Most Dog Breeds Are Super Inbred, Study Finds

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Most Dog Breeds Are Super Inbred, Study Finds
English bulldogs are especially prone to breathing and other health problems due to their unique body and facial shape created through breeding.
English bulldogs are especially prone to breathing and other health problems due to their unique body and facial shape created through breeding.
Photo: Jacob King/PA Wire (AP)

New research seems to confirm the idea that many of our cutest purebred pups are also burdened by their genetics. The study determined that most dog breeds have high levels of inbreeding. What’s more, this inbreeding can contribute to various health problems and expensive vet bills over time, particularly for larger dogs.

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It’s certainly no surprise that some dog breeds aren’t blessed with robust health—often the result of long-running breeding programs that use closely related relatives to select for the traits most liked in a breed. Brachycephalic dogs like the pug or bulldog are well known for their increasingly smushed-in faces, for instance, a feature that predisposes them to breathing problems (not to mention their other issues). This new study, a collaboration between veterinary researchers in California and Finland, decided to take a broader look, hoping to get a sense of how much of an impact inbreeding is having on the purebred dog population in general.

To do this, they turned to a genetic database made up of results from commercial DNA tests of nearly 50,000 dogs, encompassing 227 breeds in total. Then they analyzed the average genetic similarity of dogs within a breed in order to estimate their level of inbreeding on a percentage scale from 1 to 100. To further check their math, they compared their results to data from past studies that studied smaller groups of breeds.

Overall, they estimated that the average level of inbreeding within these breeds was around 25%, or about the amount of genetic similarity you would see between two siblings. But while it’s fine for two members of a family to be that close, it doesn’t bode well for a population of animals that rely on genetic diversity, as most do. At levels far lower than that for humans (around 3% to 6%, the authors say), you can start to see a higher risk of hereditary disorders or other conditions influenced by genes, like cancer.