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Kennel Club Breed Population Analyses tool

Gleroy

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thumb_blog-0856212001444235632_1.thumb.jA few weeks ago, Tom Lewis and his colleagues published what is, up to now, the largest pedigree analysis regarding to the number of populations analyzed, with the 215 breeds recognized by the UK Kennel Club. In the same time, individual breed reports have been made available in the KC website, with accessible infographics on the phenomena behind inbreeding such as effective population size or popular sire effect. Just for this, this work should be saluted, and we can hope that other national kennel clubs will follow this example. Actually, even people most critical to the KC breeding policy have recognized that it should be congratulated for this study. Yet it has also been stated that the global message of the paper, indicating that “initial excessive loss of genetic diversity has latterly fallen to sustainable levels” was probably too much optimistic. After all, it can be indeed considered that 25% of breeds with effective population size under 50 is not so sustainable.

 

Is it so? And actually what can be deduced from the paper and the analysis?

 

 

Evolution of inbreeding

 

From far away, the most striking result is related to this stabilization (and in several case decrease) of inbreeding occurring in most breeds since the years 2000. As a consequence when computed on recent years, effective population size have increased in multiple breeds. Actually, in case when inbreeding was decreasing, it was not even possible to compute effective population size. But does this really mean that inbreeding stopped to increase? Probably not. First because, in theory, inbreeding can only increase. As the number of generations increases, more and more ancestors in common between both parents will be found, adding their contribution to overall inbreeding. Therefore, as underlined by the authors, this change in inbreeding trend is probably largely explained by the fact that importation increased largely in the years 2000, after relaxation of UK quarantine law. This has probably led to the registration of foreign dogs, with limited pedigree knowledge, and therefore supposedly unrelated. In practice, it is certain that on the beginning, those dogs were less related that the average of national dogs. Yet, after a few years of importations, it is also probable that imported dogs are actually bringing more inbreeding that what is hypothesized based on their limited pedigree knowledge. It could therefore have been interesting to correct genetic parameters such as effective population size by considering this pedigree knowledge.

 

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But is this so simple? Actually, the study of Lewis also provides some results indicating that the recent evolution of inbreeding could be also linked to real inbreeding reduction, although temporary. Indeed, inbreeding is the sum of the reduction of within population genetic variability (which can only decrease), added to factors inherent to the population, such as existence of subpopulations, or mating between close relatives. The extent of inbreeding due to population structure can be assessed by comparing population inbreeding with the degree of coancestry between individuals, or between their parents. This is what Lewis and his colleagues have done, when referring to expected inbreeding. In most of their breeds, real observed inbreeding appears larger than expected one, indicating existence of substructure. Yet in the majority of cases, this difference has clearly decreased over the last years, which probably indicates that breeders have improved their breeding practice, eventually toward less mating between close relatives.

 

Reduction of popular sire phenomenon

 

One of the interrogations that I have with this paper is related to the fact that they may have been some change in the use of popular sires. Indeed, a more balanced use of reproducers is expected to reduce (but not inverse) the increase of inbreeding. However, as previously stated, it is difficult to identify such tendency on the basis of inbreeding evolution alone, as it is already impacted by importations and change of substructure. As suggested by the authors, the analysis of the progeny distribution overtime may bring some information on this issue. Yet it has to be stated that this distribution is highly dependent on breed demographics: in a population with 100 annual births, it is quite easy to have a sire producing 25% of the puppies; it is hardly possible in a population with 10,000 births. In most of the breeds studied, registration have either largely increased or decreased over years, so the direct interpretation of progeny distribution evolution should only be made in breeds with stable registrations. Eventually a statistical analysis of the results over the 215 breeds could bring interesting results on this evolution.

 

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So, on my point of view, if there is still effort to be made in the management of genetic variability within UK dog breeds, the article point out some clear progress. Increased importation probably brought some variability within national population, even if those improvements should not be overestimated: imported dogs of yesterday are probably related to imported dogs of today. They have been also probable improvements in mating practice, which is also good news. It is rather difficult for me to identify if there has been change in popular sire phenomenon, and further analysis could bring information on this. In term of communication, it is highly appreciable that messages on better management are brought to the breeders.

 

 

References:
Lewis T.W., Abhayaratne B.M., Blott S.C. (2015) Trends in genetic diversity for all Kennel Club registered pedigree dog breeds.Canine Genetics and Epidemiology20152:13

DOI: 10.1186/s40575-015-0027-4

 

Credit picture: I. Horvath

 


 



4 Comments


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Thank you Gregoire for this blog post.

 

This stabilization of inbreeding was visible also in my study on Tollers and Lancashire Heelers, in which the worldwide populations were analyzed and thus no foreign dogs existed. I think that a change in breeding practices could be the reason for the stabilization.

 

It is good to have pedigree analyses for as many breeds as possible, and I congratulate Tom as well, for this well-made report based on a huge amount of breeds and data. But I just cannot keep myself from thinking about all the widely spread, breed-specific hereditary problems. It does not matter much whether we have an effective size of 50 or 100, if the breeders are already in trouble when trying to find healthy dogs for breeding.

 

In Finland we are discussing different possibilities to increase genetic variation and number of breeding dogs in pedigreed breeds. It is certain that in the future we need more open registries and also breed crosses in many breeds. At the moment the Finnish Kennel Club's registry is open for example in the Lancashire Heelers, allowing us to take good landrace individuals into the appendix of our register and use them in breeding as well. We are also discussing about being a kennel club for all dogs, not just purebred dogs.

 

 

Edited by Katariina Mäki

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Thanks for your feedback !

I would tend to think that one good judge on this would be the comparative increase of kinship (their expected inbreeding). If kinship also stabilized I would bet more on importations, otherwise it could be indeed change in breeding practice.

 

In the two examples here I would guess you are probably right. In other cases (Bearded collie http://www.thekennelclub.org.uk/media/685423/bearded_collie.pdf) I would not be so sure.

 

Fully agree also that the links between effective population size and breed health should be clarified. That does not mean it has no interest wink.png .

 

Same thing for outcrossing: the more we will have of successful examples, the more people will be open to it as a tool. 

 

 

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Yes I saw this amazing effort on the KC site, and we posted an article on IPFD pointing to it at: http://dogwellnet.com/content/health-and-breeding/breeding/breeding-for-health/population-breed-level-approach/the-kennel-club-breed-population-analyses-r303/...

May I, should we point to this blog discussion in the IPFD article?

I wondered what a breeder might "do" with this info - I think it is realistic to pose a casual question a breeder might ask! "That's nice, but what does it mean to me?". I also wondered about the statement made under The Bernese Mountain Dog:

"Comments

Unusually, the rate of inbreeding for this breed between 1980 and 2014 is negative. This means that genetic variation within the breed appears to be increasing (possibly through the use of imported animals).
There appears to be extensive use of popular dogs as sires in this breed (the ‘tail’ of the blue distribution in figure 3).
It should be noted that, while animals imported from overseas may appear completely unrelated, this is not always the case. Often the pedigree available to the Kennel Club is limited in the number of generations, hampering the ability to detect true, albeit distant, relationships."
 
How related are the imports? hmmmmmmmmmmm..........  :-)

 

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Of course you can link it :) .

I think for breeders it may provide useful information on their breeds, the problem being that interpretation may be sometimes difficult. Information of progeny distribution can give idea on what efforts should be made to have a more balanced use of reproducers at the kennel scale. If the sires of a given breeders provide on average 40 dogs, while the mean is the breed is 15, maybe the breeder should think about enlarging the number of sire he use for instance.

 

In the case of Bernese Mountain Dog, the impact of importations is obvious for me, as both observed and expected inbreeding are decreasing. Indeed, it is probable that especially after several generations of importations, there is a bias in the absence of kinship measured in the freshly imported dogs. 

 

 

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