Μολοσσός της Ηπείρου

written for Dog World, Jan 6th 2009 by DR. BRUCE M CATTANACH

http://www.steynmere.com/INBREEDING.html

Dr. Bruce Cattanach:

B.Sc (Hons) in Agriculture, 1955;

Ph.D in Mutagenesis and Mammalian Genetics, 1959;

D.Sc in Mutagenesis and Mammalian Genetics, 1972;

Elected Fellow of the Royal Society, 1985.

Scientist Medical Research Council Mutagenesis Unit, Edinburgh,1959-62 and 1964-66;

National Institute of Health Post-doctoral Fellow, Oak Ridge , Tennessee, 1962-64;

Senior Scientist City of Hope Medical Center, Duarte, California, 1966-69;

Senior Scientist Medical Research Council Radiobiology Unit, Harwell, Oxford, 1969-85;

Head of Genetics Division, 1985-97;

Director of the newly created Mammalian Genetics Unit 1997-2000.

Author of over 250 published papers. Specialist subjects; chemical and radiation mutagenesis in mice, analysis of mutations, control of X-chromosome inactivation, sex determination, genomic imprinting.

 Way back in my agricultural college days, animal breeding lectures started with the pioneering work of Robert Bakewell in the 18th century, the farm enclosure system, and the founding of breeds. Bakewell’s work showed the advantages offered by inbreeding for establishing breed type. His results were eagerly taken up by the early dog breeders and by kennel clubs around the beginning of the 20th century and have been promoted in dog breeding books ever since. The dog breeding world recognised that inbreeding could lead to the appearance of unwanted recessive gene effects, but so much other substantial genetic work conducted in diverse animal and plant species showing that inbreeding has other ill effects has been largely ignored. I refer to the loss of  fitness, reduced fertility and general failure to thrive.

The BBC film, Pedigree Dogs Exposed, has brought the whole question of pedigree dog breeding into the limelight. The programme  focussed largely upon the high incidence of genetic abnormalities and other deficiencies seen in many breeds and presented inbreeding as the cause. Is it?

I would like to consider this question from three angles:

1. It seems fixed into the minds of human geneticists that every one of us harbours about 7 deleterious recessive genes. Hence the scientific basis for the taboos on inbreeding in humans. But the concept is now applied to dogs and claimed as a reason why inbreeding should be avoided. But were deleterious recessives to be so common in dogs, every one of us who breeds dogs would be finding abnormal pups in most litters, and this is patently not the case. Explanations offered for this have included the reductions in dog population numbers during World Wars, the small size of founding populations, and maybe even the tough association canines have had with man over historical times. All may have done much to weed out deleterious genes that were originally present!
2. However, every dog breeder knows that inbreeding brings recessive genes to light. Well, is this such a bad thing? At one level, I don’t think so. Without inbreeding, the fate of a gene in a breed is up to chance. Undetected, it can become widely distributed and prevalent such that effectively, the whole breed becomes involved. Detection occurs only when carriers, by chance, are mated together, but by this time there is little that one can do to resolve the problem. On the other hand, if there has been any inbreeding and an unwanted recessive gene is detected before it becomes widely spread, something can be done. In these circumstances inbreeding can provide a useful service; it warns if a problem is present in a breed and, by identifying carriers, it provides a solution. The real damage only occurs when nothing is done.
3. However, there is also the phenomenon of inbreeding depression. Again, everybody has heard about this but few breeders would claim to have experienced it. Even just a few weeks ago, this paper stated that there is no evidence for inbreeding depression in dogs. But this is not true. There is much compelling literature on the subject. For example, check http://www.geocities.com/willowind_dals/ - and there are also many published scientific papers on the subject. The difficulty is that to recognise inbreeding depression one has to measure the fitness criteria (fertility, viability etc) but few of us have the numbers of dogs to do this. However, when one finds declining litter sizes, difficulties in rearing pups, high incidences of cryptorchidism, or dogs which lack interest in mating and other such general difficulties, then one may be standing at the edge of a slippery slope. I am afraid that many breeds will die out in the next few years as the inbreeding levels keep rising - and they must if note is not taken of what we are doing and remedial action taken. And it is the policy of constant inbreeding, including line-breeding, that is the root cause.

But, what about the big question? Is there even a need for inbreeding/linebreeding these days? Following the setting up of KC registries and the development of breeds at the start of the 20th century, there would have been heavy inbreeding. This would have helped create and fix the various types into breeds. But we now have the breeds. They are fixed. We should be competing to breed the dog closest to the standard but not by inbreeding as this creates only a series of sub-breeds. We should be looking at the whole population and, as in nature, selecting the best at all levels without insistence upon inbreeding. The buzz term these days for this very old established form of breeding is assortative mating, the breeding together of animals as unrelated as possible but as alike as possible and conforming to the desired type.

So, is this just fancy theory or is there any evidence to support its efficacy? There is the clear evidence that present-day farm animal breeding makes every effort to avoid inbreeding. I don’t think anyone has actually written about it in dog books but the evidence exists if one looks. Back in 1979 I wrote a little article for a Boxer magazine entitled “How to breed a champion: What the records say”. It presented a rough analysis of the champions bred over the previous 15 years, asked whether they derived from inbreeding or outbreeding, and whether their parents were champion class or not. In addition it asked whether it made a difference to the success of stud dogs whether they were inbred or not, and whether they were champion class or not. One can pick holes in arguments offered but the conclusions are still clear. Despite the frenetic inbreeding philosophy of the time - the perceived essential need to tie in- more than half the champions bred derived from outcrosses, and particularly in the highly inbred groups it was very important that the parents were of champion class. As to the stud dogs, it mattered little whether they were inbred or not, but the best producers had the best parentage. The article can be found on my website: (www.steynmere.com)

In case these old results were a fluke of the time, I updated the records about 8 years ago for a Boxer Club teach-in, and I obtained the same results. The exercise has since been performed in two others breeds with, again, the same basic findings. And a few weeks ago Simon Parsons summarised his survey of the pedigrees of recent group winners and I think he found that all types of breeding produced top winners - perhaps the same result again. I would be very surprised if this is not the general situation but do check for yourselves.

In conclusion, I suggest that there is no need to inbreed/linebreed these days and the price we will pay for continuing to do so, whether as standard procedure or otherwise, will be far too high.