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Does greater inbreeding always mean poorer health?

According to the Pedigree Dogs Exposed Blog... it doesn't - and I tend to agree!!


A lot of work has been done recently on recording in the breed database, the COIs of the entire UK-bred IRWS of 30 yearsl - over 10 generations together with some Irish-bred and other overseas-bred IRWS too. So there is a wealth of information to work with.

As the database is arranged chronologically, litter by litter - with the litter COI and those of its parents, together with health test results of all, it can be seen that the COI bears little relation to the hereditary conditions we have already dealt with and to isolated health problems.

As far as can be seen the distribution of COIs has been constant over the 3 decades with the vast majority being in the 11% - 29% region - too high, for sure and breeders are advised to select mates to bring the inbreeding % down. Howeverone judicious mating can bring even a high COI down to single figures but at what cost to the breed's specific qualities - temperament, type and performance - and health? 

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Ann, Mel,

I hesitate to put my thoughts in words and am very aware that my views may not be shared by the majority on this list. Still I dare...

It seems the great fear of outcrossing stems from the risk of introducing new problems into the lines we believe we know. I am a breeder with an interest in genetics but I would not go as far as to say I understand in full the complexity of this science. I have however come to believe that in general the risk of not outcrossing far outweighs the risks of introducing new 'blood' into a line. Why is that so? Many inherited diseases follow the mendelian rules of recessive / dominant. Not all, obviously. When a breeder chooses to outcross he/she will rely on all the information he/she can get on the health/temperament/performance issues in his/her own line and in the line intended for the outcross. If a presumed inherited disease is visually present (ie phenotype & genotype 'affected') in the animal we are considering then obviously the animal will be discarded. If a problem is not visible the animal may be carrying a recessive gene for a disease. BUT, due to the fact we are not replicating the gene by linebreeding it is highly unlikely that the recessive gene for a certain disease will meet on the same allele coming down from the other line.

Diseases that are termed gentically 'dominant' ie only one allele is required for the dog to be affected, will be visible and can hereby be avoided.

This means we can actually outcross for one generation and profit from the so-called heterosis effect and then go back to the lines we prefer. The risk only comes if we then happen to decide to inbreed / linebreed back to those same animals we started off with.

The risk of continuing linebreeding in a population that has been linebred for a century is higher than that of introducing inherited disease through an outcross. Geneticists with wider experience of breeding practice than most dog breeders (as they normally deal in farm and laboratory animals for a living) have outlined the fact that an outcross will have a positive influence on vitality parameters (see also the MHC article).

Obviously the difficulty such breeders are confronted with is getting access to all the information on health issues that is needed. The IRWS breed has been recording health problems in their breed over the past 30 years. AFAIK this information is not made available to the public. As Mel says, only experienced 'insider' breeders know of some problems in lines (ie less experienced breeders 'are asking for trouble'). That is sad because problems - be it health or other - really ought be out in the open. Problem issues can only be managed if such knowledge were made public without resorting to finger pointing and accusations.

A public database and a breeding concept that moves away from the individual breeder laying the highest value on 'one's own line' to looking at the whole breed population might be a way forward. 

But to be quite honest I don't think that will happen. 

Very well written as usual Susan.....and so clear and concise

I agree with you.


This what I would have tried to write if I could....but you have said it better than me.

Also, I have noticed in other Forums how it is mentioned that in the humans, line breeding does not happen and yet there are health problems......but I would like to ask....have you looked into what happen when line-breeding does occur in humans. This does occur in populations which are still cut off from the rest of us ( for example on living on islands or in remote mountain or jungle areas. Closer to home, has anybody seen or remember the film 'Deliverance'? This illustrates what tends to happen in line bred humans. I hope I have not offended anybody by comparing dog populations with humans populations? :-))

Catherine...others on this site have already compared human breeding to dogs and no comments were made in return so I can't see why any should be made now...although I wouldn't hold my breath if I was you!!

Your question was "have you looked at what happens when linebreeding does occur in humans?".

My answer is yes.... and it not good!

I would call the human form 'inbreeding' rather than 'linebreeding' though :-))

I agree.  If you would like to take a parallel with humans and dogs then certainly if you look at Royal families who have interbred you can see genetic disorders, lowered immunity, susceptibility to allergies etc and, yes, you do see this also in close communities.  I recently read an article in The Times by Tamzin Alayah-Brown about health problems in the UK Muslim community resulting from inter-marriage between cousins.  But I will also re-iterate that humans can produce genetic disorders from total out crosses.  The same can happen in dogs.

The difference between producing humans and breeding dogs is that humans procreate without conducting any previous research and don't seen too bothered about the outcome.  Whereas we in dogs agonise, pour over pedigrees, conduct research.  You have only to read the immense amount of material about this subject alone on ES to see how much importance we set by it.

I very much agree with Susan that we can most certainly benefit from outcrossing and then breed back into the lines we prefer.  If we are sensible, in theory, we should be able to maintain type and conformation without compromising health.  The problem is that sometimes life deals us a bad hand and despite all our careful planning sh.. happens.

I do sincerely believe that breeders are now more revealing about the problems they have had in their lines and more willing to discuss and exchange information, certainly among my close friends both here and overseas.  I do think this is happening Susan. 

Thank you Catherine, Val and Eva for your positive comments.

Inbreeding in humans... certainly! The inhabitants of Iceland I believe are well versed in population genetics. And here in Switzerland (mountains with what used to be secluded valleys) the inherited eye condition of Retinitis Pigmentosa (RP) is well known. This is very similar to PRA in dogs (I think it was mentioned in one of the other blogs) and leads to blindness in humans. It is caused by a simple recessive gene. In the Swiss valley of the Wallis this was the main cause of blindness (for people). Even today there are Swiss families with three generations affected by Retinitis Pigmentosa. This came about due to the isolation within the valley and the habit of cousin marrying cousin. So very similar to the royal families Eva mentions. Again the Habsburgs come to mind.

There is no one simple solution just as there is no purely black or white in any aspect of life - certainly not when breeding dogs...

Outcrossing will not guarantee the absence of genetic disease. There will always be instances of the best plans going wrong. But these instances should not be used as proof that the whole idea of outcrossing is wrong until it has been tried...

Outcrosses to animals of the same breed (but with no common ancestors over 10 generations) and more so outcrosses to a different breed should lead to an increase of healthy animals.

Quite recently the new Swiss breed cub for the 'Continental Bulldog' has applied for recognition by the FCI. This was a Swiss effort to create a breed similar to the old type of bulldog found at the beginning of the last century in the UK. These dogs have longer muzzles and longer legs than their cousins the English Bulldog and have no trouble breeding. They do not suffer the same health problems that the English Bulldog is known for.

Not the elegance of a Setter, I know...;-)) but interesting all the same. 

Hi Mel,

sorry to bring this so close to home. I would assume that similar to PRA in dogs there are different types of RP in humans and different modes of inheritance also?

Dee, Mel,

Same in people as in dogs: when two carriers meet up even from unrelated parents - if the gene is the same the outcome will be 'affected'. Still, the chance of that happening is a lot higher in an inbred population than in an outbred one.

There is no living being with only 'good' genes and try as we will: with linebreeding it will never be possible to preserve only the good.

That program did throw up some good points but taken out of context then anything can be made to look bad...and most of that was taken out of context, but the KC didn't come out whiter than white...

But as for line breeding and high COI, if done properly it is a very useful tool in animal breeding...But because you are concentrating genes so highly then with those good traits...you are also doubling up with the bad ones..this is definitely a case for knowledge...without that then your line breeding simply becomes inbreeding...and that isn't the way to go...it again is being honest, and not all of us are...(not throwing any stones at anyone in particular wouldn't want to do that all) 


I actually think a database with an open register of all health records would have been very much praised by the makers of Pedigree Dogs Exposed. I may be wrong... but I feel that is the kind of thing that the general public and the newcomer breeder (and the established breeder too!) would appreciate.

Yes, I agree it is definitely good news that breeders are discussing issues more openly. I hope it will become more common practice, with newcomers continuing like-minded. But the established breeders will need to leed the way. 

I'm not sure it is a matter of the newcomer not being willing to study - in my experience the willingness is there but just not the realization of how many 'problems' they need to be aware of. Take bloat for example. It is often not realized by 'old' and 'new' breeders that bloat can also have a genetic background. Before you are able to ask questions you first need to be aware there are  questions to be asked... Unfortunately most of us have made the wrong choice some time or other - why is that? Did we not ask the right people the right questions or did we just not realise we should be querying any particular point?


On an aside, you must have Swiss relatives...;-)





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