A new study by University of California, Davis researchers shows that English bulldogs, a breed prone to a number of congenital health problems, have been so overbred that their genetic pool may now be too small to make much-needed health improvements.
The objective of the study, according to the researchers, was to assess whether the breed retains enough genetic diversity to correct the genotypic and phenotypic abnormalities associated with poor health, to allow for the elimination of deleterious recessive mutations, or to make further phenotypic changes in body structure or coat.
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 U.C. Davis to determine that the dog’s genetic problems were not the fault of commercial breeders or puppy mills.
“We were taken back by how little ‘wiggle room’ still exists in the breed for making additional genetic changes,” said lead author Niels Pedersen, DVM, Ph.D., of the U.C. 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,” Dr. Pedersen said.
The breed, which dates back to the early 1600s, is thought to have ancestors from mastiff-type dogs, bred in Asia for strength and aggressiveness. Five centuries of breeding changed the former “bull-baiter” into its now popular breed.
The study reveals that the breed has lost considerable genetic diversity through such things as small founder population and artificial genetic bottlenecks resulting from highly focused selection for specific desired physical traits.
This loss of genetic diversity and extreme changes in various regions of the genome will make it very difficult to improve breed health from within the existing gene pool, the researchers concluded.
The study was published July 28 in the journal Canine Genetics and Epidemiology.