The popular but characteristically unhealthy English bulldog may have been bred into a corner, now lacking the diversity in its gene pool to make much-needed health improvements, reports a team of University of California, Davis, researchers.

In the first broad-based assessment of the breed’s genetic diversity using DNA rather than pedigrees, the researchers confirmed earlier assumptions and provided a new glimpse of how many large regions of the genome had been altered over more than five centuries of breeding that focused primarily on changing the dog’s appearance.

“We were taken back by how little ‘wiggle room’ still exists in the breed for making additional genetic changes,” said lead author and distinguished professor Niels Pedersen of the UC Davis School of Veterinary Medicine’s Center for Companion Animal Health.

He noted that although English bulldog breeders are managing the breed’s limited genetic diversity in the best possible manner, many individual dogs today are the products of extreme inbreeding.

“We definitely would question whether further attempts to physically diversify the English bulldog, for example, by rapidly introducing new, rare coat colors; making the body smaller and more compact; or adding further wrinkles in the coat; are going to improve the already tenuous genetic diversity of the breed,” Pedersen said.

Findings from the new study are published today (July 28) in the journal Canine Genetics and Epidemiology.

From bull-baiter to national icon

The English bulldog was known to have originated in the early 1600s from a small genetic base. Its ancestors are thought to have been mastiff-type dogs, bred in Asia for strength and aggressiveness.

The breed underwent several artificial genetic bottlenecks — severe reductions in gene pool size — over the centuries, as breeders manipulated the dog’s appearance from that of a strong, ferocious “bull baiter” in bull rings of England to the iconic household pet of today. The breed was first recognized by the American Kennel Club in 1886.

Health problems common to the breed

The health problems of the English bulldog have been well documented and extend from conception through adulthood. The breed ranks second in congenital diseases and related deaths among puppies, due mainly to a number of conformational birth defects such as flat chests, splayed legs and cleft palates.

Brachycephalic, or short-headed, syndrome, which produces upper respiratory problems, is a leading cause of health problems and deaths among English bulldogs. The breed also is prone to chondrodysplasia, a skeletal disorder that may result in hip and elbow dysplasia as well as other joint and spinal problems.

Numerous other health problems are common to the breed, involving the dogs’ teeth, skin, heart, eyes and immune system.

These congenital health problems are reflected in the English bulldog’s lifespan, which has a median length of just 8.4 years.

DNA analysis probed breed’s gene pool

In this new study of the English bulldog’s genetic diversity, the researchers examined the DNA of 102 English bulldogs, including 87 dogs from the United States and 15 dogs from other countries.

These dogs were genetically compared with another 37 English bulldogs that had been brought to UC Davis to determine that the dog’s genetic problems were not the fault of commercial breeders or puppy mills.

Similar DNA studies have been carried out by the UC Davis Veterinary Genetics Laboratory for a number of other breeds and are available online.

Collaborators and funding

Collaborating on the study with Pedersen were Hongwei Liu and Ashley S. Pooch, both of the UC Davis School of Veterinary Medicine.

Funding for the study was provided by the Merial Veterinary Scholars Program, as well as the Center for Companion Animal Health and Veterinary Genetics Laboratory, both of the UC Davis School of Veterinary Medicine.