BREEDING DOGS FOR THE NEXT MILLENNIUM
Dr. Hellmuth Wachtel 1997
The evil might of hazard - nobody knows when it will strike - Of coins and breeds
What has pure chance to do with the fate of dog breeds? Quite a lot.
An everyday example may illustrate this:
If you throw a coin, you have two
options for the outcome, but only one can turn up. One alternative
necessarily fails. If you throw six times, chances are that you get
both options, but in different numbers for each. Hardly you will get
both faces up six times, so one face will "win" over the other, or with
other words, some options of one face will be "lost". Throw a hundred
times, and there probably will be both options in about equal numbers.
The higher the number of throws, the closer you get to a fifty-fifty
ratio, provided the result is not biased by a defective coin that makes
it fall more frequently to one side. In a million casts, the deviation
from a half-half distribution will be insignificant. That means, the
more throws, the lesser the power of hazard to produce an unequal,
biased result of the two options.
The same happens genetically to a
breed. If the breed is very small, the 100.000 gene pairs with 200.000
single genes (alleles) of each dog are "cast" with every new
generation, that means freshly distributed. Chances are, that
comparably to the coin example, some alleles of gene pairs in the
populations get lost, others increase correspondingly in number, and
finally one allele might completely vanish from the breed while the
other holds the field, it is "fixed" in the population. Ok, there are
still 200.000 alleles in the cells of all these dogs, but now many more
allele pairs consist of identical alleles, and if some of these are
defective, the dog will suffer from some disorder, sometimes even a
deadly one. Besides, many genes yield more stamina and viability if
there are two different alleles per pair.
Every breed is a "rare breed"
The greater the effective breed
population size, the smaller the number of allele types lost or fixed
in that way, the less the risk of a substantial deleterious change of
the genetic situation. Effective population size means that a breed
population may consist of many thousand dogs but if the breed was
founded by a handful dogs and/or has been heavily inbred, it contains
relatively few different alleles, so in effect a breed of several
million dogs like the German Shepherd Dog may have an effective genetic
population of just 500. In such a breed, the inbreeding advance because
of breed size is minimal, but the inbreeding level resulting of the few
founders and subsequent inbreeding or stud over-use will be relatively
high. Thus, genetically seen, even the world's most popular breed is a
"rare breed", and so are all the rest. Natural animal populations, by
contrast, mostly have effective sizes of many thousands or even
millions.
In the last decades genetic science
has undergone a revolution that has given us a better understanding of
how nature is governing the fate and evolution of animal populations.
The secret to health and viability of wild animals is permanent severe
selection plus high genetic diversity. Therefore, by contrast to what
is commonly believed, most animals use diverse strategies to avoid
inbreeding. Wolves, for instance, partly leave the pack as young adults
being expelled or voluntary, and roam long distances (hundreds, even
thousand miles and more) in order to find a non-related partner to
found a new pack and a new territory or a pack that is willing to admit
them. Inbred wild animals would be handicapped in the struggle for
survival and mating partners so nature favors outbreeding behavior,
even in species where few males reproduce (harem pashas). In these
cases, the male turnover is rapid due to exhaustion, and often they are
not able to effectively watch over
their females. So short active periods before being replaced by a rival
prevent mating with daughters. There are few mating males at any
moment, but still rapid replacements provide for many mating males per
time period. The creation and breeding of purebred dog breeds is based
on an entirely different system with detrimental consequences: in
creating today's breeds, a few animals of a characteristic strain, a
"landrace", were selected that were highly typical. While showing some
basic traits in common, these landraces were rather heterogeneous. The
few selected animals were inbred in order to fix the desired
characteristics. Sometimes, different looking strains were crossed in
order to create an entirely new type.
Again, the few resulting animals
showing the right type the breeder wished to materialize were inbred to
stabilize the result. So, new breeds were born. This happened about
hundred years ago with most breeds. Since then, they became "pedigree
dogs" and no crossbred or unregistered dog was anymore accepted to the
stud books. Thus breeds were kept in a "golden cage" losing genetic
variety ever since for the reasons described above (stronger hazard
effect plus actual inbreeding and over-use of far too few studs). The
results is seen in better health and longevity of mongrels, but
appropriate state of the art breeding and selection would produce dogs
that are even healthier and live longer than mutts, a goal sound
breeding ethics prescribes. Incest - not only an abomination in humans
It was soon detected that incestuous inbreeding could create a hoard of
problems. Highly inbred animals became delicate, easily sick, sterile
or showed other defects. So breeders learned to be careful with matings
between close relatives, and sometimes it became even necessary to
outcross. This immediately remedied all problems, but often hampered
the breeding progress. If during the inbreeding period, animals showing
defects or diseases were carefully culled, the breeding lines were
actually "cleansed" of the most deleterious genes. So, the general
conception of inbreeding was to be a very effective and essential tool
for achieving any breeding goal, being harmless, even useful for the
health of the breed if appearing defects were severely eliminated.
Often just one dog showed all the desired breed characteristics to such
a high degree, that this one, having won high awards and championship,
was wanted as a sire by many breeders, sometimes most or all of the
bitch owners of that particular breed. Often this stud turned out to be
a prepotent sire, improving the conformation or performance of part of
or the whole breed. But this prepotency was mostly the effect of the
genetic depletion of this sire. As he had little more to transmit than
his own good looks and other traits, he could not transmit any
undesirable traits to his offspring. In biological terms, however, he
is not "prepotent" but biologically inferior. Sometimes it happened
that the dog world did not like the current look of this breed any
more. So the standard was modified or just otherwise interpreted by
judges, clubs and breeders. As standards are just descriptions, there
was room enough for everybody reading it to get a different notion of
what this breed should look like. In fact, just by reading a standard
it is difficult or impossible to get a realistic idea what the breeds
looks like, if you have never before seen a dog of this breed.
These changes of breeds can be seen
if we look at old pictures and new ones of the same breed. Sometimes
one should think the dogs belong to different breeds. A change of
characteristics required a special selection for the new traits ensued
by increased inbreeding to fix them in the breed. As very few dogs
showed the characteristics of the new type, only these were now
suitable for further breeding, especially of course those males that
were the best representatives of the new type.These were again heavily
used as studs. Quite often it happened that a breed lost its specific
working task and became nearly extinct, e.g. the Irish Wolfhound, or
the Saint Bernard. Or, in wartime, people could no longer afford dogs,
especially of big breeds, so again these were threatened of extinction.
When renewed interest or improved economic conditions allowed to
produce dogs of these breeds again, just a few were left to start anew
building up a population. Now let us see what happened genetically in
our pedigree breeds. They were and are continuously subject to close
breeding. While "close breeding" is often used to designate
"incestuous" matings (brother-sister, parent- child) I mean to
characterize all those breeding practices that decrease genetic
diversity, i.e.
* (i) close inbreeding (incest) * (ii) mild inbreeding (line breeding -
uncle - niece, aunt - nephew, cousins, etc) * (iii) too small numbers
of studs in breeding populations and their highly disproportional use *
(iv) shrinking gene pools due to changes of breed characteristics
(revising or reinterpreting the standard) * (v) the case of rare breeds
* (vi) "overstandardizing" breeds, as this too eliminates the necessary
genetic diversity (polymorphism)
All this adds up in permanent
accumulation of the inbreeding and homozygosity level of breeds, both
real inbreeding as well as all the other practices listed above, so
some of them produce inbreeding effects even if the breeder does not
use "real" inbreeding! So all the cited events and practices used in a
breed's history tended to give rise to genetic depletion. The average
inbreeding level (inbreeding coefficient) of dog breeds is therefore
estimated to have reached 14%. That is about the inbreeding level of
progeny from a halfsib mating, but many will be much higher. In fact,
many breeds constitute family clans, outcrossing becomes impossible.
Any increase of the inbreeding level is a proportionate rise of
identical genes (alleles) in a gene pair resulting in corresponding
higher risks for hereditary defects and diseases. In progeny of sib
matings (inbreeding factor 25%) probability to be affected by a
hereditary defect is about six times higher than in that of non-related
matings, if five percent of the population carry the defect gene! A
friend that tries to keep inbreeding levels low was happy to get down
to an inbreeding coefficient of 6% but was aghast when he was told that
after computer calculation of the breed population the actual
inbreeding coefficient of his dogs is around 30 %, i.e. higher than
that of a sib mating offspring! Breeding pet animals genetically highly
depleted by inbreeding or any of those other practices listed above has
began to cause serious concern in many advanced countries. Holland has
enacted a bill for animal protection stipulating possible bans both on
breeding with animals with a high incidence of severe defects and
methods of breeding that could result in sick or otherwise suffering
animals.
According to a Dutch expert, upcoming
provisions to this law could ban breeding dog breeds that show
increasing severe affliction by hereditary diseases, and line breeding,
being a method that is liable to result in higher risk of hereditary
defects. In Sweden it was proposed to limit the lifetime litters from
one stud between 1 (!) to 100, according to the population size of each
breed. While this proposal was rejected by a majority of breed clubs,
working breed clubs were more positive about it than clubs for show
breeds. The Swedish Clumber Club already fixed this figure to 4 litters
per stud. Moreover, the Swedish Kennel Club is sponsoring an
Interscandinavian Research Project to investigate the homozygosity
level of thirty important breeds by molecular methods like DNA finger-
printing. The results will be most interesting, as they will be
informative on the background inbreeding level of domestic dog breeds
since inbreeding factors calculated from pedigrees are always too low
and misleading. They refer only to a few ancestor generations, the
preexisting background inbreeding level is not shown. In Germany, a
draft expertise on the interpretation of the animal protection law's
paragraph prohibiting matings of pet animals liable to produce disease-
affected offspring has stigmatized incest mating as an infraction.
Inbreeding has a very strong effect
on outbreaks of inherited diseases. If e.g. 5% of dogs in a breed carry
a defect gene without being sick, a dog that has been bred from a
brother- sister mating has an inbreeding coefficient of 25%. That means
it has lost a fourth of the original genetic diversity and its risk to
suffer from the hereditary diseases are 8,6 times higher than those of
a non-inbred dog! So close breeding, while not actually producing
inherited disorders, largely boosts the chances of an inherited disease
to be manifested. As practically every dog and every human carries
several defect genes, this risk is nearly always present. So many
decades of close breeding have brought about high percentages of defect
genes in nearly every breed producing the so-called "breed-specific
diseases". While natural animal and human populations may carry
hundreds or thousands of different defect genes, in individual dog
breeds there are only a few but since a big proportion of the breed
carries defects of the same type, so many dogs of pedigree breeds get
sick. By contrast, in wild animals of natural populations sick
individuals suffering from genetic diseases are extremely rare, as
parent animals while mostly carrying several defect alleles each,
rarely the same ones are incidentally present both in a mating male and
female, so sick offspring is an exception in nature.
Small population size, but also all
the other breeding practices increase the deleterious power of hazard
to make genetic diversity get lost. But as in the comparison with the
defect coin that falls irregularly, the right kind of selection can, if
partly, counteract this effect. In fact, the calculated inbreeding
coefficient is never precisely equal to the actual loss of genetic
variance, for it is subject to incidental variation as explained
before. The meansto keep variance high is selection for health and
fitness, because it favors those individuals that by chance have
maintained a higher level of genetic diversity (there are always some
of these in a larger population). Thus, in those former days of dog
breeding dogs were still heavily exposed to forces of natural
selection: low standards of general and veterinary care or its absence
(no vaccination, poor feeding and care, more use as working dogs, poor
housing etc.) helped to maintain genetic variability for some time in
spite of inbreeding. In the meantime, this has materially changed, dogs
with poor viability may today be raised and successfuly bred on account
of high standards of general and veterinary care. So inbreeding damage
is much more pronounced as biologically inferior subjects enter the
breeding stock (actual genetic loss may thus be higher than the
calculated inbreeding coefficient!)
As a result of these developments,
and most inexpectedly, in 1996 the time-honored mother of modern
pedigree breeding herself, the English Kennel Club, has changed her
basic and principal centennial rule: dogs of unknown or "impure" origin
are no more absolutely excluded from being registrable if officially
admitted! The idea behind is probably the risk that advancing
DNA-testing would disclose that a majority or even all dogs of some
breeds already carry some deleterious defect what obviously could badly
impair a breed's market appeal. Now the only way to decrease defect
gene levels in so highly affected breeds without any reserve of
non-carriers is crossing with a less affected but closely related
breed. In fact this would not destroy a breed's characteristics if well
planned and followedby back-breeding and appropriate selection. On the
contrary, as few as just one strange animal per hundred breeding dogs
and generation in a population would very effectively prevent genetic
losses and thus counteract the advance of inherited diseases and
improve viability, health and general fitness of the breed!
Last year, the International
Ethological Conference at Vienna bore ample witness of how animals in
nature (including man) make sure that their progeny is provided with
that genetic fitness as is necessary to give it the means to withstand
environmental challenges, e.g. the onset of parasites and infections of
all kind. This constant "arms race" between animals and parasites is at
the root of evolution of species. Animals use the costly sexual
reproduction (two animals needed for one progeny) for being able to
throw persistingly new genetic combinations into the battle for
survival. In he majority of cases, inbreeding is of course avoided for
an inbred offspring would be at disadvantage competing with outbred
progeny of other parents.
This requires to dispose of a
heterozygous MHC and possibly a well matching one, which is mostly
achieved by skilful female mate choice: the MHC, the Major
Histocompatibility Complex of genes, is not only responsible for an
animal's immune capacity but at the same time also for its body odor,
thus serving as an infallible indicator ("honest certificate") of a
male's genetic quality as a sexual partner. So by sniffing a female can
easily ascertain if a potential male partner is too near a relative and
if not, if he would make an adequate match to produce good resistance
and competitive strength in the offspring. So far, this phenomenon has
been verified a.o. in mice - and at leat partly, in man, or women, for
that matter. Less smell-oriented animals, like peahens and other birds
see on
their cocks' ornamental feathers, symmetry, and color brightness if
they are genetically eligible or not. This has revealed the vast
importance of female mate choice for the survival of animal species
(including the human race, come to that). The loss of MHC variability
not only decreases vital infection resistance, but poor MHC's even give
rise to autoimmune disease and vaccination accident susceptibility, so
the dog's MHC is currently an object of veterinary research.
Unfortunately, we cannot allow our brood bitches to chose their females
as they would lay little weight on standard and working traits.
Besides, chances are they have lost the selection capacity during the
domestication history, though examples of female choosiness are known
to dog breeders, but hopefully vets will be soon able to substitute
females in this job tofind the right mating matches.
In conclusion, hopefully rigid
"racism" may finally give way to a more competent, enlightened kind of
breeding benefiting from the long-established rules of population
genetics: while maintaining the breed concept, keeping breed
populations genetically variable but allowing for a more natural,
health-conserving approach that rejects inbreeding and over-use of
studs as well as the other deleterious breeding practices. Genetically
variable dogs are more adaptive and resistant to environmental changes
and requirements, better performers, healthier, showing better
intelligence and character. This is called heterosis while inbreeding
causes the opposite, inbreeding depression. Symptoms are loss of
fertility, less resistance, intelligence, performance etc. These
symptoms may but must not occur, but long-time close breeding
invariably must end up in disaster. Breeders may line-breed all their
life and apparently enjoy best results, but sooner or later some
successor will dearly pay the bill for it in form of progeny of poor
health and viability. All those hecatombs of dogs sacrificed every year
for some inherited defect bear witness.
Steps to better breeding for breed
preservationbanning inbreeding (incestuous and line breeding) severely
restricting use of individual studs according to numerical breed size,
i.e.use of many sires no over-typing selection DNA breed studies
investigating actual state of remaining genetic diversity per breed
selecting dogs primarily for performance, health, longevity,
temperament, not just for looks and soundness planning measures for
boosting genetic diversity (use of genetically distant individuals,
planned crossbreeding, combining color and coat variants etc.)
These postulations may appear
revolutionary but they are based on long established scientific
knowledge long applied in any other discipline of animal breeding (farm
animals, wildlife conservation, rare zoo animals). Indefinite seclusion
of breed populations from any genetic inflow as it has been practiced
these last 100 or even 150 years is impossible and seriously
jeopardizes a breeds' survival. The only option would be cloning
champions like the Scottish lamb Dolly, a horror vision that we really
would not wish for the dog our companion for over 100.000 years (if the
recent astonishing molecular genetic research findings are right).
Breeding dogs for the next millennium, Dr. Hellmuth Wachtel 1997