The endearing physical quirks that make English bulldogs so lovable might also be killing them.
A new study of genetic diversity in the breed has revealed that the existing bulldog genetic stock is not diverse enough to allow breeders to improve the breed's health via genetic manipulation from within the gene pool.
"The English bulldog has reached the point where popularity can no longer excuse the health problems that the average bulldog endures in its often brief lifetime. More people seem to be enamoured with its appearance than concerned about its health," says Niels Pederson of the University of California's Center for Companion Animal Health.
In this study, researchers examined a sample of 102 English bulldogs; 87 of the dogs were from the U.S., while the remaining 15 came from other countries. The researchers ran a genetic comparison of these 102 dogs with 37 more English bulldogs treated at UC Davis for a variety of health problems. This comparison was designed to help researchers determine whether or not commercial breeders or puppy mills were to blame for the dogs' genetic issues.
Pedersen, lead author of the study, explains; "We found that little genetic 'wiggle room' exists in the breed to make additional genetic changes."
And although the majority of the changes humans have made to the breed have occurred over a period several centuries, they have accelerated drastically in recent decades.
"Breeders are managing the little diversity that still exists in the best possible manner, but there are still many individuals sired from highly inbred parents," Pederson adds.
The genetic roots of the English bulldog trace back to a founding population of only 68 individuals after 1835. Since then, humans have continually manipulated the breed. They have reduced its population size in order to achieve desired changes in the bulldog's phenotype. These manipulations have only diminished the breed's genetic diversity.
Furthermore, many of the changes have affected the genes that dictate and regulate immune responses. Consequently, the English bulldog, one of the world's most popular dog breeds, is also one of the unhealthiest.
In an effort to expand the English bulldog's genome and improve the breed's health, some Swiss breeders now cross the breed with the Olde English Buldogge. The result is the Continental bulldog. The Continental bulldog represents an important first step in improving the English bulldog's genetic diversity. However, many breeders feel that the Continental bulldog - and any future deviations from the original breed standard - do not represent a true English bulldog.
This study is the first DNA-based assessment of genetic diversity in the breed. Prior studies of the English bulldog relied on pedigrees rather than DNA analysis. The research will be published in the journal Canine Genetics and Epidemiology and you can read more about it here.