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).
Click here for other articles by Dr. Wachtel on:
Diversity- FAQs
Reconstituting
a Breed