Dr Per Erik Sundgren has been working intensively in Sweden for
over 30 years to try to convince the Swedish Kennel Club and its
breeders that there is a serious need for better breeding planning in
His extensive genetic knowledge took him to the conclusion that all the well known problems in dog breeding are caused by too much inbreeding in many small populations.
He also collaborated with Swedish Westie club (Alliansen) for years the same way.
These dog clubs have already established new breeding rules among which breeding restrictions from stud dogs and inbreeding restrictions.
Since 2005, the Swedish Kennel Club forbade very close mating, such as between parents and progeny or between full sibs, and such litters will consequently not be registered anymore by the Swedish Kennel Club.
Dr Per Erik Sundgren also advises to avoid mating between half sibs, between a dog or bitch with any of their grand parents or to any of their aunts and uncles. This is what have been the normal rules among our selves in most cultures for thousands of years and of very practical reasons. Breaking such rules will inevitably produce an increasing number of children with inherited defects and health disorders. Dogs’ genetic system complies with the same rules as ours.
His contribution to Swedish dog breeding has mainly been to try to teach breeders basic and sound principles of breeding. He has also produced a computer software to make it possible for breeders to see for themselves the total consequences in an entire breed of their own planning, or rather lack of planning, for the future of their breeds.
This dog breeding software in Swedish language in his web site http://www.genetica.se should be one day available in English.
(update: unfortunatly, Dr Sundgren left us 01.01.2010 and his website does no longer exist)
The genetic article you will read below was written by Dr P.E Sundgren in July 2006.
His goal is to explain to breeders the genetic basis for how and why inbreeding hurts populations.
Natural protection of genetic variation
Programs to preserve genetic health in dog
breed have been intensively discussed in Sweden in connection with the
development of breed specific genetic strategies. Why have breed
specific strategies at all become a necessity in dog breeding?
The body of an animal is although it is a unit, is composed of billons of cells. The link between generations is however only one single cell - the fertilized egg cell. Thus everybody involved in breeding ought to know at least some about how the fertilized egg is protected against genetic disorders.
Genes – protein prescriptions
The basic function of a gene is to be as a prescription for the cell about how to build a specific protein. There are about 30-40 thousands of gene pairs and as many different types of proteins can be built by the cell. We all need skeletons, muscles, nerve systems, liver, kidneys and all other internal organs. We also need al large number of hormones, enzymes and signal substances to make out bodies work properly.
It would all be very simple if there were never
any changes in the environment. There would be no need for any changes
in the prescriptions about how to make a specified protein.
At the cell level the threat from eternal enemies
is extremely large. Innumerable micro organisms and viruses are steadily
attacking our bodies.
The Gene system is subjected to three apparently incompatible demands:
Stability to guarantee that all organ systems are working correctly
Balanced variation for entire population to make long term adaptation to changing environment possible.
Individual variation to protect every being against diseases and infections.
During the first about 3-4 billion of years on Earth there were no more complicated forms of life but single cell organisms. The normal way of reproduction was a non sexual simple cell division.
The DNA molecule, the basic element of genes,
is a surprisingly stabile chemical compound which by doubling is
transferred in equal amount to both the new cells after a cell division.
After such a division both cells gets identical genetic make up. But if
all cells get identical genomes there can be no genetic adaptation to
changes in the environment.
Gender and the duplication of the genome
After several billion of years Nature found
a solution the vulnerable system of simple cell division. Cells with
identical gene set up joined two by two creating a new type of cell with
a new type of genome carrying a copy of each single gene.
Cells with duplicated genomes can no longer
multiply by simple cell division. To make the amount of DNA, and thus
the number of genes, constant over generations they have to go through
two cell stages.
The solution by Nature was to create two sexes both having special organs, ovaries and testis, where the reduction of the genome to half the normal size takes place when creating ova and sperms. The central advantage of two sexes is the thus the duplication of genes to avoid disastrous results of damages to single genes.
A system with two sexes has another
important advantage. At the stage when germs cells, ova and sperms, are
created the DNA molecules, which are as long strings, wraps around each
other. As everybody knows it may be a complicated matter to untangle
Most but not all chromosome changes are
harmful. If there is only a minor change in the composition of a protein
due to a mutation, a sudden change in a gene, the new protein may do
well in spite of the change. In rare cases the new protein composition
might lead advantages for the animal.
Male to female bond affects male reproduction
Evolution through out millions of years has
shown that the division of animals into males and females has been
indispensable for the creation of highly developed animals. There is
however a problem connected to the way bisexual mammals reproduce.
Natural selection again found a solution by
creating more or less strong bond between reproducing makes and females.
It does not matter if such bonds are for life or only for one
reproductive season. The effect will be the same.
In Sweden an overproducing male with too
much progenies is called a "Matador". Matador was an intensively used
bull in the northerly part of Sweden. He carried a gene for testicular
hypoplasia, too small testicles, casing reduced fertility.
MHC – the ID card
The cooperation of billions of cells in a
body can only take place if there is a way for all the cells to identify
each other as belonging to the same unity. Otherwise there is no way to
identify enemies and defend the body against invasion of other cells
causing diseases or damages to the body.
Nature has solved the problem by creating a
special set of genes called MHC, where MHC stands for Major
Histocompatibility Complex. Together the MHC genes form the unique "identity
card" carried by all cells of an indivuidual and make it possible for
the cells to cooperate without harming or attacking each other.
The genes of the MHC system create special
proteins on the surface of each cell. It is the special combination of
these proteins that make up de identity code, alike for all cells of an
individual. The cells can "read" each others identity code and cooperate
without any risk with cells carrying the same code as them selves.
It is now obvious that the more unique
identity code an individual carries the better it is protected against
diseases. Pathogenic cells will always try to copy the identity code to
fool the T-cells that they belong to the body.
The basic consequence of inbreeding is to
duplicate genes of the same origin. Such duplication will inevitably
reduce the number if genes with different prescriptions for protein
production and hence also reduce the possible variation of genes in the
Genetic scent signals
Nature has created a special protection against
dangerous reduction of genetic variation in the MHC gene system. Again
the solution is brilliantly simple. The genes of the MHC system take
part in the production of the scent substances called pheromones.
It is important to accept when the bitches distinctly signals that they do not accept a male. The females know better than the breeder if the male carries MHC genes which are favourable for her progeny. Forced mating is an effective way to violate one of the most important protections of genetic variability.
Fertility and inbreeding
Most breeders are well aware of the fact that strong inbreeding has negative effects on viability, health and fertility. But what are the common causes affecting the immune system as well as reproduction making both susceptible to inbreeding.
The feotus is protected from being rejected
Everybody is well aware of the problems in
transplantation surgery to get the receiver accepting foreign tissue.
The basic reason for the rejection of foreign tissue is that all it
cells carries another ID code and hence they will be attacked by the
immune system of the receiver to avoid an unwanted invasion of possibly
The genes of a fertilized egg are to 50 %
inherited from the mother and tom 50 % from the father. Hence the
genetic system of the fertilized ova normally deviates to a large extent
from that of the mother. As a consequence the fertilized egg ought to be
repelled by the immune defence system of the mother. As a matter of fact
should there be no other mechanism at work pregnancy would not be
The protection of the foetuses has a
negative side effect. At the time when the delivery is finished the
protective protein still remains in the body of the mother for 2-3 days.
During these days she is extremely susceptible to infections since her
own immune response is seriously lowered by the remaining protective
One might think that foetuses with gene
systems very like their mothers, i.e. for example those that are heavily
inbred, would benefit from their genetic likeness to the mother. There
should be a less strong tendency to reject such foetuses from the womb.
How should the uterus of the mother be able to identify fertilized eggs as deviating from any other cells of her body floating through? The different genotype of the fertilized egg and the mother is most certainly one of the prerequisites for the formation adhesion of the egg to the uterus wall and the formation of the placenta.
Another risk with to much genetic likeness between the mother and her progeny is that the labour pains during delivery will be seriously lowered leading to a prolonged time of delivery.
There is thus a threefold advantage in divergent MHC genotype between the mother and her progeny. The foetus will get a better start in uterus of the mother, the delivery process will be shortened and thus less trying and finally the new borne animal will have a more unique ID code making it more viable and less prone to get infectious diseases.
Number of puppies and size of the mother
One of the fascinating consequences of the
fact that the total foetus tissue has a rather close relation it the
size of the mother is that affects litter size in dogs. Normally there
is a negative relation between size of the mother and number of
progenies in al litter, i.e. the larger the mother the fewer her progeny
in each litter.
The ova and her selection of sperms
Is there any way in which an unfertilized
egg may have any influence upon its genetic variation after
fertilization? Anybody who has seen pictures of egg just before
fertilization knows that the egg is surrounded by a crow of sperms.
It might sound strange that an unfertilized
egg should be able to select the sperm that is allowed to fertilize her.
But fertilization is not a violent process where the sperm forces its
way into the egg.
Similar mechanisms are since long well known in cross-fertilization in plants. If pollen form the flowers of a plant reaches the stigma of flowers on the same plant the pollen tube will not grow due to blocking chemical reactions. Thus the stigmas if flowers are able to identify the genotype of pollen and avoid close inbreeding and self fertilization.
The large number of sperms produced by
mammal males has the same function as the large number of pollen
produced by plants. It gives the female egg the possibility to select a
partner producing progenies with the highest possible viability.
Artificial reduction of number of sperms
The very large number of sperms normally
produced by a male has since long been seen just a surplus overflow with
none or futile effect in breeding. The argument behind seems to have
been that as there is need for only one viable sperm to fertilize one
egg why not try to make fertilization more effective.
In breeding with cattle using artificial insemination one normally dilutes the ejaculate 1/100, i.e. the number of sperms will reduce to only one hundred of the normal number. Although such a reduction may not have any dramatic short term effects it is obvious to anybody thinking clearly that in the long term perspective the effect might be deleterious to the genetic variation and thus to the viability of animals.
With our selves the experimentation has gone
much further. It started by test-tube fertilization. With this method,
as when insemination, the fertilization as such is quite normal although
the number of sperms is often reduced.
The fact that it might not be possible to
immediately, or in a few generations, detect serious negative effects
due to such violent break down of natural security mechanism is not a
proof of that the technique is not harmful in a longer time perspective.
Surplus of eggs at each mating
Among multiparous animals there is also
another and simpler mechanism to enhance viability among the new borne
progenies. The number of ova shed by the females during the heat period
is normally about twice the number ever born as fully developed young
Natural selection, or the forces applied by nature
to make individuals as viable ass possible in their environment, will
not preserve genetic variation in all genes systems. In some cases there
is need for genetic stability.
What we in everyday speech call the natural
selection is a force with the purpose to balance the genome to give it
the best combined effect on viability. In nature a creature has to find
food, protects itself against enemies including micro organisms.
It is of profound importance that all breeders of
animals do understand that the basic principle of natural selection is
to stabilize the genetic system to be effective during normal
Normally there is genetic variation in systems
responsible for body size and form, colour, length and thickness of the
fur and so forth. Those are example of characteristics that it may be
favourable to be able to change rather rapidly if environmental
conditions undergo sudden changes.
In wild animals the selective force will under all
normal circumstances be directed towards the centre of the population –
the average individual is rewarded. Extreme individuals may have
advantages only in cases where the environment changes dramatically.
In Nature a stabilizing selection, adapted
to small and slow environmental changes is the normal state. The rapid
environmental changes are rare but most of them cause widely spread
extinction of living species.
Artificial selection is the selection of
animals by man. When breeding farm animals there is a steadily ongoing
selection for faster growth, more milk or eggs and meatier animals. The
most extreme individual are those who win the race provided they are
able to cope with the burden of rapid change placed upon them.
If we seriously want to breed and rear healthy and
vital pet animals we have to learn all the ways Nature preserve
viability in wild animals. We must abandon breeding techniques that
invariably violates all the security mechanisms invented by Nature.
Summary and some practical consequences
At this stage it ought to be evident that
the overriding cause to genetic defects and inherited diseases in
animals not is due to some unhappy coincidence. It is the direct and
unavoidable consequence of lack of knowledge among breeders about some
basic rules of Nature.
Those who are looking for advanced breeding programs to correct all the genetic problems we see today are looking in all the wrong direction. They should try to understand exactly what has gone wrong and start to learn form Nature how animals can be kept viable over hundreds and thousands of years without any theoretical knowledge at all.
The size of a population must be large enough to carry and preserve genetic variation. There is no way to succeed when breeding population having les than about 100-150 breeding animals and twice the number is preferable.
Only viable animals in good physical and mental condition and all natural functions still present should be allowed to breed.
In highly developed creatures the basic rule is that separate individuals are not allowed to have more than a restricted number of progenies during its life.
Those are the three simple basic rules of Nature, rules when properly applied will keep any population of animals healthy over very long time periods. The one and only reason for the genetic disorders in our breeds of dogs and other per animals is that we neglect to consider the mechanisms to protect genetic variation created by natural selection during billions of years.
Sprötslinge, July 2006