Two Cavalier King Charles Spaniels mating. To read about the creation and wreckage of this breed, click here.
A new study from Imperial College, London has come out supporting the thesis that Kennel Club dogs have been wrecked by 19th Century genetic theories and show practices which remain the foundation stone of The Kennel Club's closed registration system.
This is bad news for The Kennel Club as the Imperial College study (published in the journal Genetics) echoes the conclusions of a one-hour special entitled Pedigree Dogs Exposed to be shown August 19, 2008 and also on the BBC web site.
Even more damning, the Imperial College study uses The Kennel Club's own data to show how inbred modern purebred dogs have become.
The study, entitled Population Structure and Inbreeding from Pedigree Analysis of Purebred Dogs (PDF) was co-authored by two researchers from the Imperial College's Department of Epidemiology and Public Health, an expert from the Waltham Centre for Pet Nutrition, and Jeff Sampson of The Kennel Club, who supplied the underlying pedigree data used by the researchers. The research itself was funded by the U.K. Biotechnology and Biological Sciences Research Council.
For folks interested in learning more about the historical background leading up to current levels of inbreeding (i.e. "How did we get into this mess?") read Inbred Thinking -- a concise history of the historical and intellectual development of the Kennel Club and its closed registry system. A printed version of this article appeared in K-9 Magazine in May of this year under the title of "Will a Closed Registry Lead to Genetic Genocide for Certain Dog Breeds?"
Back to the Imperial College study: What does it say, what data is it looking at, and what are its conclusions?
Some summary points:
- The study is based on a 10-breed sample of 2.1 million dogs in the Kennel Club's electronic pedigree data base. The Kennel Club's database contained records of a total of 5.7 million dogs from 207 breeds as of the end of 2006. The Kennel Club's electronic data base was begun in 1970.
- This is the first systematic attempt to study Kennel Club population structure using The Kennel Club's own pedigree database.
- The 10 breeds examined were: the Rough Collie, the Golden Retriever, the Boxer, the English Bulldog, the Chow Chow, the Greyhound, the German Shepherd Dog, the Labrador Retriever, the English Springer Spaniel, and the Akita Inu.
- The researchers note that inbreeding condenses and exacerbates genetic disorders with a population:
"Dog breeds are required to conform to a breed standard, the pursuit of which often involves intensive inbreeding .... This has adverse consequences in terms of loss of genetic variability and high prevalence of recessive genetic disorders. These features make purebred dogs attractive for the study of genetic disorders, but raise concerns about canine welfare."
- The researchers note that many dog breeds are associated with specific genetic disorders that have been magnified by inbreeding:
"Many diseases affecting dogs have high prevalence in one or a few breeds, such as Addison’s disease, common in Portuguese Water Dogs (Chase et al., 2006), interstitial lung disease in West Highland White terriers (Norris et al., 2005), and dermoid sinus in Ridgeback dogs (Salmon Hillbertz et al., 2007)."
- The authors found disturbingly high levels of inbreeding within most Kennel Club breeds they looked at:
"We find extremely inbred dogs in each breed except the Greyhound, and estimate an inbreeding effective population size between 40 and 80 for all but two breeds. For all but three breeds, more than 90% of unique genetic variants are lost over six generations, indicating a dramatic effect of reeding patterns on genetic diversity."
Or, as the press folks at Imperial College put in in layman's terms: "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 number of generations studied ranged by breed from 5.9 in Greyhounds to 9.0 in the German Shepherds, with an average over the ten breeds of 8.0 generations of dogs analyzed.
- Popular sires are part of the problem, but not all of the problem.
"Popular sires (defined here as > 100 recorded offspring) are evident in all breeds except Greyhound. Golden Retrievers have the largest proportion of popular sires (10%), and conversely the lowest proportion (5%) of male dogs that are sires. . . . Highly-prolific dams (> 40 offspring) are concentrated in three breeds: German Shepherd, Golden Retriever and Labrador Retriever. Most dams have just one litter recorded."
- A closed registry system is the core of the problem.
"Dog registration rules have only been rigidly enforced for about 50 years, prior to that occasional outcrossing was still possible."
- The Kennel Club needs to change the way it does business.
"We have found that the loss of genetic diversity is very high, with many breeds losing over 90% of singleton variants in just six generations. On the basis of these results, we concur with Leroy et al. (2006) that remedial action to maintain or increase genetic diversity should now be a high priority in the interests of the health of purebred dogs. Possible remedial action includes limits on the use of popular sires, encouragement of matings across national and continental boundaries, and even the relaxation of breed rules to permit controlled outcrossing."