Diversity FAQs
In over a fascinating year of participation in this list, with the fluctuation of listers there was and is an eternal reappearance of the same crucial questions by newcomers. While in the Canine Diversity Project a number of excellent articles explains the As and Os of genetic diversity, it is obvious that we need a FAQ list to be able to concentrate on the more detailed questions and spare discussion energy and time, giving clear-cut explanations to what most often is an open question or confuses critical newcomers. I think we, I mean those already fairly versed in diversity genetics, should cooperate to establish such a list.
So, hereunder several FAQs I believe are most frequently asked:
Q: What is the upper limit of the COI we should observe in breeding?
A.: There are not yet fixed or determinable limit as far, but basically problems or risk to emerge increase exponentially with rising COIs. Oftentimes, there seems to be a threshold but where? This is true for recessive defects and for inbreeding depression effects, especially fertility. Inbreeding damage depends on the severity of the genetic load, i.e. prevalence of defect alleles both for hereditary diseases and inbreeding depression. Dogs with low g.l. may remain healthy in spite of high inbreeding coefficients. With the current situation of dog breeding, all efforts should be made in every breed to halt and reverse the gene depletion process. Inbreeding can strike at every biological or physical function,sometimes at all.
Q.: Really, is not selection for health by far much more important than a low inbreeding coefficient (COI) or may thus even replace diversity breeding?
A. :The COI is just a probability that of a dog’s homozygosity level. (More accurately, it is the probability that two alleles of a dog’s gene locus originated in an ancestor by the division in two of a single allele – this is called identity by descent) Selection for health is indispensable, and so is boosting diversity. Health selection may promote beneficial gene combinations. In a progeny, there will be individuals with differing numbers of heterozygous genes in spite of the same COI (s. above). Selection for health may thus inadvertently choose the somewhat less homozygous dogs and/or those with heterozygous genes particularly important for viability. In this way, viability may be maintained longtime (but not for ever) in a line. As selection for working traits means also select the more viable, it also helps counteract inbreeding depression to a certain extent. Selection for health can always help the diversity effort but not replace it. These are two different pairs of shoes.
Q.: My breed is a rare breed, so where am I to go to outcross?
A.: There are methods to slow down the inevitable decline of diversity in small population of endangered species that could be applied to dog breeding. Another help would be DNA-Test on genetic distance (finding least genetic relateds among potential mating candidates ), or by computer pedigree analyses. All this often only delays homozygosity increase. Another way is crossing with a related breed. While there is great reluctance because of the still prevailing „pure race“ dog breeding system, this method was of necessity used repeatedly in various breeds. Already after four generations of back breeding, breed type can be nearly restored, so even when greyhounds were crossed with bulldogs, or Boxers with Pembroke Welsh Corgis!
Q.: My breed is very numerous. Do I still have to be concerned about finding a non-related sire?
A.: Even a very numerous breed can be genetically depauperate. Mostly there is just a handful of founders at the breed’s origin, and many decades of overusing few sires and inbreeding has disastrously accumulated the overall COI and spread defect alleles. This depends on the effective population Ne, a fictive, calculated number of dogs that determines the added COI per generation. This figure largely (it is a harmonic mean) depends on the smallest number of breeders in a breed’s history, i.e. first of all on the number founders and the propagating dogs during later genetic bottlenecks (in war times, periods of shrunken market interest, etc.) A great absolute number of breeding dogs, though much less affecting the Ne, diminishes the *additional* COI increase per generation and thus can stop further decline. Ne = t/(1/n1 + 1/n2…1/nt) where t= number of generations, nx = number of breeding dogs in each generation, thus if a breed starts with ten dogs and reaches 10.000in just 4 generations, we have ne = 4/(1/10 + 1/100 + 1/1000 + 1/10000) = 36! (from the German edition of Falconer, Introduction to quantitative Genetics). This shows, that even a numerically big breed can and mostly is genetically small, and that inbreeding coefficients will slowly accumulate in such a breed *even without the harmful popular sire effects or additional inbreeding!*
Q.: Should we breed carrier-free, if possible, or use carrier for carrier-non carrier matings? Some people say this is unethical!
By all means, no additional genetic genocide by carrier eradication! This would be just another severe blow for a breed’s already otherwise compromised gene pool! Only if the defect gene has also deleterious effects in the heterozygous combination, its eradication is to considered.
Q.: All right, but where are the hard facts from scientific studies on dogs?
There are figures from lab dog colonies that show fertility decline with increasing COI levels. Many vet studies show higher incidence of inherited defects in higher inbred dogs, more defects in inbred dogs is even an indication of the defect’s heritability, and then there is the comparison of health and longevity of the (totally outbred) mongrels and pedigree dogs (1 – 3 years longer average life expectancy of mongrels and better health in clinical studies). And last not least the striking provisional results of John Armstrong’s ongoing poodle study.
Q.: What changes should be made concerning breeding on the population level?
A.: Like rare species, breeds should enjoy science-assisted genetic management. Breed clubs should propose a well-studied choice of sires to the individual breeders, leaving if possible enough room for individual preference and selection. This may reek of authority interference, but if the dog buying public could be informed of a less risky buy and longer, less troublesome canine enjoyment this could promote the image of such a club and breeders would be willing to assume some restriction, being proud to belong to an organization of higher-than usual standard, an utopia? ) By the way, do have dogs not a right to be bred for being genetically intact, i.e. be provided with an adequate level of heterozygosity as a helpful means to warrant its chances throughout life?
So, that’s a few of those that itched me most. Hopefully they are agreed by the list’s knowledgeable people and experts. I feel a lot easier now. Perhaps some charitable fellow-lister puts it in a decent English? TIA!
I just wrote my FAQS when a message arrived I expected a longtime ago already: citing M. Willis with Lush quote. Unfortunately I “killed” that mail. Lush roughly said more opportunities for progress are lost by not inbreeding than by inbreeding, and Willis asked where do you go if your outbreeding program runs into trouble whereas if something is wrong in an inbreeding program where to you go for help?
Willis dates from ten years ago, Lush even from 1945, in a period nobody spoke or heard about genetic defects, not even CHD. Willis still could say at least in terminating his book: „This book has contained much about defects and it is important not to leave the reader with the impression that hereditary defects are legion in dogs. This is unlikely to be the case, at least in respect to serious defects.“ He mentions a study on a beagle colony and says: „The paper illustrates some of the damage that can result from one unwisely used animal but also emphasizes the low rate of the problem.“ (It was 2,16 % of defects in offspring of one particular sire versus 1,06% in dogs that did not descend from him), “I am quite confident that if we studied more populations and breeds we would find in most of them a relatively low rate of such anomalies. Let us hope that this book will keep it that way.“ ( p. 359 of Genetics of the Dog). But just ten years after, there are some breeds that are 30, 40 and 80 % affected by serious inherited diseases he mentions, and e.g. 70 breeds in Finland show CHD% of 35% on average. Times have changed… So the next FAQ would read:
Q: Based on Dr. Willis and J.L. Lush statements, can inbreeding be really all that bad on the population level?
A.: Inbreeding strongly increases risk of defects and loss of all kinds of viability traits. It is less harmful on the population level, as the many alleles lost in one inbreeding kennel are probably mostly others than in another, so on the population level there results a certain balance. Irresistibly, our dog get more and more dependent on veterinary medicine in all ways of life, a fact to attribute to genetic deterioration and allele losses. Yet, some alleles may still get irretrievably lost, and they may be important ones. We don’t know enough on this subject yet. So if you inbreed, you go act against your own dogs health and wellbeing, while the successful popular sire owner can jeopardize a breed’s or part of a breed’s future. As to the „progress“, are today’s dogs any better or more beautiful than yesterday’s? I see more change in type fashion than in actual soundness, let alone health, and IMHO the present dogs are no better performers than their ancestors, rather conversely (perhaps with exceptions to the rule).. Policemen, Hunters and others, many lament declines in the usefulness of their present dogs as compared to former days.
Q.: But I just need to outcross if there is inbreeding trouble?
A.: Chances are you may not find any outcrossable sire any more, when the whole breed is already related at 20 – 30 % COI, as most are. In an older American book on the GSD (!) the author already deplored the difficulty finding an outcross chance in that breed….
Q.: Outcrossed dogs lose type, isn’t it?
A.:If properly assortedly mated, the risk may be there but slight. Even Willis acknowledges that. On the other hand, inbred litters may also become heterogeneous, because of developmental instabilty by inbreeding. A successful boxer breeder told me, best result she gets with intermediate COIs in the breeders’ groups. In the interest of the dogs’ genetic welfare I would hope breeders groups would disappear in future, or uniformity requirements eased.
(by breeders groups He means- “A number of self-bred dogs exhibited and judged as a group.”) >We call it (in USA) the Bred-by -exhibitor class.)
Q.: Why then old-time writer are so fond of inbreeding?
In order to create a breed from a very heterogenous landrace or from breed crossing, inbreeding is a very helpful means indeed. So helpful, that our breeds today would rather need a little more individuality (but of course in the frame of a general well defined breed type). Variatio delectat (G)
Q.: What is the difference between linebreeding and inbreeding?
A.: Many a dog would be happy had it as much diversity in it as I have read definitions on these terms. Scientifically, inbreeding is every breeding act that produces progeny with a higher COI than the average of the breeding population. Breeding sibs, halfsibs and parents-children is incest breeding. Linebreeding is mating less related dogs. In order to make sense for a notable gene-accumulating effect, dogs are bred to a not too remote ancestor, e.g. mating cousins gives a 6,25% higher COI in the progeny. (if we define linebreeding as breeding to a common ancestor, all breeding of dogs is linebreeding because at least some tenthousands years ago all have some common ancestor(s). Line breeding is „mild inbreeding“ as homozygosity increase is slow compared with incest breeding (25%)
Q.: (plagiarized from Frederic „Doc“ Cornell : „What generations of dogs likely known to the general dog fancy (not just a single and isolated dog), that have been a product of the diversity breeding theory *exclusively* (in contrast with dogs of linebred or inbred pedigrees), have achieved documented acclaim with regards to performance, health, and longevity?“
A.: Mongrels are the only one example existing ASFAIK, they *on average* excel at least in longevity and health, and they fully comply to all of „Doc’s“ prerogatives. An vast comparative „study“ on the difference of genetic diversity versus depletion. Not to forget John Armstrong’s poodle inquiry.
References:
G.J. Patronek, D.J. Walters, L.T. Glickman, Comparative Longevity of Pet Dogs and Humans: Implications for Gerontology Research, J. Geront.,
BIOLOGICAL SCIENCES, 1997, Vol 52A,No.3, B171-B178
B.N. Bonnett, A. Eigenvall, P. Olson, Å. Hedhammar, Mortality in Swedish dogs: rates and causes of death in various breeds, The Veterinary Record, 12/7/1997, S. 40 – 44)
Renner, A. S., Statistische Analyse der Rassenverteilung, Erkrankungsfälle und prophylaktischen Maßnahmen bei den häufigsten Hunderassen am Beispiel der Patientenpopulation einer Kleintierklinik in Südbaden von September 1987
– Juni 1992, Diss., Inst. F. Pathol.,Tierärztl. Hochschule Hannover, Hannover,1995
Dr. Hellmuth Wachtel
Free collaborator of the Austrian Kennel Club
Member of the Scientific Council of the
Vienna Schoenbrunn Zoo
More Information about genetic health for dogs from Dr. Wachtel