Is selective breeding reducing the dog gene pool?

Many dog breeds today show little resemblance to their ancestors from the pre-dog show era (just over 100 years ago), with many modern day dog breeders selecting individual animals for their asthetics at the detriment of temperament, or welfare: with abnormal temperament reported as among the top 12 important issues by breeders of pure bred dogs (Beaver 1999). The genes responsible for genetic diseases are often recessive, needing two recessive genes to come together to display the trait; inbreeding by using mother to son, sister to brother mating, used to achieve the ‘perfect look’, increases the likelihood that genetic abnormalities will be displayed in the offspring.

Scott and Fuller (1974) suggest that by paying attention to one narrowly defined category, for example ascetics, in the breed standard, the result will almost inevitably lead to the selection of various undesirable characteristics, albeit by accident. They suggest that including regulations relating to health, behaviour, and focusing on hybrid vigour (by having a large number of parent strains to choose from), within the breed standard, will ultimately produce superior animals, as opposed to what Scott and Fuller term “freakish traits” for example the Bulldog’s head which they cite as inferior to the natural confirmation.

Paedomorphosis (the retention of juvenile characteristics into maturity) is actively sought by many breeders, for example the Cavalier King Charles Spaniel, and by actively selecting for physical traits such as a larger eye to face ratio, the resulting smaller cranium has less room to accommodate the brain, leading to a painful condition where the hindbrain prolapses out of the back of the skull, and the well-documented condition Syringomyelia (cyst on the spine) which affects 25% of pedigree Cavalier King Charles Spaniels by 12 months of age and up to 70% by 6 years of age (Parker et al 2011). Asher et al (2009) suggest this frequency may be as high as 50% in other small-cranium breeds, and that at least one heritable defect, related to breeding for physical confirmation, could be found in each of the top 50 pedigree dog breeds in the UK. To the other extreme large giant breeds are predisposed to conditions such as hip or elbow dysplasia, brought about by selectively breeding for large body size and fast-growth; while Summers et al (2010) report their findings show the nervous system as the most commonly aversively affected body system, in pure bred dogs.

In examining pedigree dog breeding in the UK Rooney (2009) gives numinous examples of exaggerated anatomical features, and the effect these exaggerations are having on the animal’s quality-of-life.  Increasing body weight in giant breeds has amplified their health problems, and led to a dramatically reduced lifespan for individuals over 30 kg (an average dog weight), with breeds like the Great Dane living on average only 7 years while a Toy Poodle can average over 14 years, one reason for this disparity is the disproportionate incidence of cancers, particularly osteocarcoma (bone cancers), in the act of selectively breeding for size (Kraus 2013).

Many physical attributes that have been selectively bred for, mainly through mother to son and brother to sister mating, has inadvertently led to behavioural issues:  in the German Shepherd, breeding for the sloping spine and a lack of genetic diversity through in-breeding has resulted in increased nervousness and fearfulness, which over a short time period has changed the breed’s characteristics from dependable, reliable, guard dogs to fear biters.  The exception to this is the black long hair phenotype, which is less likely to be fearful; these individuals also lack the breed standard’s sloping spine, it would seem reasonable to infer that selective breeding for the sloping spine may have led to temperament changes. Another breed with recognised behavioural issues inadvertently caused by seeking a certain phenotype is the Cocker spaniel, some individuals experience an uncontrollable fighting trait, which veterinarians term an avalanche of rage; this is associated with breeding for the solid red and gold coloured individuals whereas solid black individuals rarely exhibit it (Rooney & Sargan 2012). While the rage syndrome experienced by Cavaliers is coincidental, one breed which has been specifically bred to alter its behaviour is the Border Collie, breeding to “show eye” (stare), has led to an increase in stereotypical behaviours such as staring at blank walls or shadow chasing, which Beaver (1999) suggests is a stress relieving measure.

The rapid breeding cycle of the domestic dog means that genetic abnormalities leading to behavioural issues can be compounded, or improved in only a few generations as demonstrated by Belyaev’s experiments with foxes. In his experiments he sought to change the temperament of the foxes, and extended the socialisation period to make them easier to handle. Belyaev chose only the friendliest of the foxes and bred these, over about 40 generations the fox’s temperaments improved and a side effect was a change in coat colour from black to piebald, along with a reduction in cortisol levels that measure the animal’s stress levels; however when Balyaev’s experiments ended and natural selection regimes returned the foxes reverted to their usual temperament and colour within only a few generations (American Scientist 2013).

We can see that in striving for the breed standard we have altered many breed’s genetic make-up, and subsequently it’s physical and behavioural characteristics, and that this isn’t always the best outcome for the dog. If the emphasis on aesthetics continues, there is little chance that the health and behavioural welfare of pure breeds will improve; but it is also possible to reverse these disadvantages is a short time frame with the introduction of new genetic material, and the will to change.

References

American Scientist (2013) Early Canid Domestication: The Farm-Fox Experiment Downloaded March 2013 from http://www.americanscientist.org/issues/pub/early-canid-domestication-the-farm-fox-experiment/1

Asher, L. D, Summers.G, McCreevy. J.F, Collins. P.D (2009). inherited defects in pedigree dogs. Part one: disorders related to breed standards. The veterinary Journal, vol. 182 pp. 402 – 411.

Beaver, B. V. (1999). Canine behaviour: A guide for vetetinarians. Saunders.

Kraus,C. (2013). Why small pups outlive large dog breeds. Livescience.  Downloaded March 2013 from http://www.livescience.com/27676-why-small-pups-outlive-large-dogs.html.

Parker, J.E, Knowler, S. P, Noorman, E, Jeffery, N. D. (2012) Prevalence of Syringomyelia in Cavalier King Charles Spaniels. Veterinary record. 186 pp 667-669

Rooney, N.J. (2009) The welfare of pedigree dogs: cause for concern. Journal of veterinary behaviour, vol 4 pp 180 -186

Rooney, N.J, Sargan, D. (2012) Pedigree dog breeding in the UK: a major welfare concern. Downloaded March 2013 from: http://www.rspca.org.uk/ImageLocator/LocateAsset?asset=document&assetId=1232712491490&mode=prd

Scott, J.P., & Fuller, J.L. (1974). Genetics and the Social Behaviour of the Dog. The University of Chicago Press, Chicago.

Summers. J. F, Diesel. G, Asher. L, McGreevy P. D, Collins. L, M. (2010) Inherited defects in pedigree dogs. Part 2 Disorders that are not related to breed standards. Veterinary Journal Jan 183 (1) : 39-45.