Friday, November 30, 2012

Achieving Genetic Diversity within the Pure Bred Dog Community

     There is a not so silent war raging between pure bred dog breeders and so called designer dog breeders.  It is a war of words and it gets nasty.  This post is not about creating a new trendy dog breed for financial gain.  It is about the health of dogs.  All dog breeds, almost without exception were yesteryears designer dogs whether pure bred dog breeders want to admit it or not.  The dog genome has been mapped.  Dog breeds fall into five different clusters, the vast majority of breeds falling into just one cluster.  What does this mean?  All these breeds have common ancestors.  One could illustrate it by thinking of dogs as being a basic white cake.  To make the cake more interesting one person might add chocolate frosting and roses, another strawberry frosting and gumdrops, still another chooses lemon frosting and orange peals.  All three cakes taste different but at the heart they are still just white cakes.   What one sees as breed diversity is simply the outside phenotype (the frosting) with a few behavioral modifications (the decorations.)
     It is only in the last century that we have fallen into the mystic of the pure bred dog.  It is fashionable to say I own a registered Golden Retriever or Border collie or Pekinese or now the Shih Poo.   The genetic problems seen today in pure bred dogs will appear in the designer dogs if their breeders go down the same path purebred dog breeders have been following for years.  Closed stud books lead to loss of genetic diversity and major behavioral and physical problems.  What does loss of genetic diversity mean and how can this trend be slowed or even eliminated?
     One study of genetic diversity of pure bred dogs using pedigree analysis found evidence of inbreeding in 9 of the 10 breeds sampled and the loss of genetic diversity >90% over six generations. million dogs were studied during this research.  Part of the researcher’s conclusion states “On the basis of these results, we concur with LEROY et al. (2006) that remedial action to maintain or increase genetic diversity should now be a high priority in the interests of the health of purebred dogs. Possible remedial action includes limits on the use of popular sires; encouragement of mating’s across national and continental boundaries, and even the relaxation of breed rules to permit controlled outcrossing.”[i]  What does this study imply? 
      One of the arguments among pure bred dog breeders is that there is plenty of diversity out there because of population numbers.  But do x number of dogs equal diversity?  No.  It doesn’t matter if here are 50 dogs in the gene pool or one hundred thousand if the genetically the dogs are closely related. It is not distance or numbers which adds diversity. million dogs is a lot of dogs and yet inbreeding was present in almost all of the pedigrees.  What does this mean?
     For pure bred dogs and their breeders it means the animals are more prone to genetically based health issues and a drop in fecundity. Closely bred dogs have more difficulties breeding and in producing viable offspring.  What then is the answer?  Controlled outcrossing. Two simple words that for pure bred dog breeders and most kennel clubs are considered dirty, sacrilegious, and worth starting at least a verbal battle over if not a physical one.  Why is controlled outcrossing sinful in the sight of breeders? And what can advocates of this simple effective means of breathing new life into what some scientist believe is on the road to extinction, the pure bred dog?
     Breeding dogs as it is practiced today involves inbreeding, line breeding and outcrossing within the breed itself.  To illustrate let’s put humans in the place of dogs for a moment.  Inbreeding is breeding two closely related individuals together such as mother to son, father to daughter, or brother to sister.  Genetic testing has revealed a five generation family tree for King Tut, with brother to sister couplings.  Two still born fetuses are believed to be Tut’s daughters by his half-sister. Both fetuses showed genetic abnormalities.  Tut suffered from a genetic bone disease which entails low blood supply to the bones and he had a club foot.  Continued inbreeding within this royal line led to much suffering and eventually the loss of viable offspring.  This is one example of what happens in humans when inbreeding is followed consistently.
     Line breeding entails breeding related individuals such as cousins.  The male descendants in the line of Queen Victoria of England suffered from Hemophilia B.  DNA testing of the recovered bone fragments of Alexei, the son of the last Tsar of Russia revealed the child suffered from the genetically inherited disease. Many of the ruling houses of this era were related to Queen Victoria and so the disease spread throughout these lines.  For example the three main players of WWI, King George V, Kaiser Wilhelm II, and Tsar Nicholas II were all first cousins.  Victoria was called the grandmother of Europe.  Her struggles to bring the ruling houses of Europe into one family through line breeding ultimately affected the health of them all.
     These examples of inbreeding and line breeding in humans are presented to demonstrate that where humans are concerned most individuals and probably 99% of pure bred dog breeders would agree that inbreeding in humans is a bad thing.  Incest is forbidden across most cultures.  Yet the same individuals fail to connect that continued line and inbreeding in dogs produces the same results seen in humans.  Genetically all species reproduce in the same manner whether they are human animals or canine animals.  What is the answer?  Most breeders would agree that outcrossing and genetic testing within the breeds will help eliminated inherited deficiencies? 
      This is not entirely true.  Pure bred dogs by definition are a closed gene pool.  There are no true outcrosses within breeds because as the above research shows, purebred dogs are related genetically.  Breeders are in fact line breeding when they think they are out crossing.  Most breeds can be traced back to a handful of distinct individuals.  Eliminating genetic carriers of disease does nothing more than decrease the gene pool still more.  The only way to introduce genetic diversity into these closed groups is through controlled out crossing.  What is controlled outcrossing?
     Controlled outcrossing is the breeding of a line of pure bred dogs to individuals of another breed (or a mixed breed dog.)  Doesn’t this make the offspring mutts?  Here’s the issue that has kept stud books closed to the determent of dogs and it is about exclusivity.  It is a form of eugenics.  When practiced within a human society it led to the atrocities of Nazis in WWII.  It was designed to purge inferior elements from the human race, the mutts of human society.  Rather than detrimental controlled out crossing or heterosis as it is called consistently produces healthier individuals with increased vigor and increased fecundity.  The old adage that mutts make better pets from an overall health point of view is probably true.
     What Basenji breeders did in in the 1970s and 80s, whether they considered it as an experiment in heterosis or not, is a good example of controlled outcrossing.  They went to Zaire and collected dogs to bring back to the United States including one bitch that was already in whelp.  Careful crossing between these African imports and American bred Basenjis began.  Were these individuals lovely examples of what Americans think of as the ideal basenji?  No, but with time and effort the individual offspring of these matings conformed more to the standard. This is what one individual reported on the results of this controlled outcrossing:
 Of the approximately 260 Basenjis having an Avongara or Esenjo in their pedigree, all have tested as outstandingly healthy! No other line has been so intensely tested as these two, and no other line has generated so many healthy animals. As per a list of the US Basenji Club:
Fanconi 0
Dysplasia 1
Fanconi, PRA or IPSID when crossed with a purebred 2

With results like these, there’s really little left to discuss!
Author's Beloved Basenji, Pharlap
These crosses have been shown to be a complete success for the Basenji breed!”[ii]
This is controlled outcrossing and it works.
     What will it take to improve the lives of pure bred dogs?  It will take courage on the part of breeders.  It will take thinking outside of the box of popular rhetoric of what is or is not a pure bred dog.  It will take effort as it did with the dedicated Basenji breeders who spent years working to improve the phenotype of these crosses.  What it produces is a stronger healthier gene pool with added vigor and fecundity.


[i] F. Calboili, J Sampson, N Fretwell, and D. Balding, “Population Structure and Inbreeding from Pedigree Analysis of Purebred Dogs,” Genetics, May 2008, 179, 593-601.
[ii] “About the African Stock Project,”, accessed 11/30/2012.

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