August 3, 2016 – English bulldogs have been so over-bred for physical characteristics, there is not enough diversity in their gene pool to make much-needed health improvements, a new study has found.
It is the first broad-based assessment of the breed’s genetic diversity using DNA rather than pedigrees. The researchers confirmed earlier assumptions and provided a 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 D Niels Pedersen of University of California Davis School of Veterinary Medicine’s Center for Companion Animal Health, adding 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.
“The English bulldog will not die out as a breed because of its long history, popularity, and historical ties. However, it is highly unlikely that the breed can survive in its present state of ill-health. If something is not done soon, the health problems that are already severe will only continue to get worse,” Dr Pedersen told Pet News Today.
Dr Pedersen said he believed that the increasing health issues will ” …ultimately cause the breed to lose popularity”.
“As demand for puppies declines there will be fewer and fewer breeders and those who are left, who will be the true lovers of the breed, will have to pick up the pieces. That will probably require extensive use of out-crossing and back-crossing,” he added.
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 recognised 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 the study, 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.
“Breeders often say that the unhealthy dogs are produced by backyard breeders (not professional show breeders) or puppy mills (breeding entirely for profit). If unhealthy dogs seen at our teaching hospital were products of puppy mills and backyard breeders and are genetically inferior as believed by professional breeders, they should be genetically different from professionally bred dogs. The study showed them to be genetically identical, thus making this belief untrue. In other words, professional breeders cannot blame backyard and commercial breeders for the health problems of their breed,” Dr Pedersen said.
Pet News Today asked Dr Pedersen if he thought the research might impact the promotion of specified breed standards in dogs.
Vets urge revision of breed standards to protect animal welfare
British Veterinary Association (BVA) President Sean Wensley said the research reflected the serious health problems BVA members were seeing in their daily work as vets.
“Revision of breed standards, to include evidence-based limits on physical features such as muzzle shortness, and full consideration of other approaches such as out-crossing, is now needed to ensure high risk breeds, such as the English bulldog, do not continue to suffer unnecessarily.
“Vets are reporting concerning trends in dog health and welfare linked to the rise in ownership of brachycephalic breeds, such as bulldogs, and we are unequivocal in the need for all those with roles to play – including vets, breeders, breed societies, the pet-buying public as well as others – to take action.”
The health issues brachycephalic breeds suffer caused by inbreeding include severe lifelong breathing difficulties, corneal ulcers, skin disease, a screw-shaped tail which is linked to painful spine abnormalities, and the inability to give birth naturally.
“As part of their pre-purchase research, prospective dog owners should consider the health harms perpetuated in dogs by purchasing brachycephalic breeds and choose a healthier alternative breed, or crossbreed, instead, and local veterinary practices are ideally placed to give this advice. Brachycephalic dogs should not be seen as cute or desirable, rather as dogs predisposed to a lifetime of poor health, and English bulldogs should not be hailed as a national symbol for the UK where animal welfare is strongly valued.
“Vets have a duty to always prioritise the best interests of their pet patients, which, for affected animals, can involve performing surgical procedures to correct conformational disorders. They have a concurrent duty to be part of initiatives that aim to address the health and welfare of a breed beyond the individual affected animal. This is why BVA promotes the importance of vets submitting data on caesarean sections and conformation-altering surgery to the Kennel Club, to improve the future of dog health and welfare. We recognise and take seriously vets’ responsibility to develop and contribute to all such initiatives that aim to address the health and welfare of these animals and we will continue to work with all stakeholders who can positively influence and improve the health and welfare of brachycephalic breeds,” Sean added.
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.