Behavioral Issues in Dogs Obtained As Puppies From Pet Stores
World Small Animal Veterinary Association Congress Proceedings, 2018
Franklin D. McMillan, DVM, DACAW
Best Friends Animal Society, Animal Care, Kanab. UT, USA

Large-scale, high-volume breeding of dogs for purposes of selling puppies occurs around the world. Because these commercial breeding establishments (CBEs) are seeking to maximize profit, the care of the dogs kept for breeding is often substandard, and in many cases inhumane. This creates the potential for innumerable problems, both physical and psychological-behavioral, to occur in the puppies.

In the United States, most puppies sold by pet stores are purchased from intermediaries, who acquire their puppies from CBEs and then distribute them to the retail stores. In addition, many puppies produced in CBEs are sold directly to the consumer over the Internet.

Conditions in the CBEs are reported to vary widely, ranging from relatively clean to squalid, noxious, and gravely detrimental to animal health and welfare. CBEs are typically characterized by large numbers of dogs, maximal efficiency of space by housing dogs in or near the minimum space permitted by law, breeding dogs spending their entire reproductive lives in their cages or runs, group and solitary housing, dogs rarely if ever permitted out of their primary enclosures for exercise or play, no toys or enrichment, minimal-to-no positive interaction with humans, and substandard or no health care. Many, but not all, CBEs have cage flooring made of wire mesh, accumulation of feces, ammonia odor, no windows and poor ventilation, inadequate protection from inclement weather and temperature extremes, insufficient or contaminated water and spoiled food, serious untreated medical conditions (e.g., advanced dental disease), extensive matting of hair, odd or stereotypical behaviors by the dogs, evidence of starvation, and presence of deceased adult dogs and puppies.

Results From Studies

Seven empirical studies have reported specific information about the behavior of dogs obtained as puppies from pet stores and/or were born in CBEs. In addition, one anecdotally reported study is included in this review of current knowledge. The studies come from 4 countries on 3 continents.

In a retrospective survey of 737 mature dogs, Jagoe (1994) investigated the relationship between early life experience and owner-reported behavior problems in adulthood. Twenty dogs were acquired from pet stores. Jagoe found that when compared with dogs from other sources, dogs obtained from pet shops showed higher levels of ‘dominance-type’ aggression (aggression directed toward people, especially the dog’s owner and owner’s family members). Pet store-acquired dogs also more often demonstrated social fears (fear of strangers, children, and unfamiliar dogs) compared with dogs from other sources.

Bennett and Rohlf (2007) studied the frequency of potential problem behaviors reported by owners in 413 companion dogs, 47 of which were obtained from pet stores. Mean scores on the unfriendly/aggressive subscale of behaviors were significantly higher for dogs obtained from pet stores and animal shelters compared with dogs obtained from breeders. Dogs obtained from pet stores also had significantly higher mean scores on the ‘nervous’ behavioral subscale than dogs who were home-bred. Pierantoni et al. (2011) compared owner-reported behaviors of 70 adult dogs separated from their mother and littermates at 30 to 40 days of age and the behaviors of 70 adult dogs separated at two months of age. 71 dogs came from pet stores. Results showed that the frequency of certain behaviors (fearfulness on walks, aversion to strangers, destructiveness, excessive barking, attention-seeking behaviors, toy possessiveness, and play biting) among dogs separated from their mother and littermates at the earlier age was higher if they came from pet shops rather than from other sources. For example, 80% of dogs separated early from litters and obtained from pet stores exhibited destructiveness more frequently compared to 20% of dogs not separated early.

McMillan et al. (2013) compared the owner-reported behavioral characteristics in 413 dogs obtained as puppies from pet stores and 5,657 dogs obtained as puppies from noncommercial breeders. They found that dogs acquired from pet stores were in general more excitable, energetic, and attached/attention seeking, and less trainable than dogs from breeders. Sexually intact pet store dogs were three times as likely to be reported showing owner-directed aggression as were sexually intact dogs acquired from breeders, and pet store dogs were nearly twice as likely to be reported to have shown aggression toward unfamiliar dogs (dog-directed aggression). Other behaviors reported more frequently in dogs from pet stores compared with breeders included stranger-directed aggression, dog-directed aggression, dog-directed fear, nonsocial fear, separation-related behaviors, escape behavior, sensitivity (disapproval), sexual mounting of people and objects, and housesoiling (urination and defecation).

Casey et al. (2014) examined the demographic variables and risk factors associated with owner-reported aggressive behavior in dogs. Results showed a 1.8 times increased risk of aggression toward family members in dogs from ‘other’ sources (the category which contained pet shops) as compared to those obtained directly from breeders.

Pirrone et al. (2016) conducted a study to compare owner-assessed potential problem behaviors in two groups of dogs: those obtained from pet shops and those obtained from official Italian breeders recognized by the Italian Kennel Club (E.N.C.I). 349 were acquired as puppies from breeders and 173 from pet shops. Compared with dogs acquired from breeders, dogs from pet stores were more likely than dogs from breeders to have an increased risk for owner-directed aggression, separation-related behaviors, and housesoiling. The authors also found a number of owner-related factors to be important, including no prior experience with dogs, nonattendance at training courses, and lack of awareness of the existence of veterinary behaviorists.

Gray et al. (2016) looked at differences in the behaviors of adult dogs based on the assumed quality of the breeding operation, using specific criteria to classify breeders into 2 groups: “responsible” or “less responsible.” The study focused on three popular breeds – Chihuahua, pug and Jack Russell terrier.

Chihuahuas acquired from less responsible breeders were reported to show more aggression toward familiar dogs, unfamiliar dogs, unfamiliar humans, and the dogs’ owners; they also showed more fear of unfamiliar humans, sensitivity to touch, separation-related behaviors, and chasing. Pugs from less responsible breeders were reported to show more fear of dogs, other fear, aggression toward familiar dogs, separation- related behaviors, and excitability. Jack Russell terriers from less responsible breeders were reported to show a decrease in trainability. Finally, an anecdotal report presented in a book chapter described a sample of 1,864 dogs exhibiting various behavioral problems, found that 220 (approximately 12%) of the dogs displayed separation-related problems (Mugford 1995). An analysis based on the source of the dog revealed that only 10% of purebred dogs obtained directly from breeders presented with separation-related problems, whereas “55% of purebred dogs originating from so-called ‘puppy farms’ or ‘puppy mills’” presented with such problems. It was not reported how it was determined that the dogs came from puppy farms or puppy mills.


The data on dogs obtained as puppies from pet stores and/or born in CBEs show that these dogs exhibit an increased incidence of behavioral and emotional problems that cause distress in adulthood compared with dogs from other sources, especially 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.

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.


1.  Bennett PC, Rohlf VI. 2007. Owner-companion dog interactions: relationships between demographic variables, potentially problematic behaviours, training engagement and shared activities. Appl Anim Behav Sci. 2007;102:65–84.

2.  Casey RA, et al. Human-directed aggression in domestic dogs (Canis familiaris): occurrence in different contexts and risk factors. Appl Anim Behav Sci. 2014;152:52–63.

3.  Gray R, et al. Puppies from “puppy farms” show more temperament and behavioural problems than if acquired from other sources. In: Proceedings of the UFAW Animal Welfare Conference, York, UK, June 23, 2016. (poster)

4.  Jagoe JA. Behaviour problems in the domestic dog: a retrospective and prospective study to identify factors influencing their development. Unpublished Ph.D. thesis, University of Cambridge. 1994.

5.  McMillan FD, et al. Differences in behavioral characteristics between dogs obtained as puppies from pet stores and those obtained from noncommercial breeders. J Am Vet Med Assoc. 2013;242:1359–1363.

6.  Pierantoni L, et al. Prevalence of owner-reported behaviours in dogs separated from the litter at two different ages. Vet Rec. 2011;169:468–473.

7.  Pirrone F, et al. 2016. Owner-reported aggressive behavior towards familiar people may be a more prominent occurrence in pet shop-traded dogs. J Vet Behav Clin Appl Res. 2016;11:13–17.


Speaker Information
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Franklin D. McMillan, DVM, DACAW
Best Friends Animal Society
Animal Care
Kanab, UT, USA

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