The Majority of Pitbull-Type Dogs Are Mixed Breed Dogs

A recent comprehensive study on the DNA of shelter dogs determined that the majority of dogs labeled as "pitbull-type" dogs are mixed breed dogs. The peer-reviewed study tested the DNA of 919 dogs and found that of the 244 dogs with DNA from pitbull-type ancestry, 98% of the pitbull-type dogs were mixed breed dogs while only 2% were purebred. Moreover, the study also found that the majority (62%) of the dogs with pitbull-type ancestry had less than a 50% DNA concentration from any of the four unique breeds commonly classified as the modern pitbull-type breeds including the American Pit Bull Terrier, American Staffordshire Terrier, Staffordshire Bull Terrier, and the American Bully. As a general rule, dogs must have more than a 50% DNA concentration of a specific breed to be labeled as a mix of their dominant breed - for example, "Boxer mix" - if not, they are by definition considered to be mixed breed dogs (without any breed identifiers). Therefore, the study determined that the majority of pitbull-type dogs are in fact mixed breed dogs (not "pitbull mixes") with less than a 50% DNA concentration from pitbull-type ancestry or with another non-pitbull type breed as the dominant breed (over 50%) in their DNA. These scientific facts about the DNA of pitbull-type dogs have significant implications for dog bite statistics, medical studies on dog bites, and for breed-specific legislation (BSL) as we discuss below.

DNA Test Results of 244 Pitbull-Type Dogs

98%	239 (98%) of the pitbull-type dogs in the study were identified to be mixed breed dogs by DNA and only 5 dogs were determined to be purebred.

62%	152 (62%) of the pitbull-type dogs in the study had less than a 50% DNA concentration from pitbull-type ancestry.

43%	The pitbull-type dogs in the study had an average DNA concentration of 43.5% from pitbull-type ancestry (38.5% average in shelter 1 and 48.4% average in shelter 2).

Source: A canine identity crisis: Genetic breed heritage testing of shelter dogs (PLOS ONE)

Impact On Dog Bite Statistics And BSL

The conclusions of this study have significant implications for dog bite-related data used in dog bite statistics, in medical studies on dog bites, and especially for breed-specific dog bans (BSL). For example, cities with dog bans typically impact pitbull-type dogs with more than a 50% DNA concentration from pitbull-type ancestry; therefore, the results of this study indicate that the majority (almost two-thirds) of pitbull-type dogs would not be impacted by BSL if challenged by the owner with DNA evidence. Furthermore, the results also confirm that the breed information in media reports for dog bite-related incidents attributed to pitbull-type dogs cannot be used as a reliable source for breed data as the majority of the dogs reported as "pitbulls" or "pitbull mixes" are more likely to be mixed breed dogs by DNA (or have a non-pitbull type breed dominant in their DNA). Unfortunately, unreliable and unscientific breed information in media reports is commonly used as a source for breed data in misleading dog bite statistics and in disputed medical studies on dog bites. Because of the unreliable breed information in media reports and based on the DNA evidence in this study and other studies, we'd fully support mandatory DNA testing for all serious dog bite-related incidents as this would finally validate that the majority of these incidents are not by pitbull-type dogs but instead, mostly by mixed breed dogs or by other breeds and mixes altogether. The complexities of accurately identifying a dog's breed are well known; however, the data shows that accurately identifying a dog's breed by DNA (for dogs that are impacted by BSL because of their appearance, for dog bite-related incidents, etc.) might be BSL's greatest weakness after all.

The genetics of behavior is so complex ... breed-typing is worse than stereotyping members of our own species. Breed labels would be better dropped altogether.
- Dr. Clive Wynne, ASU Canine Science Collaboratory

Updated: September 11, 2020