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To what extent should dog breed purity be pursued?
Since the first domestication of the dog, their species have now come to be the most morphologically diverse in the world (Gross 2010). From their ancestor, the wolf, to the hundreds of breeds present today, humans have utilised many methods to achieve this incredible feat. Now, the purpose behind breeding has transitioned, resulting in a change in the appearance of the dogs themselves. From what was a means to create a type of dog more skilled for a certain function, such as hunting, guarding or herding (Farrell et al. 2015), towards being used in the pursuit of cosmetic perfection, dog breeding is now considered a form of ‘art’. (https://www.akc.org/expert-advice/dog-breeding/the-art-and-science-of-breeding-better-dogs/).
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In fact, the definition of a breed even differs from the perspective of a geneticist to that of a breeder. From the geneticist’s point of view, ‘a breed is a group of dogs with defined characteristics which exist in a closed gene pool’ (Starling, 2007). However, the breeder will define it as ‘a group of dogs from known lineage of similar dogs, with an agreed set of physical and behavioural attributes which (preferably) breed ‘true’ ie reliably replicate these characteristics in their progeny’ (Starling, 2007). It should be clear that the breeder puts the emphasis on the lineage, and the ability of the dog to pass down characteristics reliably. They have become obsessed with the ‘pureness’ of their dogs’ genes, and now resort to purposeful inbreeding in order to eliminate the addition of other alleles which may produce undesirable traits, that can be considered to be a ‘contamination’ of the lineage. This was the start of the pursuit of the purebred pedigree dog breeds, which are heavily regulated regarding size, shape, and colour as well as many other characteristics. Such intentions in breeding, encouraging extensive practises of inbreeding and artificial selection, has caused devastating results. Pedigree dogs now suffer from more than 500 types of genetic disease (Arman, 2015) that they inherit just as reliably as the morphological traits that they have been bred for.
Carefully planned breeding has been the practise behind the formation of dog breeds, but there is much more to this than one can imagine. First, to form a breed, individuals with desirable visual characteristics are selected, then isolated sexually from other dogs, to create an artificial bottleneck situation. These individuals are bred together, and from their offspring, only those with the most desirable and exaggerated traits are selected to be the founding stock, which go through much inbreeding across the generations (Arman, 2015). The problem with inbreeding is that such restricted, or at times, nonexistent gene flow reduces genetic variation (Wüster 2008) within the breed population. This has serious consequences for the population, as the breeders’ intentions to fix certain alleles of wanted phenotypes by increasing the allele frequency close to 100% results in similar results for alleles with undesirable effects, such as disease. Reduced genetic variation also introduces the threat of increased risk of extinction, as the population has a very low chance of possessing an allele which will provide resistance against new disease and changing environmental pressures (Lorimer 2007). In addition, as the rate of homozygous alleles increases, inbreeding depression can almost certainly be observed to occur. Inbreeding depression is a phenomenon of a lowered ability to survive and reproduce for a population (Wüster 2008). It can encompass a wide range of effects such as reduction of litter size and longevity (Leroy et al. 2015). This occurs as natural selection is not able to select against such alleles reducing fitness and remove them from the population, due to the selection factor now being the breed standards of kennel clubs and the eyes of humans deeming phenotypes expressed by sometimes neutral, but at times harmful alleles to be most desirable. Defective alleles are most often recessive, and are not expressed in heterozygous form, called deleterious recessive alleles (Charlesworth and Willis 2009). However, because of excessive inbreeding, their frequencies within the populations slowly increase, resulting in individuals with a homozygous set of these deleterious recessive alleles, in which the phenotype corresponding to the alleles are expressed, most likely as a disease or a disability. The number of such individuals then keep increasing as further levels of inbreeding are carried out, and soon more of the population expresses this trait. So it can be seen that reduced genetic variability and increased homozygosity does not have a positive impact on a population.
As it can be easily expected, purebred dogs have a higher rate of genetic disease than cross breds, which still have some level of genetic variability (Calboli et al. 2008). It has been found that purebred dogs have significantly higher rates of 10 genetic disorders than cross breds, which include aortic stenosis, atopy/allergic dermatitis, gastric dilatation volvulus (GDV), early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, hypothyroidism, intervertebral disk disease (IVDD), and hepatic portosystemic shunt (Farrell et al. 2015). Orthopedic diseases such as hip dysplasia and elbow dysplasia which are highly represented in large and stocky breeds such as the American Bulldog and Saint Bernard are results of selection of morphological features, in this case the ‘stockiness’, which correlates with the selection of genes that predispose the dogs to these diseases (Boyko et al. 2017).
Diseases relating directly to the exaggerated features of purebred dogs are also observed, perhaps the most prominent being the Brachycephalic Airway Syndrome in Brachycephalic breeds, which include the Pug, French Bulldog and Boston Terrier among others. For these dogs, the abnormal upper airway anatomy due to the shortened snout produces complications in breathing, including stenotic nares, an elongated soft palate, a hypoplastic trachea and everted laryngeal saccules (Bellumori et al. 2013). These conditions, whether individually or combined, cause major discomfort and even fatalities for the affected (Roedler et al. 2013). Medical management such as oxygen therapy and medication cannot correct the underlying abnormalities, and surgical removal of tissue in the airway is the only possibility to provide relief from extensive breathing difficulties (Bellumori et al. 2013). Furthermore, the dogs suffer from a prolonged recovery time from physical activities, significant heat sensitivity and various sleep problems (Packer et al. 2015). They are even vulnerable to suffocation during sleep, as muscular relaxation narrows the respiratory passages (Koch et al. 2003). Not only this, but the brachycephalic breeds are unable to give birth naturally due to large skull sizes and comparably lesser pelvic diameters, and cesarean section is necessary for more than 80% of the Bulldog, French Bulldog and Boston Terrier (Adams and Evans 2010).
These breeds are not the only ones to suffer from conformation related diseases, as toy and small breeds such as the Cavalier King Charles are prone to disease such as Syringomyelia, a condition where high pressures of cerebrospinal fluid result from the small size of the skull being unable to accomodate the brain (Hechler and Moore). This condition accompanies severe, persistent pain described as a burning sensation (Poma and Wolfe). Chiari-like Malformation, the mismatch in size between the brain and the skull, is observed in 95% of the Cavalier King Charles Spaniel breed, and of these dogs, Syringomyelia is present in 50% (Poma and Wolfe). Non conformation related disease and disease resulting indirectly from morphologies also account for a major portion of the dog population’s suffering. Such is the Dermoid Sinus common in the Rhodesian Ridgeback breed, in which affected dogs develop a sinus tract in the dorsal cervical area from the skin to depths of variability, putting them at high risk for infection, especially dangerous if the sinus leaves the cervical vertebra exposed (Filho et al. 2008). The disease is thought to be caused by dysregulation of one or more of three fibroblast growth factor genes, responsible for the formation of the dorsal hair ridge, meaning that the ridge formation predisposes all ridgebacks to the disease (Hilbert 2005),(Andersson and Hilbert 2006). However, the ridge is considered to be the dominant feature characterising the breed, and must therefore be present in all individuals. However, it was the ridgelessness that caused higher amounts of deaths for the Rhodesian Ridgebacks. The ridgeless puppies were undesirable and were therefore culled at death. Of the 10% of ridgeless puppies reported, 68% were euthanised (Moritz 2006). Yet, the development of the ridge is continued to be seen as imperative in the Ridgebacks, and the breed standards of the American Kennel Club reveals this: “The hallmark of this breed is the ridge on the back which is formed by the hair growing in the opposite direction to the rest of the coat. The ridge must be regarded as the characteristic feature of the breed.” – (http://images.akc.org/pdf/breeds/standards/RhodesianRidgeback.pdf)
It is known that there is at least one conformation related disease present in each of the top 50 breeds, and a total of 84 disorders resulting directly or indirectly from aspects of their conformation (Asher et al. 2010). A total of 312 non conformation related diseases were identified in dogs, and of these 71% are autosomal recessive (Asher et al. 2010), meaning that they can only develop if two copies of the recessive genes responsible for the disease are present. This evidently shows the extreme levels of inbreeding that must have occurred for such high levels of recessive genes to be present in the breed populations. These diseases have largely negative impacts on the quality, and even quantity of lives for the affected dogs, and are being observed at alarming rates in many dog breeds. Moreover, the welfare of dogs as our companions is under serious concern.
It is to be wondered why pedigree dogs are still pursued with such passion as seen in the hundreds of thousands of dogs registered with each kennel club. Such pursuit of a seemingly fruitless endeavour has even been linked to the theory of eugenics (Harrison 2008) in the investigative documentary ‘Pedigree Dogs Exposed’ broadcasted by BBC. In the film, it is suggested that the human fancy of superiority has been the cause for the pursuit of pedigree dogs with ‘pure’ genes, similarly to the eugenicist ideal behind royal bloodlines maintained through incestuos marriages or the Holocaust. It was in the Victorian era that the breeding of dogs began to be considered a sport, and the pedigree dog a symbol of status, becoming increasingly popular (Farrell et al. 2015). The isolation of populations and the breeding methods practised since this time was the beginning of the dog breeds in our world today. The pedigree dog may be desired by some for the definite way of knowing what the dog will look like as an adult, unlike the crossbreeds. However, with the certainty of morphology comes the certainty of genetic diseases associated with most breeds.
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More appropriate breeding practises leading to the birth of healthier dogs include maintaining balance of the number of sires and dams, avoiding inbreeding altogether, abstaining from repeat breedings, ensuring sibling contribution and maintaining diversity by paying attention to the number of unique ancestors (Braggs 2009). Kennel clubs have responded to the increasing number of research into the health of pedigree dogs and investigations into the world of dog shows by including recommendations for testing parent dogs before breeding to find genetic diseases they may carry, and to use the COI (Wright’s Coefficient of Inbreeding) calculator to reduce high levels of inbreeding which may result in inbreeding depression.
However, existing breed standards of Kennel Clubs continues to put these dogs at increased risks for conformation related diseases (Asher et al. 2009). Kennel Clubs responsible for such risks do so by setting breed standards and regulations for dogs that further encourage exaggerated morphologies detrimental to the dog’s health, which in turn calls for breeding practises increasing the rates of hereditary genetic disease. Stated in the breed standards of the Bulldog, from the American Kennel Club is the quote: “The face, measured from the front of the cheekbone to the tip of the nose, should be extremely short, the muzzle being very short”. – (http://images.akc.org/pdf/breeds/standards/Bulldog.pdf) This was from the approved breed standards revised in 2016, well after much research and inquiry had been conducted into the matter of BAS in Brachycephalic breeds. Such standards for the ideal morphology of certain dog breeds pressures for more exaggerated features favouring conformation related disease, and encourages methods of breeding such as inbreeding, linebreeding, pedigree breeding and breeding to a popular sire, which are all forms of artificial selection resulting in reduced genetic variability and increased genetic homozygosity of alleles. As discussed in the first section, this type of restricted gene flow within a population has disastrous effects, evident in the examples of diseases discussed. Breed populations are further impacted in ways such as the phenomena regarding the loss of over 90% of unique genetic variants in the gene pool of the seven most popular dog breeds, which only took place over six generations (Balding et al. 2008), leaving the dogs more vulnerable to new diseases and the changing environment.
The welfare of the dogs themselves is also a factor in need of consideration. It is obvious that the health of the dog should be put before any typology desired by humans. This provokes the question of whether domestication itself should be acceptable, as dogs show retardation in foraging and hazard-avoidance behaviours (Fitch et al. 2014), which relates to the significant reduction in the brain to body weight ratio in domesticated dogs as compared to wolves, an occurrence demonstrated in all cases of domestication, examples being pigs and horses. (Fitch et al. 2014).
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