Breeding for
the New Millennium
First published in Double Helix Network News, Winter
2000
by
C.A. Sharp
Whether you think the Millennium began in January 2000 or ends in December of
this year, it’s a good time to take a look at the science of genetics and the
breeding and exhibition of dogs to determine where they’ve been, where they
are, where they’re going and how each relates to the other.
Fortunately, we don’t have to go back a thousand years to recap past history in
any of these areas. Genetics didn’t even exist before Gregor
Mendel grew his pea plants in the mid-19th century. By interesting coincidence,
the breeding of dogs and exhibitions featuring dogs had some significant
developments at about the same time.
For most of dog’s history with man, planned breeding—as opposed to the
happenstance random matings that have always and
still occur among dogs—was done largely on the basis of performance though
societies with a wealthy leisure class sometimes had companion breeds who were probably selected for physical appearance and
temperament. Most dogs had to earn their keep, so good hunting dogs would be
bred to other good hunting dogs, good herders to good herders, etc. with
emphasis put on particular aspects of those traits that were useful to the
people in the time and place they were bred. Pedigrees might or might not be
kept, depending on the inclinations of the breeder or the culture in which he
lived.
In the 19th century, social thinkers strongly promoted theories relating to the
importance of ancestry to the quality and character of the individual.
"Purity" of blood was considered an asset for both man and beast. In
this thinking lay the seeds of our present system of closed breed registries
and the prevailing attitude that any mixing of breeds, for whatever purpose, is
a threat to the well-being of the parent stock on both sides. "Like begets
like" was a breeders' mantra.
The challenge, "My dog’s better’n yours!"
has no doubt been with us since dog first allied himself with man. Canine
competitions both casual and formal have been a feature of a wide variety of
human cultures, but prior to the 1850s, these were performance competitions. At
this time the exhibition of dogs in conformation shows was established, based
on similar pre-existing exhibitions of livestock. The original purpose was to display
fine specimens of the various breeds in a venue where other breeders and the
general public might view and them. The competitive aspect was considered an
enjoyable secondary benefit.
Over the past 150 years, dog breeders have continued to produce dogs with the
intent of "improving the breed," though the definition of what
constitutes "improving" is a subject of hot debate. As changes in
technology eliminated or at least drastically reduced the "work"
available for dogs and the need to produce dogs which could perform that work,
most breeders have focused on producing companion and/or conformation show
animals, though a significant minority still focus on the functional aspects of
various breeds.
Competitive events continue to exist and have probably grown in popularity, at
least in
While the dog world has been evolving steadily on it’s 19th century
foundations, genetics has exploded. Gregor Mendel’s
work went largely unrecognized until the turn of the last century. For the next
fifty years, what was known about genetics was based largely on observations of
what was produced by particular crosses or how a trait was distributed
throughout a pedigree. Then, in 1952 Watson and Crick discovered the
double-helix structure of DNA. Since then, cascading technological improvements
have allowed scientists to delve into the detailed structure of DNA and the
chemical processes by which it functions, both for good and for ill.
As genetic knowledge became available to the public, breeders began to apply
basic concepts to their efforts. Words like "dominant" and
"recessive," and even mouth-twisters like "homozygous"
became standard breeder jargon. Those whose breeds could have variations in color or coat type quickly learned how such traits were
passed and what kinds of crosses would produce them—or not produce them, if
they were undesirable. The old notion "like produces like" was
confirmed by genetics. And if it didn’t produce like, then there was a
recessive that one must breed out of one’s line.
To maintain the quality of a line, breeders have for decades bred related dogs
to eliminate "bad" recessives and make "good" genes
homozygous, on the theory that if all the good genes were concentrated and the
bad ones strictly eliminated, the line could only improve. Most breeders are at
least vaguely aware of Something called "inbreeding depression" and
will seldom or never make matings that would be
termed "incestuous" in humans and they will outcross to dogs they
consider to be little related to their own every few generations.
The "quality" which most breeders hope to achieve is keyed largely to
“breeding to the standard" or success in competitive events, especially
conformation shows. Health issues are often not prime selection criteria,
beyond screening for a few specific ailments known to occur in a breed. At one
time, dogs with marginal health or soundness would be eliminated from the
breeding population by nature or their inability to perform. Today, with few
opportunities for screening via vigorous and demanding physical activities and
with veterinary medical advances which allow dogs which would once have died or
been unable to reproduce to become parents, animals of marginal health can
become part of the breeding population, sometimes without the breeder even
being aware of their shortcomings.
The show culture confers the mantle of greatest success on those who produce
the most winning dogs and the dogs which individually win most often. Some
breeders allow the gaudy bubble of big wins become the guiding light of their
breeding program, beside which all other considerations pale. When such
individuals are successful in producing winners, others buy dogs from them. The
more successful they are the more will seek out their stock., at which point
the various negative traits they may have ignored in their pursuit of show wins
can become wide-spread in a breed.
Meanwhile, genetics marches on. We now know that dogs have 80,000 genes or
more. We know that many of these genes, perhaps as many as 95%, determine that
what we have is a dog, not a zuccini. Of the balance
(at least 4000), some determine that our dog is an Australian Shepherd, rather
than a Borzoi or a Papillon. The breeder will have
little affect on these because they are
"fixed" for dogs or for his breed. But that still leaves a few
thousand genes to deal with, not a number easy to keep track of.
New discoveries and, more important to dog breeders, new screening tests for
genetic diseases are announced with greater and greater frequency. Some breeders blythely await the day
when once can screen for "everything" with a simple blood sample and
all dogs with defective genes can be eliminated before they are bred.
Unfortunately, that day is not here and is not likely to be for a long time.
Such DNA tests as are available are often breed-specific and expensive. To make
best use of available testing and such new screening tests as are developed,
breeders need to educate themselves on the strengths and shortcomings of each
test, determine what it costs and analyse how much benefit their dogs and their
breeding programs will derive from each test. For instance, if the percentage
of false positives or false negatives is high, it is only marginally useful as
a screening tool. If the cost of having the test done is high and the disease
is rare in a breed, is it really beneficial if a line has no known history of
that disease?
By becoming informed consumers, breeders can make the best use possible of the
technological advances that genetic science provides. But while many people do
their best to be savvy consumers, our relationship with science tends to be
love/hate. We embrace wholeheartedly those scientific discoveries which support
our personal view of life and the world, but those which are inconvenient to
our belief systems are shunned. This applies to dog breeders no less than to
society as a whole. Once, when the author was trying to explain to a breeder
how an unwanted color had occurred in a litter, the
breeder informed her, "I don’t believe in that genetics stuff." While
this case is an extreme one, it serves as a caution to be open to the
consideration of new information even if it is presently inconvenient or
appears to negate a dearly-held Truth.
Like begets like, therefore closed registries and linebreeding
should guarantee the continuation of traits we hold dear. Or will they?
In spite of the best efforts of generations of breeders, genetic disease is on
the rise in purebred dogs. Not just in one breed, but in most of them. Some of
this is attributable to mis-placed priorities, such
as the previously mentioned focus on show wins. A significant portion is due to
the culture of denial which demands secrecy about such matters and punishes
those who speak publicly about diseases that have occurred in their dogs and,
especially, what the pedigrees of those dogs were. But at bottom, the problem
exists because we cling to a breeding modality based on cherished but outdated
notions of how to breed better dogs.
By closing registries we have, in effect, created "islands" for each
breed. While new individuals (and their genes) may reach these
"islands" via imports or other means, the "new" individuals
are often to a greater or lesser degree related to those already in the closed
gene pool, particularly if the existing population is long –established. The
gene pool is what it is and one has to make the best of it.
But what happens when the "environment" on those single-breed islands
dictates that some of the population will not reproduce? The genes those
unacceptable individuals have will be lost if few or none of the other members
have them. If the dog was not bred because it had a serious disease or gross
physical deformity, it is probably best removed from the breeding population.
But what if the dog is only related to one with such a disease or deformity,
with no certain knowledge as to whether it did or didn’t carry the genes for
the problem? Or what if it had a strictly cosmetic fault, such as an unwanted color or a less-than-perfect coat type, earset
or tail carriage? Elimination of dogs with minor faults or which are only
suspected of carrying faults can also eliminate the positive genes they carry.
Long study of island species has shown that they can flourish, even though they
descend from very few founders and are, necessarily, highly inbred. But Mother
Nature culls more harshly than any dog breeder. The unfit and even the
marginally fit are not likely to survive to breed. And her ideas of
"fitness" have much to do with physical health and soundness and only
slightly to do with who is best looking. Even so, island species are often devastated
by the introduction of genetically more diverse mainland species that either out-compete the island populations, prey heavily upon
them, or introduce diseases to which they are resistant but the island
creatures are not. The average purebred dog will only occasionally be
"out-competed" by a trendy new import and it isn’t likely to become a
new breed's preferred entrée, but it can be more susceptible to infectious
disease.
Study of the genes which govern the immune system of mammals has revealed that
genetic diversity is key to species survival. These genes are often quite
diverse, having as many as 100 different forms. Any individual dog can have
only one or two types of allele for any of these genes, but the species as a
whole has many. So, when a new canine plague comes along—as it did with
parvovirus in the late 1970s and early 1980s—many dogs will die but most will
survive. But our different breeds, on their various purebred islands, may or
may not have the genetic machinery needed to cope.
Since the most variability any one dog can have is two alleles, if a breed has
only a few founders, went through a genetic bottleneck due to war or some other
disaster, or has been highly subject to the use of popular sires, the diversity
of immune system genes may be quite limited.
All purebred dogs are, of necessity, to some degree inbred. They all descend
from an ancestral population which was probably regional and which exhibited a
group of traits which people found useful or attractive. How inbred they are
depends on a variety of factors: How many founders there were, the history of
the breed’s population (bottlenecks, geographic isolation), and who got bred to
whom as well as who got to breed more than someone else. The trick to
maintaining overall breed health is to hang onto as much genetic diversity as
is possible within the existing population. But our breeding practices almost
guarantee that with each generation more genes will be lost.
Many breeders do not realize how inbred their dogs actually are. When degrees
of relationship are considered, only three to five generations of pedigree are
reviewed. But if the generations just off the pedigree contain the same names
over and over, a "loosely-line bred" dog may have an inbreeding
coefficient equivalent to the result of a parent/offspring mating. The use of
popular sires exacerbates this situation. When many breeders utilize the same
stud, the subsequent generation of dogs will contain many half-siblings. Since
popular sires arise in every dog generation, and the popular sires of one
generation may be the sons or nephews of those of the previous generation, the
level of inbreeding increases.
Some have argued that inbreeding depression—a complex of reproductive woes and
susceptibility to diseases—is not a real concern, pointing to laboratory mice
as an example. Strains of lab mice are highly inbred, brother to sister for
many generations, to render them homozygous virtually all traits. This makes
them very useful to researchers because the strengths and weaknesses of each
strain are well known and documented so the most useful strain can be selected
for a particular line of research.
But dogs are not laboratory mice. No dog breeder would dream of breeding
brother/sister for 20 generations or more. And just as well that they do not.
When lab mouse strains are developed at least 90% of the lines descending from
the original pair will go extinct due to the various effects of inbreeding
depression. Even those that survive are not paragons of health and soundness.
Some are deliberately maintained due to the presence of a non-lethal defect,
others might lack such defects but if cast into the mousy equivalent of the
"real world," would soon perish. Without the highly controlled
environment of the laboratory, with it’s regulated temperature, regular
wholesome food, clean water, and—from a mousy standpoint—comfortable quarters,
they could not cope.
While our dogs may have the best food and housing we can provide them, they are
still much more a part of the "real" world, with it’s exposure to
inclement weather, microbes and an assortment of other inconveniences, than is
any lab mouse. Too much inbreeding puts them at risk of succumbing to those
inconveniences.
To maintain our breeds into the next millennium, breeders need to review and
revise their priorities.
We can no longer breed for the prime purpose of producing winners in conformation.
Physical appearance alone is insufficient to gauge the overall health and
soundness of the dog. The physical and mental demands of showing are not
sufficient to separate out the marginally fit and the specialized environment
of the conformation show will not necessarily select the dog best suited to
function outside that arena.
We must put much more emphasis on health, not just he obvious things like hip
and eye clearances, but more subtle considerations. Does the dog have stamina?
Is it prone to catch every little bug that comes along? Does it have a queasy
digestive system? Is it capable of breeding without veterinary or other human
intervention? If it is a bitch, can it whelp, nurse and raise its puppies
without extraordinary efforts on the part of the breeder?
Finally, we must strive to maintain whatever genetic diversity remains in our
breeds through assortative mating, the mating of
individuals who share desirable traits while at the same time sharing as little
common ancestry as possible.
If we can do these things, our dogs may survive well into the next millennium.
If we do not, they risk extinction.
Copyright 2000 C. A. Sharp. All rights
reserved. C.A. Sharp
is editor of the "Double Helix Network News", the quarterly
newsletter for those interested in genetics and hereditary disease in the
Australian Shepherd.
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