pretty dramatic,” McMillian says. “The problems span so many different types of behaviors, and the differences are rather extreme for some of the behaviors.”

Not only did pet store puppies fare worse in 12 of 14 behavioral variables measured, they did not score better on any measure.

“I wasn’t expecting the effects to be so across-the-board bad,” Serpell says.

Pet store puppies showed an increased risk of aggression toward their owners and other dogs, as well as a greater chance of escaping, roaming, and running away. Neutered dogs fared somewhat better, but still showed a higher risk of aggression than neutered dogs from non-commercial breeders.

Serpell says puppies that end up in pet stores often live a disrupted early life and tend to be poorly socialized; he says they are weaned and separated from their litters too early.

Furthermore, he says “bunchers” collect puppies and take them to a holding center where they are mixed up with puppies from other mills. From there, the puppies are distributed to pet stores.

Previous research suggests that another factor contributing to psychological problems found in commercially bred adult dogs may be the high stress their mothers experienced while pregnant. The mother’s stress may play a role in improper fetal brain development, McMillan and Serpell say.

For their study, the researchers utilized Penn Vet’s C-BARQ database to compare a wide array of psychological and behavioral characteristics of 413 pet store puppies with 5,657 dogs from small-scale, private breeders.

The C-BARQ, a 15-minute online survey, is currently the only behavioral assessment instrument of its kind to be extensively tested for reliability and validity on large samples of dogs of many breeds. With more than 20,000 completed responses, the database is a gold mine of information about dog behavior that is sought by researchers from all over the world.

Until the causes of the differences detected in puppies from pet stores can be specifically identified and remedied, Serpell and McMillan say they cannot recommend that puppies be obtained from pet stores.