Today, bulldogs are known for their flat, wrinkly faces and stout bodies. They aren't the sturdiest dogs, and require human assistance to reproduce. Less than two hundred years ago, however, bulldogs had an athletic physique with an elongated muzzle and relatively wrinkle-free face. But after a century and a half of selective breeding, bulldogs have lost their sturdy frame.
For thousands of years, people have been breeding animals to produce the fastest horses or the best hunting dogs. But, according to a Scientific American article, over the past 200 years, dog breeders began mating related animals hoping to produce dogs with show-winning features. Because of this, genetic and health issues proliferate in certain modern dog breeds.
Brachycephalic, meaning "short-headed" dog breeds are prime examples. These breeds—which include pugs, bulldogs, Pekingese, and Boston terriers—have short, flat throats and airways as a result of selective breeding practices.
Selective Breeding and Genetic Diversity
In any population of organisms, genetic diversity is key for survival. This is because greater genetic variation increases a population's odds of adapting to the pressures of a changing environment. In a genetically diverse group, it's more likely that there are some individuals who have genes that will help them survive in the changing environment. As a result, those who are better adapted to the environment can then pass on their genes to later generations.
With low genetic diversity, one environmental change could affect the entire population. For example, if a group of organisms have largely the same genes for immune regulation, one nefarious disease could affect the whole population. In fact, this might be the case with bulldogs, as generations of inbreeding have reduced the breed's variability. A 2016 study in Canine Genetics and Epidemiology found that in the bulldog genome, the region regulating the immune system was largely the same for the 139 bulldogs in the study.
Generations of inbreeding and selecting for a new physique may have permanently altered the bulldog breed. Image source:WikimediaCC BY-SA 4.0
When humans step in to breed dogs, they can unknowingly affect traits that have helped the breed thrive for generations. For example, one recent study that looked at the genes of about 100,000 dogs found that purebred dogs were more likely to be affected by genetic disorders. Additionally, breeding for a specific appearance can cause other health problems to spread throughout a breed. In the case of bulldogs, this includes skin disease, spinal issues, breathing problems, and the inability to give birth naturally.
What Can be Done?
Part of the problem stems from a lack of communication between consumers, veterinarians, and breeders. Consumers unaware of how selective breeding affects a dog's health may inadvertently fuel demand for the breed, encouraging harmful breeding practices. For example, demand for the cute, flat face of bulldogs, the fifth most popular breed in the U.S., and pugs has led the breeds to develop shorter skulls, leading to breathing troubles and overheating.
Boston terriers, another brachycephalic breed, suffer from similar breathing issues as bulldogs and pugs. Image by Svenska Mässan, CC BY 2.0
In a statement from the British Veterinary Association, President Sean Wensley urged for revisions to breeding standards, and "As part of their pre-purchase research, prospective dog owners should consider the health harms perpetuated in dogs…and local veterinary practices are ideally placed to give this advice." Veterinary Ireland has also taken action, calling for bans on advertising using flat-faced dogs and cats.
Breeders can work responsibly by avoiding inbreeding and applying genetic science. According to the Humane Society, responsible breeders try to prevent health issues in a parent from passing on to offspring. National kennel clubs that set standards for breeds have also revised some of their qualifications to promote healthier breeding practices.
Policymakers can play a role, too. In 2018, the evidence that selective breeding imparts serious health issues prompted the United Kingdom to pass legislation stating that licensed dog breeders cannot keep a dog for breeding if it would detrimentally affect the animal's health and welfare or that of its offspring. Whether this has led to any improvement in breeding practices is not clear.
But, even responsible breeding might not be enough to reinvigorate some breeds, like bulldogs. Because the gene pool is so small, crossbreeding may be the only way to improve bulldog health.