In the first edition of On the Origin of Species, Charles Darwin mentions dogs 54 times. He does this mainly because the extraordinary variation between dog breeds wonderfully illustrates the power of selection. For most of the approximately 15,000 years since their domestication, dogs have been selected by humans for their usefulness as hunters, retrievers, shepherds, guardians or companions.
As modern breeds became recognizable, the extent to which a dog aligned with the shape, size, and coat expected for its breed (called “conformation”) became more important. So significant, in fact, that just a few years before On the Origin of Species hit bookstores, the world’s first conformation-based dog show was held at Newcastle-upon-Tyne Town Hall in England. .
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In 1873 the UK Kennel Club was formed to, among other things, regulate the showing and breeding of dogs. Similar organizations soon followed in other countries. Judging and breeding criteria for conformation were formalized in breed standards which are now administered by kennel clubs around the world.
Unfortunately, breeding for the standard in some breeds has resulted in serious health and welfare compromises, especially in cases where the wording of the standard encouraged the exaggeration of certain characteristics.
Breeds to Watch
The Kennel Club Breed Watch highlighted that approximately 15% of breeds have “breed-specific conformation issues that can lead to health issues” and an additional 4% of breeds in which “some dogs have conditions or visible exaggerations that may cause pain or discomfort. ”.
Fortunately, there is now global coordination to address these issues. The International Partnership for Dogs (IPFD), which works with many global breed regulatory organizations, highlights “extremes of conformation.”
Without up-to-date prevalence data on each disorder, we cannot be sure about the effectiveness of watch lists or changes in breed standards in addressing these disorders. Also, in 2009-2010, one of us (Paul McGreevy) helped show that while some of the concerning conformation issues are related to breed standards, others are inherited disorders unrelated to breed standards. race.
So even if there were no breed standards and dogs were bred solely for their health and well-being, many hereditary disorders would still arise. In fact, the vast majority of hereditary disorders have nothing to do with conformation.
All inherited disorders (and all desirable inherited traits) are, in essence, the result of random DNA mutations that have occurred and continue to occur in all species.
The number of known inherited disorders varies enormously from species to species, mainly reflecting the extent of research efforts. For example, the number of single gene disorders documented in humans is over 5,300, while the figure for dogs is less than 300. As many inherited disorders that occur in humans could also occur in dogs, the current number for dogs is probably just the tip of the iceberg.
A worldwide research effort provides an ever-increasing number of DNA tests for known canine inherited disorders, allowing (in many cases) the elimination of the disorder. National Kennel Clubs provide helpful advice on testing and public access to test results on individual dogs. The IPFD provides global information to breeders on the harmonization of genetic testing for hereditary diseases in dogs.
One of us, Paul McGreevy, was part of an international team that developed a risk assessment criterion for determining priorities for research and control of inherited disorders. A major component of this score is the prevalence of a disorder in a particular breed.
Estimated prevalence of disorders
Fortunately, digital health has arrived in the veterinary sphere and should provide, for the first time, comprehensive estimates of the prevalence of disorders.
Paul is the Chairman of VetCompass Australia, based on the highly successful UK VetCompass which he helped establish ten years ago. It is the first Australia-wide surveillance system that collates clinical records of companion animal diseases and treatments.
Bringing together Australia’s seven veterinary schools, VetCompass Australia collects the clinical records of hundreds of vets across the country for researchers to interview. Analysis of these records will reveal trends in the prevalence of inherited and acquired diseases, identify effective treatments, and help veterinarians and breeders improve the quality of life of dogs.
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The vision for this surveillance system is that it will one day provide real-time data on the prevalence of every known disorder and show the effectiveness of various control strategies. Real-time data will also sound the alarm about clusters of new disorders as they emerge.
Complementing VetCompass, MyBreedData, a Finland-based website, collects genetic test results from large numbers of dogs to identify mutations known to cause particular hereditary disorders. Among other things, this information provides warning signs as to which breeds contain which harmful mutations.
What about hybrid vigor?
Hybrid vigor for a particular trait is the extent to which, on average, puppies resulting from mating a purebred female of one breed with a purebred male of another breed are better for that trait than the average of the two parent breeds for this trait. trait.
Evidence from other species suggests that hybrid vigor in dogs may occur to a limited extent in traits related to health, well-being, and fitness for purpose. The greater the genetic difference between two breeds, the greater the hybrid vigor should be in the first generation offspring between those breeds.
Specifically, first-generation offspring are unlikely to develop recessive disorders present in only one of the two parent breeds. On the other hand, they can obviously develop inherited disorders present in both parent breeds, which is often the case with disorders like hip dysplasia.
It is important to note that selection beyond first generation crosses reduces hybrid vigor and releases unpredictable variation. This is good news for traditional stud breeders, as it means that the most sought-after hybrids are the descendants of two thoroughbreds, rather than those bred afterwards.
Mixed-breed (or “brand”) dogs aren’t new: The Kennel Club has been registering them for over 50 years. Unfortunately, most peer-reviewed studies of canine crossbreeding do not allow us to estimate true hybrid vigor, simply because they do not report the parentage of mixed-breed dogs.
Fortunately, obtaining evidence of actual hybrid vigor in dogs should be relatively simple: it is sufficient that veterinary records include the parentage of mixed-breed dogs, when known.
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The information collected by VetCompass and MyBreedData will provide a solid foundation for prioritizing research and control programs for inherited disorders within breeds. It also has the potential to shed valuable light on the extent to which hybrid vigor exists in dogs. Armed with this information, breeders will be able to combine new technologies with the skills of traditional dog breeding to breed dogs that are more likely to look good, be healthy and thrive in the niches we give them. propose.