Conservation Breeding Principlesby Jeffrey Bragg
“…if you are concerned about inbreeding, genetic diversity, and inherited illnesses, you might wish to consider implementing some of the following principles whose observance we have found useful in the Seppala Siberian Sleddog Project.
BALANCE OF SIRES AND DAMS
Make a great effort to maintain a reasonably equal numerical balance of sires and dams; don’t consistently use fewer individual sires than dams. The so-called “popular sires” syndrome has received much discussion and attention. What may not be as well realised is that this selfsame syndrome is repeated in miniature in most kennels, where one or two of the “best” males cover all the bitches, sire all the litters. (How often has one heard it said that “the best males should sire all the litters!”) In order to avoid needless reduction of the effective breeding population, just as many individual males as bitches should contribute to the population; this holds true whether we speak of the breed population as a whole, or of the population within a single kennel.
Do no incest breeding whatsoever (even if you would rather call it “linebreeding” or inbreeding). Matings of related individuals closer than cousins ought not to be contemplated unless it should become absolutely necessary to prevent loss of a bloodline. This means: (a) no brother/sister matings, (b) no father/daughter or mother/son matings, (c) no half-brother/half-sister matings (i.e., sire and dam share one parent in common), (d) no grandsire/granddaughter or grandson/granddam matings. This does not mean that first-cousin matings (sire and dam have different parents but the same grandparents) are okay or recommended; it is simply a case of having to draw a line somewhere, at a given degree of consanguinity, in order to say “anything closer than this is quite beyond the pale and cannot even be considered.” (Otherwise an excuse will be found even for full-sib matings.) If the available population diversity within your own breed allows you to draw the line further out, so much the better.
COEFFICIENT OF INBREEDING
To avoid frank incest matings within the first three generations of pedigree is not enough in and of itself. The Coefficient Of Inbreeding (COI) must also be monitored, preferably over at least eight to ten generations of the known pedigree, keeping it as low as possible. To do this over more than two or three generations requires the use of computer software such as CompuPed, Breeder’s Assistant, FSpeed, etc. (To calculate a four to six generation COI only gives a false sense of security; usually such a COI fails to tell the whole story, and the ten-generation COI will be found to be dramatically higher.) In a purebred dog breed COI can hardly be too low; almost always it is far too high! It is impossible to recommend an arbitrary figure for percentage COI, because the situation of each breed is likely to be different. Probably anything greater than 5% constitutes a distinct threat to genetic health, yet setting the bar at 5% may be virtually impossible in many breeds. There are breeds in which breeders may have to make great efforts to get it as low as 20%; in at least a few breeds 20% would be alarmingly and needlessly high. But breeders should KNOW what the average 10-generation COI level is for their breed, at least, and seek to keep their own breeding well beneath that average level! Otherwise the COI just goes on indefinitely, increasing steadily year by year. It is easy to point to specific individuals in numerous breeds with COIs of 70% or more, but it would be a real challenge to produces examples of less than 5% COI in many breeds. One ought to take care that the COI trend in one’s own breeding is never upward, but always either downward or at worst neutral. This is done by averaging the individual COIs of sire and dam (add the sire’s COI and the dam’s COI and divide by two) and then comparing this average with the COI for the trial mating or litter that would result from mating those two individuals. If the litter COI is higher than the average of the parents, then you are obviously increasing the overall level of inbreeding by performing that mating, and the greater the disparity between the two figures, the more the mating should be deprecated. You may also wish to look at the same data from a different perspective by calculating (with the same pedigree software) the Coefficient of Relationship (RC) when examining trial matings, the more easily to ascertain which of two or more alternative matings has the least-related parents.
NUMBER OF UNIQUE ANCESTORS
You must use a breed database in conjunction with a pedigree and COI application such as Breeder’s Assistant or FSpeed to explore COI and trial matings. When you do so, you should also use it to study the number of unique ancestors in the known pedigree, the number of ancestors in common between sire and dam, and the number of ancestors unique to each parent. These figures are useful in assessing the potential diversity of a projected mating and will tell you more than the simple COI (which, after all, is only a percentile probability figure predicting the likelihood that alleles at the same gene locus contributed by the sire and dam will be identical by descent).
Also try to carry out in-depth pedigree analysis for every mating, listing the major ancestors on which inbreeding occurs in that mating, noting the number of occurrences and the generation number of each occurrence. This analysis should be carried back for at least six ancestral generations, ideally for eight. This practice will alert the breeder to undesirable “pile-ups” on key animals and therefore to potential genetic problems (if such are known to be associated with such individuals) in the planned mating. An alternative or supplementary approach is to use the “percentage of blood” function of pedigree software such as Breeder’s Assistant.
Instead of inbreeding, use assortative mating (mating unrelated parents who are phenotypically similar for the desired traits) to emphasise or fix greatly desired traits. Assortative mating is much less dangerous than inbreeding and will accomplish much the same ends. It should be obvious that to breed “like to like” for given desired traits will tend to yield more of what is desired, but if the parents are not closely related, there is a greatly reduced chance that other unconsidered traits will be unknowingly reinforced by such matings.
Genetic losses occur almost infallibly with each generation in purebred dogs, whether those losses happen through random drift, from too few progeny contributing to the next generation, from the inbreeding/selection cycle, or whatever. For that reason, the fewer the intervening generations that occur between foundation stock and current stock, the less genetic diversity is lost. Breeders should therefore maintain a high average generation time (age of the sire at mating plus the age of the dam at mating, divided by two) for each litter produced: four years should be considered an appropriate minimum floor level, five or six is better. It is helpful to calculate a running average generation time for your kennel throughout its history, by keeping a grand average of the average generation times of all litters produced.
Do not always use the same sire for a particular bitch (or vice-versa). Many kennels make a routine practice of repeating favourite breedings over and over again. Take care to maintain diversity in your matings. Endless repetitions of the same matings greatly reduce the available breeding combinations both within the individual kennel and for the breed at large.
Try to ensure that at least two of every litter (unless it should happen to be one of those litters that had best be forgotten) contribute to the next generation; half the litter should be the ideal, though perhaps a difficult one to maintain. In every instance in which only one progeny from a given mating contributes to the next generation, automatically and infallibly 50% of the available genetic diversity in that line is permanently lost! If two progeny contribute the theoretical average loss is reduced to 25%, still less if more littermates contribute. This single point is a major source of losses of genetic diversity, yet it often goes totally unconsidered by the breeder.
Monitor key indicators of survival fitness in your canine stock. These are fertility (percentage of successful matings), fecundity (average litter size compared to the norm for your breed), birth weights, nestling viability, survival to adulthood, and longevity; be sure that your breeding programme does not trend toward the reduction of any of these.
It may be valuable to try to balance the relative contributions of founders (where possible and appropriate), particularly subsequent to founder events or genetic bottlenecks. “Founder” is a relative term. If a breed has a long pedigree history with original breed foundation stock at thirty or more generations remove from current stock, it may well be impossible to balance the contributions of the original breed founders; their relative contributions may already be set in stone for all practical purposes. But founder events tend to occur repeatedly within the history of a breed. Bottlenecks occur with dismal regularity. At least the breeder can pay attention to the most recent founder set that is clearly identifiable, attempt to prevent the loss of individual founder lineages that are seriously under-represented, and seek to balance the relative contributions. Clearly this is no simple matter and to suggest that it be applied consistently may be a counsel of perfection. At least it is one more possible tool in the breeder’s armoury against diversity losses.
The great majority of dog breeds have been bred within a completely closed studbook for sixty to a hundred years, with little or no fresh genetic input throughout the entire period from breed foundation to the present. Similarly, many individual bloodlines have been treated in exactly the same way, bred in relative genetic isolation from other bloodlines. Each breeder ought perhaps to consider the desirability of locating and using a true outcross within his or her own breed (unrelated to one’s own stock for at least ten to fifteen generations) at least once and to integrate the resulting progeny into one’s bloodline. If there is any possibility to import unrelated stock from a breed’s country of origin, one ought seriously to consider doing just that. This is mainly possible in the case of landrace breeds, in which an autochthonous regional population remains in the country of origin, independent of exported stock that may have become a registered breed in other countries. Examples of such situations would be the population of desert-bred coursing sighthounds in the Near East, relative to the Saluki breed in Europe and North America, or the relict populations of autochthonous arctic spitz-type sled dogs relative to the modern Siberian Husky, Alaskan Malamute, Samoyed, et al. It would be difficult to overestimate the genetic value of a single import animal, unrelated to the “registered” breed population for scores of generations but stemming from exactly the same fountainhead. This I would term the “Holy Grail” of the diversity breeder — the ideal controlled-outcross situation in which an immediate significant increase in healthy genetic diversity may be obtained at little to no cost in terms of breed type and purpose. (That the Canadian Kennel Club rejected this option for the Siberian Husky in 1994 demonstrates, I believe, the true extent to which the umbrella all-breed registries represent an obstacle to genetic health and true breed improvement.) In cases of small, highly-inbred populations for which there is no landrace resource, it may become necessary to consider an outcross or outcrosses to similar breeds. If so, this ought to be faced squarely and proactively by the breed club concerned and breeding subsequent to the breed outcross ought to be a collective endeavour, shared for purposes of more thorough integration and to reduce the work-load on any one breeder — because, no question about it, the integration of a breed outcross is a major task that can hardly be undertaken alone by the average breeder. (The Backcross Project in the Dalmatian breed was an excellent example of a breed outcross well-purposed and superbly integrated; but the reaction of the breed club was deplorable.)
In the case of small, developing breed populations, it should be regarded as important to monitor and control the growth of the population (in number) such that there is steady expansion of the population within the limits of breeders’ kennel capacity and the demand for progeny. Growth by fits and starts, with overexpansion followed by sudden cutbacks or population collapse, is very bad for genetic health. It is difficult, at best, wholly to avoid population bottlenecking. But its existence and ever-present possibility should be recognised and to whatever extent may be possible, breed clubs and the individual breeders should do whatever they can to ensure smooth, steady population expansion and to minimise cutbacks and consequent genetic bottlenecking.
One ought always to evaluate breeding stock for balanced characteristics: health, vitality, temperament, working ability, intelligence, structure, type. Breeders should aim to maintain the balanced characteristics of a total dog, not just to produce winners at dog shows, field trials, races, etc. An all-round, balanced dog will be a much better hope for the future than a highly-selected, over-bred dog that is thought to be “best” due to possessing exaggerated traits in one or two areas, whether it be a “perfect head,” a showy gait, a faster racing speed, or whatever. First, each individual needs to be a good dog, and that should come ahead of breed considerations.
UNFIT BREEDING STOCK
It ought not even to need saying — but in these days in which extensive, heroic and expensive veterinary measures are routinely used to save otherwise doomed animals, it does need saying: the breeder ought never to breed from dogs that would not be alive but for such interventions (excepting, of course, survivors of physical injuries). It should be obvious that if we prevent the operation of natural selection, many of the animals that we use for breeding purposes are likely to pass on various transmissible genetic weaknesses.
Breeders should also consider whether it is in their breed’s interest routinely to use elaborate reproductive technology to produce litters. These days various and sundry technical means are available which circumvent natural mating and whelping. Some breeds, indeed, cannot either mate or whelp a litter without veterinary intervention — already! If we use artificial insemination and hormone assay to effect mating combinations that cannot be brought about by natural mating, along with routine C-section to deliver litters, we may rapidly find ourselves in the position of having created strains which cannot reproduce naturally without technological support. We should also consider whether it is really a good thing to freeze the semen of outstanding males and thus extend their breeding life decades into the future; this practice seems to be universally approved, while no one appears to have examined what effect such extension of the influence of individual stud dogs might have on breed genomes.
This may really be the most important principle of all, and the most difficult for the vast majority to accept. Breeders should avoid all extremes of artificial selection! When one comes to consider the problem of lost genetic diversity, inbreeding by itself is only half the story. The hard truth is that selection itself is just as great a culprit, if not worse. Inbreeding and selection combine together in a cyclical fashion in the dog world to cause the systematic depletion (“depauperisation” to the geneticist) of purebred genomes. The desire for a cookie-cutter “consistency of type” causes healthy genetic diversity to be discarded intentionally at an alarming rate. (An example of this desire is the person who declared at a Chinook specialty show that he saw at least five different types represented there, and that “they had better get themselves a geneticist or they will never have a standard type.” The Chinook is a working breed with a dangerously low population and a perilously narrow genetic base; the kind of diversity that engendered that comment is hardly to be deprecated in such circumstances.) We hear endless discussion about inbreeding and its evils, and rightly so; but we hear very little about the dangers of sustained extremes of artificial selection, which are if anything yet more dangerous than inbreeding. Together these two factors become an engine of destruction for genetic diversity. The constant obsession with having the “best” dog and with “breeding only the best to the best,” whether in dog-show terms, in dogsled racing, or whatever, creates a situation in which the best is definitely the enemy of the good. The endless repetition of the inbreeding/selection cycle in the quest for a dog that is better than last year’s best, has systematically stripped away most of the healthy genetic diversity from today’s purebred dogs. Stringent, sustained selection for cosmetic ideals (shape, number and intensity of the Dalmatian’s spots; shape and chiselling of the poodle’s muzzle; subtleties of colour and markings in an endless series of breeds) or narrow ideals of performance or athleticism (top sprinting speed in racing greyhounds or racing sleddogs) have for many decades taken absolute precedence over breeding to provide the kind of “genetic outfit” that will allow the dog to be healthy and hardy. Now that canine diversity has been stripped to the point that homozygous recessive “defect” genes are everywhere apparent, the dog fancy proposes to remedy the situation by embarking upon a new level of elevated selection, armed with DNA marker testing to enable the wholesale “elimination” of “defective” genes. This new wave of super-selection on top of the already extant depauperisation may well become the killer wave that will sink the entire ship of purebred dogdom, AKC, CKC, and The Kennel Club with it. DNA testing has become a growth industry. This all may be more about corporate profits and grant money, than about genetic health. It is up to breeders to have the common sense to realise that what is being proposed is a losing game, that already depauperate purebred breed genomes will not support further massive artificial selection and the consequent wholesale elimination of yet more genetic diversity. The “defect” genes cannot be excised with a scalpel; many other genes that happen to reside on the same chromosomes will go right along with the defects, with totally unforeseeable consequences.
In conclusion, let me say that, although this set ofguidelines cannot be made into hard and fast rules or (worse yet) regulations — because the situations of each individual dog breed and even each breeder are different — yet I believe we all need faithfully to attempt to apply the principles discussed above, in order that our dogs may have long, healthy lives upon the earth. We should strive to be faithful stewards of the genetic heritage of our canine friends. In that way we may hope that our bloodlines will endure longer in the dog world, and in the end we may even be remembered as pioneer 21st Century dog breeders who strove heroically to correct the errors of the past in the light of better knowledge of population genetics.”
~ J. Jeffrey Bragg