Thursday, 1 September 2011

Does greater inbreeding always mean poorer health?

I spend a lot of time writing about the perils of inbreeding so it's interesting to find a report - albeit a preliminary one - that found that inbreeding did not lead to poorer health.

"One problem in modern dogs is a high occurrence of physical diseases, defects, and disorders. Many breeds exhibit physical problems that affect individuals already at young ages, and veterinary care and/or various drugs are in some cases needed throughout life," report the authors of the report in the Veterinary Journal of Behaviour . "A potential cause of these problems is inbreeding and loss of genetic variation that is known to reduce the viability of individuals and is associated with increased occurrences of hereditary disorders governed by autosomal recessive alleles. During recent years increasing conservation genetic focus has been devoted to domestic animal populations. This attention includes both scientific efforts and international and national policy work. Domestic populations are traditionally bred through strong selection. Only a few animals are used in breeding, resulting in considerable loss of genetic variation. Conservation breeding aims at reducing the rate of loss of genetic variation, and this includes reducing selective pressures. This research addresses the question of whether “unhealthy” dog breeds exhibit elevated rates of inbreeding and loss of genetic variation as compared to “healthy” breeds."
The researchers used pedigree records from the Swedish Kennel Club database and classified the 14 breeds they looked at as "healthy" or "unhealthy" based on data from four Swedish pet insurance companies.

The “unhealthy” breeds were Bull Mastiff, Dogo Argentino, Bulldog, Mastiff, Neapolitan Mastiff, Irish Wolfhound and Shar Pei,. The “healthy” breeds were Finnish Lapphund, Norrbottenspitz, Norwegian buhund, Norwegian elkhound black, Småland hound and Coton de Tuléar.

The preliminary results did not find any difference between healthy and unhealthy breeds with respect to the average level of inbreeding among living animals. However, there were indications that the rate of loss of genetic variation was slightly higher among unhealthy breeds.

The authors stress that the results are preliminary. The pedigree data only went back to the start of the Swedish KC electronic database (around 1970) so may not be a true indicator of the breeds' level of inbreeding. The researchers also only looked at small-population breeds. But the findings are interesting nevertheless and serve to illustrate that inbreeding may not always result in a less-fit population.

"The plan is to also include breeds with larger population sizes and we hope to publish something more this winter," says co-author Mija Jansson, a population geneticist from the Institute of Zoology at Stockholm University.


  1. Fascinating! Nothing is ever black and white is it?
    Vicky P

  2. What strikes me about these two lists is that one of them is composed of dogs with very exaggerated physical traits, and one is composed of dogs with pretty moderate conformation, lack of extremes.

    Is this evidence that selection for physical extremes is more harmful than homozygosity?

    As for the issue of whether or not pedigree records reflect the actual level of inbreeding, can't studies of MHC homozygosity answer that? Obviously more expensive and intrusive than just pedigree analysis, but a logical next step.

  3. It's probably a combination of both physical structure extremes and homozygosity. Obviously breeds like the bulldog are going to have a lot of problems that aren't genetic but are as a result of selection of structure- short nose, protruding eyes, hip problems due to body structure.

    Less extreme breeds can have a lot of issues too, though- Labrador retrievers, poodles etc that can't be attributed to extreme features.

    Dogo Argentinos aren't exaggerated, are they?


  4. This study does not strike me as particularly comparing like with like. Kinda dents my confidence in the results. What Heather said, basically.

  5. The results of the research dont surprise me. Some breeds are just healthier than other breeds. Partly its a matter of luck and chance with how many "bad" genes the founder dogs in the breed carried. Some of the health problems, as Caty said,are more to do with extreme construction
    Some of it due to the number of generations of inbreeding until you get back to the founder dogs eg the wolfhound has far more generations of "pure" breeding" than the Finnish Lapphund.
    I think one would find more correlation between inbreeding and health problems by comparing dogs in a single breed, rather than by comparing breeds. And even within a single breed, one will find some dogs with high COIs who have surprisingly few problems, and some dogs with lower COIs who have health problems. But on average , within a breed, the number of health problems will be worse with higher COIs

  6. Could selective sweep for fixed traits such as brachycephalia (for example) increase the levels of homozygosity in the "unhealthy" breeds?

  7. Great blog. Nice to see more on population genetics. Another interesting article that covers some of the dynamics of population genetic diversity in purebred is here.....

  8. Several of the breeds listed have an open studbook (ie. Norrbottenspitz).

    Something that isn't mentioned. That alone would have a huge effect on the health of the dogs.

  9. No expert on genetics, but this strikes me:
    1) you must first sort out breeds which are structurally unhealthy, i e have been bred for features which are direct results of deleterious genes. Cranial dysplasia, referred to as "brachy", for instance. If such a breed was as genetically diverse in all other gene pairs as nature will allow, the dogs would still have breathing problems and so be "unhealthy".
    2)If you look at certain other breeds, which were made into formalized breeds comparatively recently, AND before that had a long history of selection for usefulness under harsh conditions - let´s imagine a Lapponian reindeer herder and general purpose hunter, fed on scraps, expected to run for hours beside the sledges in freezing temperatures, all sickly puppies culled quickly and any sickly adult too because no demand for dogs that couldn´t contribute.
    Now, if you decided to start a formal breed from a fairly small group of individuals picked randomly from such a population of dogs, and if you had not had such a very large number of dog generations because the breed was a relatively new one - would it be a surprise that as yet you had healthy individuals?
    Particularly if there was, or had been until recently, an open studbook to help...
    Will look out, though, for more news from this study project.

  10. Thank you, all, for showing interest in my work!

    @Heather - I am not a vet-student so I have not looked at physical extremes even though it would be very interesting, of course. Pedigree analyzis and molecular studies answer different questions, what I'm first of all interested in are the increase in inbreeding over time.

    @Dave - Have you found any proofs of correlation between open studbook and health of the dogs? I have only used data from the Swedish kennel club and they do NOT have an open studbook for Norrbottenspitz as the Finnish kennel club has.

    There is no scientific definition of open studbook so it is a bit hard to discuss but if it is defined like in Sweden (cross breeding between breeds occur) there is only one of "my" breeds that have an open studbook in Sweden - Småland hound.

    The Småland hound is in a so called "rasvård" project. ("Rasvård" may include genetic health programs for both physical and mental health and overall health and breeding programs at the population level. Combinations of these actions may occur in individual breeds.)

    /Mija Jansson

  11. Is it possible that there has been imports from Finland to Sweden of the recently registered Norrbottenspitzes? So the open studbook in Finland would have had an impact on the breed in Sweden also.

    Open studbook in Finland (Finnish KC) means that there are national (Finnish) rules that facilitate registering dogs outside the studbook to Finnish KC special registry. These are in addition to the FCI rule about the right to apply registration of unregistered dog. Breed that have such rules in Finland i.e are considered to have an open studbook include (but are not necessarily limited to) the aforementioned Norrbottenspitz, Lapponian Herder and Jack Russell Terrier (this JRT mean the FCI breed number 345).

  12. @Mija Jansson

    So, in the papers, there's no RKF or FKC in the pedigrees? It's all SKK straight from the foundation?

  13. Submitted too soon.

    No, I am not suggesting a correlation between open registry and health of the dog. I am just pointing out the limitations of the study. Unless one maps the entire pedigree straight from the foundation, one cannot exactly say it is a closed registry. Even importing from another kennel 15 generations ago would make all the difference despite the current COI.

  14. Not surprising. Breeders have known for decades that rigid selective breeding can eliminate/avoid health problems. I believe you negatively refer to that as eugenics, LOL.