Popular Sire syndrome and concerns of genetic diversity
By Cesare Giammiro (Bear-Pak Malamutes)
There are sure very different ideas regarding breeding plans and methods, especially regarding tight breedings as opposed to plans based on low inbreeding coefficients.
In Europe (and especially in northern countries from what I know) the tendency is to breed with low COI's, the reason being the concern regarding health that is somehow supposed to be at risk with tighter breedings.
Altough this may be true to an extent I think this has probably more to do with problems related to certain lines and specimens than to the way they are bred.
Breeding two unhealthy dogs will only produce more of the same, and therefore, if a problem is hidden linebreeding will make it evident.
But this has nothing to do with linebreeding in itself; we may say that linebreeding may bring to the surface pre-existing problems rather than creating new ones.
It is a matter of trying to understand wether one prefers not to run the risk to incurr in a problem or if one prefers to know what problems are hidden behind an apparent healthy line and trying to solve them if and when unfortunately they may show up.
One thing is for sure, a healthy linebred dog offers much better guarantees to be from genetical defects than one coming from generations of outcrosses, and this is particularly true about simple recessive traits.
It is not my intention to convince anyone to change theyr mind or even less to judge anybody or any breeding plan of course, but while I must admit that some breeders are obtaining good results with plans based on low inbreeding coefficients, I also wish to make it clear that the tight breeding approach to purebred breeding still makes a lot of sense, at least so long as it is backed up by a good knowledge of the potential risks and defects that a given line may carry.
Despite this facts, the latest "fashion" and the most fierce (and less moderate) opponents of linebreeding/inbreeding are considering this as a disreputable practice that serious breeders should not even contemplate, if not for other reasons for the safeguard of the "genetic diversity" of the breed.
While it is not the goal of this article to discuss the issues related to etherozigosys, homozygosis etc.. (and the risks of extreme positions that in some cases are threatening to ban the breeding of purebred dogs...), I think it is important to bring to the attention of dog breeders the results of a recent study that explains how and why linebreeding is probably the best way to preserve the "genetic diversity" that we all care for and that of course is so important for the future of the breed.
The results of this study was summarized in a presentation that was feautured in the February issue of the 2004 AKC Gazette page 73, by Lynne Kuczynski Veasie, about the 2003 Canine Health Conference , entitled "Popular Sire Syndrome and concerns of genetic diversity" (see below):
2003 AKC canine health conference
Popular Sire syndrome and concerns of genetic diversity.
"Breeders underestimate the amount of diversity that can be present in a breed, even one with a limited group of founders.
A molecular genetic study of the Chinook dog, which was reduced to four individuals in the 1970s, showed there was significant gene diversity and heterozygosity in the breed.
The perceived problem of a limited gene pool has caused some breeders to discourage linebreeding and to promote outbreeding in an attempt to protect genetic diversity. However, this is based on a fallacy.
Studies in genetic conservation and rare breeds have shown that this practice actually contributes to the loss of genetic diversity: by uniformly crossing all "lines," or families of dogs in a breed, you eliminate the differences between them, and therefore lessen the diversity between individuals.
The process of maintaining seperate lines, with many breeders crossing between lines and breeding back as they see fit, maintains diversity in the gene pool."
written by Lynne Kuczynski Veasie, guest columnist of Skye Terrier Feb
Column in AKC Gazette 2004. P. 7
What some breeders don't seem to realize is that despite the relatively small number of foundation dogs upon which our breed was based, we are used to working with lower COI's than most other breeds, and personally I don't see why we should worry and try to make them even lower.
So I think that basically it is not a matter of "breeding wide" to avoid problems; it is first of all a matter of preventing affected dogs or carriers from being bred, and second it is a matter of preventing the same genes to be widespread over a large population, which happens basically when all are breeding from the same stud (popular sire syndrome), and because of mindless outcrossing.
This is a situation that we should know quite well in Europe, and this is proved by the fact that it is very difficult to find here pedigrees that don't contain the same lines which I won't mention but that we all know to be very popular in our continent.
I think this is the true enemy of the future of the breed.
As to the reputability of breeders according to theyr breeding plan, I do not think this is inversely proportional to COI's as some suggest; the lower the COI the more reputable the breeder.....
To me the reputable breeder is the one:
- who always screens breeding prospects for hereditary diseases. And about this point let's all remember that so called "doubles" are the safest screening method for simple recessive defects;
- who works within his/her own line with occasional outcrosses;
- who doesn't run after the top winning stud of the moment, unless genetically compliant to his/her line and carries no hereditary defects.
- who doesn't "pollute" a large part of the population with his/her own gene pool. This is achieved not only thru production of a few litters, but also thru refusal of stud service to unsuitable and unrelated lines.
Maybe my thoughts are emphasized by the difficulty which I encounter in working with a line (T'domar Kodara) which is not well represented in Europe, but I think the biggest problem will come the day we all will have no more lines to outcross to, and this is one of the reasons why I think we all should try to work on our gene pool in order to create well defined "blood lines", so that it is still possible to "outcross" to other linebred specimens of similar "blood stream" (going back to same ancestors and of same type) favouring "hybryd vigour" and genetic recombination while maintaining a genotypical diversity with other lines and lowering at the same time the risk to "import" undesired phenoltypical traits.
After saying all this, I must say that of course I agree that breeding too tight for several generations may cause problems, although this probably depends a lot on the lines involved in the program and on experience and knowledge of the breeder, as some lines that were linebreed with high COI's (10% to 20%) for many generations are not showing yet any sign of genetic depression.