View Full Version : Study on inbreeding in UK dogs

19th August 2008, 01:29 PM
From Imperial College London vet school -- one of the co-authors is, ahem, the UK KC Club's own geneticist, Jeff Sampson. I wonder what his advice is to the Kennel Club then?

From: http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_15-8-2008-12-22-2?newsid=42674

Extent of inbreeding in pedigree dogs revealed in new study

Study explores inbreeding, which puts dogs at risk of birth defects and genetically inherited health problems

By Laura Gallagher
Friday 15 August 2008

The extent of inbreeding in purebred dogs and how this reduces their genetic variation is revealed in a new study by Imperial College London researchers. Inbreeding puts dogs at risk of birth defects and genetically inherited health problems.

Particular dog breeds are believed to be prone to particular health problems and birth defects. For example, Dalmatian dogs are predisposed to deafness, many Boxer dogs have problems with heart disease, and disproportionate numbers of German Shepherd dogs have an abnormal developmentof the hip joints known as hip dysplasia.

Inbreeding in pedigree dogs arises because certain dogs, prized for exhibiting the characteristics desirable for that breed, are used to father many litters of puppies. When dogs from these litters come to be mated, some will be paired with dogs having the same father from other litters. Over generations, more and more dogs across a particular pedigree are related to one another and the chances of relatives mating increase.

Recessive genetic variants only have adverse health effects such as deafness when an individual carries two defective copies of the gene. If a popular sire carries just one defective copy, he will not show the problem himself and nor will his puppies. However, the defect may become common in later generations if his grandpuppies and great grandpuppies are mated with each other, rather than introducing new genetic traits by breeding outside their relatives.

Although the problems associated with inbreeding have been known for many years, prior to the new study it had not been systematically measured. For this study, researchers from Imperial used mathematical modelling to analyse how dogs were related to one another within ten different dog breeds including the Boxer and Rough Collie.

They looked at the parentage of eight generations of dogs, using records collected from 1970 to the present day by the UK Kennel Club.

The researchers' analysis showed that, for example, Boxer dogs were so closely related to one another and had such little genetic variation between them that genetically, 20,000 dogs looked like a population of about 70. In the Rough Collie breed, 12,000 dogs looked in genetic terms like a population of about 50.

Such small effective population sizes mean that the chances of a dog breeding with a close relative, resulting in birth defects and genetically inherited health problems, are high. The researchers argue that those involved in breeding dogs should encourage breeding from a larger pool of potential mates in order to create greater genetic variation and lessen dogs' chances of inheriting genetic disorders. They suggest measures such as limiting how many times a popular dog can father litters; encouraging mating across national and continental boundaries; and relaxing breed rules to permit breeding outside the pedigree.

Professor David Balding, the corresponding author of the research from the Division of Epidemiology, Public Health and Primary Care at Imperial College London, said: "The idea that inbreeding causes health problems in particular dog breeds is not a new one, but we believe ours is the first scientific study to explore this issue and analyse the extent of inbreeding in a systematic way, across many breeds. We hope that following our work, dog breeders will make it a high priority to increase the genetic diversity within different breeds. Otherwise, we will see growing numbers of dogs born with serious genetically inherited health problems."

The researchers carried out their analysis as part of an effort to explore how understanding disease in dogs can help inform research into human disease. The research was funded by the Biotechnology and Biological Sciences Research Council.


Further information about the research is provided in the study, which is published in the journal Genetics:

"Population structure and inbreeding from pedigree analysis of purebred dogs," Genetics, 179(1): 593–601, 2008. doi:10.1534/genetics.107.084954 Calboli FC , Sampson J, Fretwell N, Balding DJ

More here (http://coldwetnose.blogspot.com/2008/08/pedigree-dogs-exposed.html).

19th August 2008, 08:11 PM
I kick around on the CanGen site as well, and learned of this study when it came out in May.

What is very upsetting is that this is about all the breeds. Of the 10 breeds studied, only the Labrador, with its HUGE population, has enough genetic variation to represent more than 100 dogs.

A full eight out of the 10 breeds studied had effective population sizes of between 40 and 80. If you understand population genetics, even a little, this is a disaster waiting to happen. Zoologists attempt to keep even their rarest breeds with an effective pop. size of over 200 in hopes of avoiding genetic difficulties. In most natural populations, even smaller ones, the size is well into the many thousands. You can find reference to the magic "200" number here.


I have asked what the effective population size of Cavaliers was, and was told 72, but at the time did not think to ask for the reference information. It fits within the range of the breeds studied, so I have no real reason to doubt it.

If anyone cares do to the reading, the abstract to the population structure study is here with a link to the full study: http://www.genetics.org/cgi/content/abstract/179/1/593

For those wanting to learn more about population genetics and effective population sizes:



I also like this page - if you scroll down you will find a section titled "Lessons from Populatin Genetics" and in it a paragraph explaining "Effective Breeding Population": http://documents.seppalasleddogs.com/html-documents/pbdb21c.htm

. . . And because this is not about complaining, I do believe this can be tackled, and should be by the best breeders which you most commonly do find involved in breed clubs. I have also known in my life others not involved in clubs and not even breeding pure (ie: the working Farm Collie, working Border Collie, and Alaskan Husky breeders I have known) who also do a bang up job, including health screenings appropriate for their breeds. I do have faith there are some of those kicking about as well especially in the working breeds.

I have much hope in Sarah Blott's program which includes consideration of retaining the genetic diversity we do have.

We all know there is plenty of room for examination and criticism of our current breeding system which I don't think should be addressed by defensivism, but should be welcomed for the insights it might give and solutions that may be offered.

Arlene and her three: J P - Alaskan Husky, Missie - Cavalier x Tibetan Spaniel, Rocky - All Sporty Cavalier:)

19th August 2008, 10:59 PM
Thanks for those additional links! :thmbsup:

20th August 2008, 11:23 PM
I find genetics an extremely fascinating subject. One of my friend's daughters has a PhD in human genetics so I love chatting with her.

I wonder, if it was made available & at an affordable cost, would the good breeders out there be prepared to have the dog's and bitches DNA samples tested and checked for compatibilty. You know, to check whether they are related in any way and also to see if they are carrying any disease that may result in unhealthy offspring.

I know it's available for humans so maybe in the not too distant future. I have a bad headache and have taken some morphine based pain killers for my back so correct me if I am rambling incoherently but aren't they now looking for a rogue gene that causes SM? Is this correct or am I dreaming?

I personally would want to see at least 5 generation pedigrees of both sire and dam of any pup I was considering buying, just to check for any inbreeding and also want to know how long the parents and grandparents lived to or how old they were - just as I did all those years ago when I was lucky enough to be blessed with Maxx.