Analysis by Dr. Karen Shaw Becker
People who love dogs also often love learning about different breeds and their specific traits such as physical appearance, temperament, behavior, and others. After all, if dog lovers weren’t curious and interested in knowing more about different breeds, there’d be no market for doggy DNA tests such as the Wisdom Health (which has the largest dog DNA database in the world), Embark, and DNA My Dog.
What many people don’t realize, however, is that the genetics that convey particular attributes to various breeds are frequently the result of inbreeding. In fact, the results of a recent study published in Canine Medicine and Genetics have revealed that the majority of dog breeds are highly inbred, which has contributed to an increase in disease and lifelong veterinary care costs.1
According to lead study author Danika Bannasch, a veterinary geneticist at the University of California, Davis:
“It’s amazing how inbreeding seems to matter to health. While previous studies have shown that small dogs live longer than large dogs, no one had previously reported on morbidity, or the presence of disease. This study revealed that if dogs are of smaller size and not inbred, they are much healthier than larger dogs with high inbreeding.”2
Several years ago, Bannasch fell in love with the small size, disposition, and intelligence of the Danish-Swedish farmdog and decided to import one from Sweden.
She learned that the breed has a low level of inbreeding thanks to a relatively large founding population (200 dogs), coupled with breeding programs that focus on function rather than looks. In addition, Bannasch discovered that according to insurance health data on breeds, the farmdog is one of the healthiest.
25% of Dogs in Europe Are Inbred
The international team of researchers led by Bannasch discovered that the average inbreeding based on genetic analysis of just under 50,000 dogs across 227 breeds, primarily in Europe, was close to 25%, which is “the equivalent of sharing the same genetic material with a full sibling.”
These levels are considered to be well above the measure of safety for either humans or wild animal populations. (In humans, just 3% to 6% levels of inbreeding are linked to increased occurrence of complex diseases and other conditions.)
“Data from other species, combined with strong breed predispositions to complex diseases like cancer and autoimmune diseases, highlight the relevance of high inbreeding in dogs to their health,” says Bannasch.
In dog breeds with a high incidence of inbreeding, contributing factors are often a small founding population coupled with strong selection for a particular look rather than health or purpose.
The study also revealed a significant difference in rates of disease between brachycephalic (short skull and snout) and non-brachycephalic breeds. This finding wasn’t a surprise, but the researchers decided not to include brachy breeds in the final analysis on effects of inbreeding on health.
No Easy Solution
Bannasch isn’t sure there is a way to remedy the situation with inbred breeds. According to a UCDavis news release on the study:
“People have recognized that creating matches based solely on pedigrees is misleading. The inbreeding calculators don’t go back far enough in a dog’s genetic line, and that method doesn’t improve overall high levels of population inbreeding.”3
Preserving the genetic diversity, and thereby the health of a breed, according to Bannasch, requires careful management of breeding populations to prevent further loss of existing genetic diversity. This can happen only through breeder education and monitoring of inbreeding levels using direct genotyping technologies.
Where feasible, says Bannasch, outcrossing (breeding unrelated dogs) can increase genetic diversity, but it isn’t a guarantee that overall breed diversity will increase or that a reduction in inbreeding will be achieved. What is clear is that when it comes to the handful of breeds with low inbreeding levels, every effort should be made to maintain existing genetic diversity.
I interviewed epidemiologist and veterinarian Dr. Brenda Bonnett about this quandary when we wrote The Forever Dog book last year. She explained that geneticists, vets and breeders from around the world have come together to create the Harmonization of Genetic Testing Database via International Partnership for Dogs, in an attempt to better address narrowing gene pools and genetic deletions on a worldwide basis.
Poster Pup for Poor Breeding: The English Bulldog
There are several dog breeds that have suffered at the hands of humans determined to exaggerate certain physical features to the detriment of the dogs’ health. One of the most damaged is the English bulldog.
According to veterinary journal dvm360:
“They can’t fit through their mothers’ birth canals. They’re plagued by serious respiratory problems because they are brachycephalic. They die at a median age of a little over 8 years of age.”4
Not only do English bulldogs have brachycephalic syndrome due to their pushed in faces, they’re also prone to a long list of other health problems, including:5
- Flat chest, a chest bone deformity in which the middle of the chest appears to be flat or concave, rather than slightly rounded
- Splayed legs, a condition in which the muscles that pull the legs together are weak, causing the dog to lie flat on the floor and paddle around like a turtle
- Cleft palate, in which the roof of the mouth and/or lip fail to close during gestation
- Chondrodysplasia, a skeletal disorder that can cause hip and elbow dysplasia as well as other joint and spinal problems
- Dental, eye, skin, heart, and immune system problems
English bulldogs rank second of all breeds in congenital diseases and related deaths among puppies. The health problems of these poor dogs are well documented and are present from conception through adulthood.
Is the Damage Irreversible?
An earlier group of researchers at the University of California, Davis analyzed the DNA of 102 English bulldogs, including 87 dogs from the U.S. and 15 from other countries.6 They did a genetic comparison of those dogs with another 37 English bulldogs brought to UCDavis for various health problems.
The study was the first large-scale assessment of the genetic diversity of English bulldogs that used DNA rather than pedigrees. Study results confirmed a number of large regions of the genome have been altered as a result of centuries of breeding designed to manipulate and exaggerate the breed’s appearance.
Sadly, the researchers concluded it would be extremely difficult, if not impossible to return the breed to good health.
“We were taken back by how little ‘wiggle room’ still exists in the breed for making additional genetic changes,” said lead researcher Niels Pedersen, DVM, PhD, of the UC Davis Center for Companion Animal Health.7
‘May Have Been Bred Into a Corner’
Excerpted from the UCDavis Study’s ‘Plain English Summary’:
“The English bulldog is one of the most popular breeds in the world because of its child-like appearance and demeanor. The alterations in body type and behavior needed to create the breed have required physical changes well beyond its village dog ancestors.
These changes have occurred over hundreds of years but have become particularly rapid over the last decades. Unfortunately, popularity does not equate to health and there have been increasing pressures on breeders to moderate the extreme physical changes that now affect the breed and its health.
Improving health through genetic manipulations presumes that enough diversity still exists to improve the breed from within, and if not, to add diversity by outcrossing to other breeds.
The 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.
Loss of present genetic diversity is further threatened by rapid integration of new coat color mutations, increased wrinkling of the coat, and attempts to create a more compact body type.
Contrary to current beliefs, brachycephaly and the resulting breathing problems in the breed are the result of complex changes in head structure, and cannot be corrected by merely lengthening the face.
Furthermore, other issues in English bulldogs need to be addressed, including many serious health problems that are not associated with brachycephaly, but are intrinsic to inbreeding.”8
According to Pederson, “… 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.9
Tragically, the English bulldog, according to the UCDavis researchers, now lacks the diversity in its gene pool to make desperately needed health improvements. This means if you have your heart set on a purebred dog, there are only two ethical answers: rescue one, or partner with a preservation breeder 100% committed to intentionally creating genetic diversity. Never buy a puppy from a pet store. Ever.