A review of 7 published studies and 1 anecdotal report involving dogs born in high-volume commercial breeding establishments and sold to the consumer directly via the Internet or indirectly through retail pet stores revealed an increased incidence of behavioral and emotional problems that cause distress in adulthood compared with dogs from other sources, especially noncommercial breeders. The most consistent finding among studies is an increase in aggression, which is most commonly directed toward the dog's owners and family members but also to unfamiliar people, and other dogs. Increased fear was also identified in response to unfamiliar people, children, other dogs, nonsocial stimuli, and when taken on walks. Undesirable behaviors related to separation and/or attention seeking and a heightened sensitivity to touch have been reported. Because of how dogs sold through pet stores and/or born in commercial breeding establishments are bred, housed, weaned, transported, handled, homed, and raised, potential contributing factors for these reported outcomes are numerous. Some key factors include genetics, early-life stimulus deprivation (inadequate stimulus exposure, inappropriate or lack of social exposure), stress (prenatal maternal stress and postnatal early-life adversity), early weaning and maternal separation, transport and pet-store-related factors, and owner-related factors such as inadequate knowledge and experience with dogs as well as different levels of commitment to the pet dog. All published studies suggest a role for major stressors during puppy development from the prenatal stage through adolescence in the development of many behavioral problems. Accordingly, for any dog breeding operation, a standard of care that adequately redresses the welfare of the mother and pups and the risk of later behavior problems attendant with early stress and distress need to be formulated and followed in a manner supported by the emerging data.
McMillan, F. D. (2017, May 1). Behavioral and psychological outcomes for dogs sold as puppies through pet stores and/or born in commercial breeding establishments: Current knowledge and putative causes. Journal of Veterinary Behavior: Clinical Applications and Research. Elsevier USA. https://doi.org/10.1016/j.jveb.2017.01.001