The Price of
Popularity:
Popular Sires and Population Genetics |
Consider the hypothetical case of Old Blue, Malthound
extraordinaire. Blue was perfect: Sound, healthy and smart. On week days
he retrieved malt balls from dawn to dusk. On weekends he sparkled in malt
field and obedience trials as well as conformation shows, where he baited
to--you guessed it--malt balls.
Everybody had a good reason to breed to Blue, so
everybody did. His descendants trotted in his paw-prints on down through
their generations. Blue died full of years and full of honor. But what
people didn't know was that Old Blue, good as he was, carried a few bad
genes. They didn't affect him, nor the vast majority of his immediate
descendants. To complicate the matter further, some of those bad genes
were linked to genes for important Malthound traits.
A few Malthounds with problems started showing up. They
seemed isolated, so everyone assumed it was "just one of those things." A
few declared them "no big deal." Those individuals usually had affected
dogs. All in all, folks carried on as usual.
Time passed. More problem dogs turned up. People made a
point not to mention the problems to others because everyone knows the
stud owner always blames the bitch for the bad tings and takes credit for
the good. Stud owners knew it best to keep quiet so as not to borrow
trouble. Overall, nobody did anything to get to the bottom of the
problems, because if they were really significant, everybody would be
talking about it, right?
Years passed. Old Blue had long since moldered in his
grave. By now, everyone was having problems, from big ones like cataracts,
epilepsy or thyroid disease to less specific things like poor-keepers,
lack of mothering ability and short life-span. "Where can I go to get away
from this?" breeders wondered. The answer was nowhere.
People became angry. "The responsible parties should be
punished!" Breeders who felt their programs might be implicated
stonewalled. Some quietly decided to shoot, shovel and shut-up. A few
brave souls stood up and admitted their dogs had a problem and were
hounded out of the breed.
The war raged on, with owners, breeders and rescue
workers flinging accusations at each other. Meanwhile everybody carried on
as always. After another decade or two the entire Malthound breed
collapsed under the weight of its accumulated genetic debris and went
extinct.
This drastic little fable is an exaggeration--but not
much of one. Here's similar, though less drastic, example from real life:
There once was a Quarter Horse stallion named Impressive. The name fit. He
sired many foals who also exhibited his desired traits. But when they and
their descendants were bred to each other, those offspring sometimes died.
Impressive had been the carrier of a lethal single-gene recessive trait.
No one knew it was there until they started in-breeding on him. The
situation of a single sire having this kind of drastic genetic effect on a
breed became known as the "Impressive Syndrome."
Many species and breeds of domestic animals, including
dogs, have suffered "Impressive Syndromes" of their own. But cases like
that of Impressive are only the tip of the iceberg. A single-gene
recessive becomes obvious in just a few generations. But what about more
complex traits?
This is not to say that those popular sires we so
admire are bad breeding prospects. Their many excellent traits should be
utilized, but even the best of them has genes for negative traits.
The problem is not the popular sires, but how we use
them. For a century or more, in-breeding has been the name of the game.
(For the purposes of this article, "in-breeding" refers to the breeding of
dogs related to each other and therefore includes line-breeding.) By
breeding related individuals, a breeder increased his odds of producing
dogs homozygous for the traits he wanted. Homozygous individuals are much
more likely to produce those traits in the next generation.
When a male exhibits a number of positive traits and
then proves his ability to produce those traits he may become a popular
sire, one that is used by almost everyone breeding during his lifetime,
and maybe beyond, thanks to frozen semen.
Since the offspring and grand-offspring and so on are
good, breeders start breeding them to each other. If the results continue
to be good, additional back-crosses may be made for generations. Sometimes
a sire will be so heavily used that, decades hence, breeders may not even
be aware of how closely bred their animals are because the dog no longer
appears on their pedigrees.
This is the case in Australian Shepherds. Most
show-line Aussies trace back, repeatedly, to one or both of two full
brothers: Wildhagen's Dutchman of Flintridge and
Fieldmaster of Flintridge. These, products of a program of
inbreeding, were quality individuals and top-producing sires. They are
largely responsible for the over-all quality and uniformity we see in the
breed ring today--a uniformity that did not exist before their birth
nearly three decades ago.
Working lines have also seen prominent sires, but
performance traits are far more complex, genetically and because of the
significant impact of environment. They are therefore harder to fix.
Performance breeders will in-breed, but are more likely to stress
behavioral traits and general soundness than pedigree and conformational
minutiae. The best working sires rarely become as ubiquitous as the best
show-line sires.
Not every popular sire becomes so because of his
ability to produce quality offspring. Some have won major events or are
owned by individuals with a knack for promotion. Such dogs may prove to be
wash-outs once their get is old enough to evaluate. But a lot of breeders
have been using the animal for the few years it takes to figure that out,
the damage may already have been done.
Use of even the best popular sires, by its very nature,
limits the frequency of some genes in the breed gene pool while
simultaneously increasing the frequency of others. Since sons and
grandsons of popular sires tend to become popular sires the trend
continues, resulting in further decrease and even extinction of some genes
while others become homozygous throughout the breed. Some of these traits
will be positive, but not all of them.
The owners of Old Blue, the Malthound in the opening
fable, and those who owned his most immediate descendants had no idea what
was happening under their noses. They were delighted to have superior
studs and even more delighted to breed them to as many good bitches as
possible.
Dog breeding and promoting is an expensive proposition.
One usually winds up in the hole. But owning a popular sire can change
that. The situation looks like a winner for everyone--the stud owner finds
his financial burden reduced while breeders far and wide get to partake of
his dog's golden genes.
No one breeding dogs wants to produce sick dogs. A
small minority are callous and short-sighted enough to shrug genetic
problems off as the price you pay to get winners, but even they do their
best to avoid letting it come to general attention.
We need a total re-thinking of how we utilize stud
animals. No single dog, no matter how superior, should dominate the gene
pool of its breed. Owners of such sires should give serious consideration
to limiting how often that dog is used, annually, through its lifetime and
on into the future, if frozen semen is stored. The stud owner should also
look not only at the quality of the bitches being presented, but their
pedigrees. How much will the level of inbreeding be increased by a
particular mating?
The bitch owner also needs to think twice about popular
sires. If you breed to the stud of the moment and everyone else is doing
the same, where will you go when it comes time to make an outcross?
Finally, the attitude toward genetic disease itself has
to change. It must cease being everyone's dirty little secret. It must
cease being a brick with which we bludgeon those with the honesty to admit
it happened to them. It must become a topic of open, reasoned discussion
so owner of stud and bitch alike can make informed breeding decisions.
Unless breeders and owners re-think their long-term goals and how they
react to hereditary problems, the situation will only get worse.
C.A. Sharp is editor of the "Double Helix Network
News". This article appeared in Vol. IV, No. 3 (Summer 1998). It may be
reprinted providing it is not altered and appropriate credit is given.
August 18, 1998
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