The Majority of Pitbull-Type Dogs Are Mixed Breed Dogs

In yet another blow to BSL, the most recent peer-reviewed study on the DNA of shelter dogs concluded that one of the main components of BSL, identifying a dog's breed based on appearance, is highly unreliable with accuracy ranging between a low of 10% and a high of 67%. Published last month, the largest study on the DNA of shelter dogs to-date also concluded that 98% of pitbull-type dogs are mixed breed dogs and that behavior is more important than heritage (DNA/breed) when considering dogs for adoption. Furthermore, the study found that dogs labeled as a pitbull-type breed had an average DNA concentration of 43.5% from pitbull-type ancestry which would challenge the majority of breed-based bans that target dogs with a genetic background of "50% or more" from pitbull-type breeds. Below, we highlight key conclusions and information from the latest scientific study to contradict BSL and breed-based bans.
Summary of the study:
  • Study published in 2018 that tested and analyzed the DNA of 919 dogs from 2 different shelters (in Arizona and California). The DNA results were then compared to the visual identification of the dog's breed by shelter staff.
  • Data includes statistics for breed identification errors between visual breed identification and DNA signatures.
  • The study was conducted by researchers at Arizona State University.
  • Study link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6107223/
Key conclusions and findings from the study:
  • 98% of the pitbull-type dogs in the study were identified to be mixed breed dogs by DNA testing. Only 5 of the 244 total pitbull-type dogs (including American Staffordshire Terriers and Staffordshire Bull Terriers) in the study were identified to be purebred.
  • Dogs labeled as a pitbull-type breed 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) and the majority (62% or 152 of 244) of pitbull-type dogs in the study had less than a 50% DNA concentration from pitbull-type ancestry.
  • Using appearance to determine breed was once again determined to be highly unreliable with accuracy ranging between 10.4% and 67.7%.
  • There is no scientific basis for judging how breed signatures interact within an individual dog.
  • The behavior of an individual dog is more important than DNA or heritage for adoption efforts.
  • ​The study rejects breed-specific legislation (BSL) as it concluded: "Because there is a lack of any scientific basis for judging how breed signatures interact within an individual dog, we believe shelters should instead focus their resources on communicating the morphology and behavior of the dogs in their care to best support matchmaking and adoption efforts."​
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 12, 2018