Insight through Science and Nature: Diminishing Genetic Variety in Dog Breeds

While researching for canine parvovirus vaccination campaign, I stumbled upon an unexpected fact from the Journal of the American Veterinary Medical Association: Rottweilers, American Pit Bull Terriers, Doberman Pinschers, and German Shepherds were all significantly more likely to be affected by CPV than mixed breed dogs. At first glance, this statement was puzzling - CPV is a viral illness, and therefore it shouldn’t be linked to genetic factors such as the dog’s breed. However, further research unveiled the intricate relationship between centuries of artificial selection in dogs and nuanced aspects of their health today, with substantial scientific evidence providing a case for a paradigm shift in how we approach pedigree breeding.

For millennia, humans have been intentionally and unintentionally altering the genome of surrounding species, in an attempt to mould natural resources for our own survival. While the genetic manipulation of our environment through selective breeding has undoubtedly allowed for human populations to flourish across the globe, in the present, it can undermine some of the fundamental aspects of an organism, such as its immunity.

Selective breeding refers to when humans choose to breed parents with certain traits in order to produce offspring of a particular species that has more desirable traits, such as improved crop yield or higher quality animal products. This intervenes with the much slower, almost accidental process of natural selection, in which varying environmental factors shape the genome of a species, leading to genetically diverse and resilient populations. Perhaps no animal is a better example of selective breeding than the dog, which has been transformed from the undomesticated wolf into a species colloquially known as “man’s best friend.” What makes the dog’s story in particular, so remarkable is the sprawling variety of breeds present within the species, a clear illustration of the extent of selective breeding’s influence.

Historically, selective breeding of different dog breeds would have been primarily due to need, as growing human societies found responsibilities for the species uniquely apt to life with humans. Different breeds of dogs were developed to serve purposes in guarding, hunting and, at the advent of agriculture, herding. However, in the last 150 years, a dramatic shift has occurred in how the selective breeding of dogs is approached, and it is one with severe consequences that are still being charted. Since Victorian times, humans have sought to reach the ideal appearance for various breeds, heightening specific physical features as dogs began to take on a role of companionship instead of labour. Rather than being rooted in the needs of civilization, dog breeding is now based on conformational traits, or the aesthetic aspects of the dog.

While the “Victorian Explosion” in dog breeding made way for the formation of the over 400 distinct dogs breeds we now know and love, many of these breeds are now genetically predisposed to detrimental health conditions. Generations of inbreeding to produce purebred dogs increased the chances of an individual receiving both copies of recessive traits, which therefore enables their expression. This is known as homozygosity, and as many genetic diseases are caused by recessive genes, has led to a dramatically increased prevalence of autoimmune disorders in Siberian huskies, respiratory concerns in bulldogs, epilepsy in beagles, back problems in dachshunds, and numerous other breed-specific proclivities toward adverse health conditions. One of the most pervasive and perhaps unexpected repercussions of dog breeding the way it has so devastatingly affected the immune system.

The inherent immunity of an animal is something that seems almost sacred. Although we enhance it through vaccines and supplements, an animal’s immune system is largely a product of its age, sex, environment, and genetics, elements that seem distinct from human actions. Yet, as humans honed in on appealing features by breeding genetically similar dogs, genetic variety within dog breeds rapidly deteriorated. As a result, there is less variety in haplotypes, or genes related to the immune system within a breed, thereby weakening immunity on the individual level. There are two main classes of canine haplotypes, DLA (dog leukocyte antigen) Class I and DLA Class II. A “high” number of haplotype variation within a breed is considered to be approximately 40 versions of DLA Class I and 30 versions of DLA Class II haplotypes, although this is still low compared to estimates for dogs from before the Victorian Explosion. In contrast, Doberman Pinschers, one of the breeds mentioned in risk factors for canine parvovirus, has only around 10 versions of DLA Class I and 10 of DLA Class II. This severe loss of variety within the genes involved in immunity has undoubtedly taken a toll on the immune system in purebred dogs today, and in the words of Dr. Carol Beuchat from the Institute of Canine Biology, “we could eliminate every mutation in a breed but this would not produce "healthy" dogs if the immune system has been compromised.” The issue regarding canine immunity is therefore not one of faulty mutations or hereditary disease but due to a widespread lack of genetic diversity.

Despite this concern regarding dog health, here in India breeds such as Labradors and German Shepherds are only increasing in popularity, due to the perceived status that comes with a pedigree animal in comparison to an indigenous stray. Yet these dogs, who have been cross bred on the streets without human intervention, are in possession of more varied haplotypes, and therefore less susceptible to serious illness. Although there is tendency to focus on breed notoriety when picking out a furry friend, long-term health and genetic predispositions of the animal are an essential component of its welfare.

The case study of diminishing haplotypes within dog breeds is a fascinating demonstration of how our mutualistic relationship with other species is often enhanced when guided by science. 150 years ago, when DNA had only just been isolated by Frederick Miescher, there was no way to predict the consequences that generations of dog breeding to come would have on haplotype variation within breeds, yet in retrospect, the connection is stunningly clear. Now, as we craft solutions to the consequences faced by the canine immune system, answers may not seem singular or easily apparent. On the contrary, the complexities of this issue provide an opportunity for the re-evaluation of human interactions with animals, specifically in terms of genetic alteration. Key to achieving animal welfare is enriching the experiences and quality of life for animals - how better to accomplish this aim than through the variety that nature offers?