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Purebred Dogs – Health Problems Due to Inbreeding

By Michele Welton, Dog Trainer, Breed Selection Consultant, Author of 15 Dog Books

If you're a science fiction fan, you've surely seen shows where a small population on some isolated planet has been inbreeding amongst themselves for generations. Now their DNA is degrading, accumulating more and more defects, and the people are growing weak and sick and are in desperate need of an influx of new genes to strengthen their gene pool so they don't all die off.

Those plots are based on fact.

In any population of living creatures, recombining the same genes over and over, without the regular introduction of new and unrelated genes, is a big problem. It even has a name – loss of genetic diversity  – and it results in weakness and health problems.

Loss of genetic diversity occurs in ALL populations that become too inbred, from laboratory rats to beef cattle to human beings – and unfortunately, it has already happened in purebred dogs.

Let me tell you a story.

Until the mid-1800s, people who bred dogs weren't interested in registries or pedigrees. Their breeding criteria was simple: If a farmer had a good hunting dog who was medium-sized and short-coated, and if those traits were useful in his terrain and climate, he bred it to another good hunting dog who was medium-sized and short-coated. Similar working ability and similar physical traits necessary to do the work.

That's all it took to be a good candidate for breeding. So the gene pool of dogs available for breeding was varied and diverse and dogs bred together were seldom related.

Geneticists tell us that this kind of genetic diversity is very healthy.

But this all changed in the mid-1800s, when...

...a few European dog fanciers – wealthy, socially prominent, and proud of their own pedigrees – decided that purity of bloodline should be as attended to in dogs as in people.

In their view, "common" people whose family lineages weren't recorded and documented were inferior – so too must be the case with dogs.

This small group of dog fanciers decided to start breeding separate canine races with documented lineages.

So here's what these fanciers did:

  1. First in Europe, then in the United States, they chose the FOUNDING MEMBERS for each breed and listed them in an official "Stud Book".
  2. The founding members were bred together and to their descendents, who were also bred together or bred back to the founding members. For puppies to be registered as part of the "official breed", they had to come from the founding members or from the descendents of the founding members.
  3. The Stud Book was soon closed to any new entries – a major mistake. The science of genetics was not yet understood, so these dog fanciers didn't realize the disastrous consequences of founding entire races (which they called "breeds") on such a small number of dogs and then closing the Stud Book so quickly.

Many of the health problems in purebred dogs today are a result of what geneticists call the founder's effect, where a previously large and diverse gene pool (the genes of all dogs) was suddenly reduced to a relatively few sets of genes, which were reproduced over and over, with no new genes added.

Then came World I.

The Great Depression.

World War II.

Nobody could afford to keep and breed dogs, especially large breeds that required a lot of food, during hard times. In areas that saw heavy military action, large populations of dogs were wiped out. The gene pools shrank.

As the years went on, the gene pools shrank even more because.... well, you've heard the expression: "The times, they are a'changin?"

  • For example, when fishing trawlers developed new technology, Portuguese Water Dogs were no longer needed as fishermen's helpers.
  • When mountain rescue techniques were modernized, Saint Bernards were no longer needed as Alpine rescue dogs.
  • When wolves vanished from Ireland and otter-hunting was banned in England, who needed Irish Wolfhounds or Otterhounds?

Whenever gene pools shrink, breeders who are fanatical about keeping races "pure" make do with whatever few dogs remain – inbreeding them and their descendents even more vigorously.

In some breeds, it wasn't world events that caused shrinking gene pools – it was a deliberate choice. Some breeds that came in different sizes, coats, or colors used to be bred together, no problem – until breeders decided that those dogs should not  be bred together any more. In some cases, fanciers even divided their breed into completely separate  breeds or varieties.

This is called breed fragmentation  and it means that breeders have even fewer options for choosing mates.

For example, the Belgian Shepherd comes in several colors and coat lengths that were always allowed to be interbred. Today, however, they're divided into FOUR "breeds" – the longhaired black Groenendael, the longhaired fawn Tervuren, the shorthaired fawn Malinois, and the shaggy fawn Laekenois.

Even when these varieties occur in the same litter, they're labeled separate breeds and not interbred.

The Norwich and Norfolk Terriers started out as one breed until fanciers decided they should be separate breeds based on...

...their ears. Yes. Such an important characteristic to focus on. If it had prick ears, it became a Norwich. If it had drop ears, it became a Norfolk. They're not interbred.

Great Danes come in six colors, but the national club has strict rules about which colors can be bred to which.

Thus, a breeder with a certain color of Great Dane can't choose a mate from the entire Great Dane gene pool, but only from a vastly smaller gene pool of "complementary" colors.

Dachshunds are divided into Miniature and Standard sizes. Poodles are divided into Toy, Miniature, and Standard sizes.

Any Dachshund or Poodle who happens to be in between the "official" sizes is frowned on for breeding purposes – even when their genes could contribute more variety to the gene pool.

Even when a breed has not been "officially" fragmented (officially divided into different varieties)...

Breeders often fragment their breed unofficially.

For example, breeders who produce dogs for the show ring and breeders who produce dogs for working purposes don't interbreed their two "types".

Examples include English Setters from show lines and English Setters from hunting lines; Border Collies from show lines and Border Collies from herding lines; German Shepherds from show lines and German Shepherds from protection lines.

A few breeders will blend types, but most breeders stick to one type. This, of course, means a smaller gene pool for each "type".

Show breeders may be the worst offenders

Breeders who breed dogs for dog shows are focused on producing dogs who match the Breed Standard, which includes a multitude of specific details – ears positioned just so, eyes shaped just so, color and markings just so.

But you don't maximize genetic diversity by standardizing dogs.

Standardizing means removing genes from the gene pool – any genes that have been arbitrarily deemed "not desired". Standardizing means that a small group of dog fanciers look at all the possible traits in dogs – traits that control coat, color, head shape, ear carriage, tail, etc. – and decide that only one (or a few) choices for that characteristic are acceptable.

All the other choices become "bad" and are removed from the gene pool by not breeding any dogs who happen to have those choices.

The problem is that genes don't float around loose in a dog's cells. They're physically connected to other genes. When you don't allow those choices in ANY member of the breed, then whatever other genes those genes were linked to – including good genes for health or temperament – are ALSO lost. Lost to the entire breed. And that's loss of genetic diversity.

Now, breeding to some physical standard is how breeds were developed in the first place, but once a breed has been established, maintaining general distinguishing physical features should be enough. There is no mistaking a Labrador Retriever for a Collie or a Fox Terrier. Becoming too focused on details and eliminating too many dogs as potential breeding stock results in more inbreeding – and less genetic diversity.

So...we've talked about purebred dogs being so inbred due to:

  • a small number of founding members when the breed was first begun
  • gene pools becoming smaller during wars and economic depressions
  • gene pools becoming smaller when changing times made some working breeds obsolete
  • gene pools becoming smaller when breeders fragment their breed into different "varieties" based on size, coat, or color
  • gene pools becoming smaller when breeders fragment their breed into "show types" and "working types"
  • gene pool becoming smaller when breeders won't breed any "unregistered" dogs (even when they're perfectly purebred)
  • gene pools becoming smaller when breeders eliminate too many dogs as potential breeding stock – based on picayune details

Smaller gene pools = more inbreeding

Finally, there is deliberate breeding of closely-related dogs

In the early 1900s, when Gregor Mendel developed the science of genetics, breeders were delighted to learn that if you wanted to "fix" certain traits within a breed (so that those traits would occur reliably), the quickest way to do it was to breed together dogs that were closely related.

Why does that work? Because traits are carried on genes, and relatives SHARE many of the same genes.

This was just the information breeders needed to start their practice (which continues to this day) of deliberately breeding dogs who are closely related – father to daughter, mother to son, brother to sister, grandfather to granddaughter, grandmother to grandson, uncle to niece, aunt to nephew, cousin to cousin, etc.

Inbreeding means the same ancestor is listed on BOTH sides of a pedigree – on the father's side and on the mother's side.

Inbreeding versus "Linebreeding"

Right now, all the way from my house, I can hear some breeders shouting: "Hey! It's only inbreeding if you breed parent-to-child or sibling-to-sibling! We don't inbreed! We linebreed! There's a big difference between inbreeding and linebreeding!"

Sorry, but no. There isn't.

Linebreeding is not even a real genetic term. Breeders made it up to differentiate the closest-possible breedings (parent-to-child and sibling-to-sibling) from breedings that are not quite so close (grandparent-to-grandchild, uncle-to-niece, aunt-to-nephew, and cousin-to-cousin).

"Linebreeding" sounds much better than inbreeding, so it's understandable that breeders prefer to use it.

Unfortunately, geneticists tell us that there is really no such thing.

Within the small, closed gene pools of purebred dogs, if a pedigree includes the same name on both sides, that's inbreeding.

The only question becomes:

How much  inbreeding is it?

Yes, you can actually measure the degree  of inbreeding in a dog. And you should, before you buy a purebred puppy.

We'll talk about how shortly.

Right now it's time to talk about why all this inbreeding is so bad.

HOW inbreeding leads to health problems

Your dog inherits his genes from his parents. You knew that. What you may not have realized is that for each feature of his body, he actually gets TWO genes – one from each parent. These two genes function as a pair. Each dog has 40,000 to 50,000 pairs of genes.

Just to make sure you understand how this works: Obviously, a dog can't pass along his actual GENE to his offspring. If he did, he wouldn't have it anymore himself, would he? No, dogs have copies of their genes in their sperm cells (males) and egg cells (females). These copies are what get passed along to offspring, during the mating act.

The problem is this:
Not all genes are NORMAL.
Some genes, in fact, are DEFECTIVE.

If your dog inherits a defective gene for some important organ or system of the body – such as his eyes, heart, kidneys, skin, joints, digestive system, etc. – this can cause a serious health problem.

Defective genes aren't rare. Every dog (in fact, every living creature – including every person) has some defective genes.

That's the bad news.

The good news is: genes come in PAIRS.

And Mother Nature, in her wisdom, has decreed that for most body parts, as long as ONE gene in the pair is normal, that's enough for the body part to work normally.

In other words, for most body parts, BOTH genes of a pair need to be defective in order to cause a health problem.

For example, consider a pair of genes for the retina (part of the eye). If a puppy inherits TWO defective retina genes (one from each parent), he will develop a serious eye disease called progressive retinal atrophy (PRA), which leads to blindness.

But if he inherits only ONE defective retina gene (from one parent) while the retina gene from his other parent is normal, his retinas will work fine. The normal gene, you see, is able to "cover up" the defective gene. Another way to put it is that the defective gene "hides" behind the normal gene.

A dog with a "hidden" defective gene for a particular health problem is said to CARRY that health problem.

So this puppy with only one defective retina gene is a CARRIER of progressive retinal atrophy (PRA). He won't develop the disease himself, but if he is bred someday, his offspring may inherit his normal retina gene OR his defective retina gene – it's a matter of random chance.

Now, carrying a defective gene is not a problem in a very large gene pool of unrelated dogs, because two dogs bred together would probably not be related. So they would be unlikely to carry the SAME defective gene.

But in the small gene pools of each breed,
where so many dogs ARE related,
many of their genes are the SAME –
including defective genes.

That means the risk is greatly increased
that two dogs of the same breed
DO have the same defective gene.

So when they breed together,
both of those defective genes will "come together"
as a defective PAIR in their puppies,
and those puppies will have the health problem.

So now you see the problem with inbreeding –
when related dogs are bred together,
defective genes are more likely to "match up".

You might be wondering.....

"Could you breed related dogs if you just made sure that they didn't carry the same defective genes?"

Yes, but unfortunately you can't tell by looking at a dog whether both of his genes for any given trait are normal – or whether one is normal and one is defective. Only by looking into a dog's DNA would you be able to see a defective gene.

happy faceThe good news is: DNA testing does exist.

You probably know a little about DNA testing from watching crime shows like CSI. From a small sample of your dog's blood or from saliva swabbed from his mouth, a testing laboratory can examine your dog's DNA. A DNA test for a specific health problem can tell you...

  • whether your dog has inherited two defective genes for that health problem and will thus develop it as he matures
  • whether he carries one defective gene for that health problem, so he will not develop it himself but he could pass it along to his offspring if you bred him
  • or whether he has inherited NO defective genes for that health problem and can neither develop it nor pass it along to offspring

sad faceThe bad news is: DNA testing is available ONLY for a few breeds – and ONLY for a few health problems.

DNA testing is breed-specific and disease-specific. That means you can't examine the DNA of just any dog for just any disease. Researchers spend years studying a specific set of genes for a specific breed, looking for the specific gene markers for a specific disease. Breed clubs have to raise tons of money so they can pay researchers to study their particular breed.

At this point in time, DNA tests have been developed for only a few health problems in a few breeds. For example:

  • A DNA test can detect the eye disease PRA in Toy Poodles.
  • A DNA test can detect the neurological disease GCL in Cairn Terriers.
  • A DNA test can detect the blood-clotting disease vWD in Shelties.
  • A DNA test can detect the kidney disease renal dysplasia in Lhasa Apsos.

But for the vast majority of breeds, and the vast majority of health problems, no DNA tests exist yet.

For those breeds and those health problems, you have to use conventional medical tests like X-rays, blood tests, eye exams, and cardiac ultrasounds. These tests can show whether a dog HAS the health problem. But what these tests don't show are hidden defective genes – so you can't tell whether your dog CARRIES a gene for a health problem and could thus pass it along to his offspring.

And that means...

That until we have sophisticated DNA tests that can pinpoint every hidden defective gene (so we know WHICH defective genes each dog has and therefore WHO can safely be bred to WHOM)...

...the best chance of breeding dogs who don't have the SAME defective genes is to breed UNRELATED dogs.

Inbreeding Depression

Now, it's bad enough when defective genes that match up are MAJOR genes like the ones responsible for PRA. When the retinas of the eyes fail, the result is obvious and dramatic – the dog is blind.

But many defective genes are MINOR genes. A minor gene is responsible for a very tiny little part of some organ or bodily system. When a minor gene is defective, the organ or bodily system doesn't fail outright – it just works a little bit LESS WELL. Say, 5% less well, or 10% less well.

This might be barely noticeable at first. But as a family of dogs becomes more and more inbred, more and more of these minor genes match up and accumulate, and functionality becomes more and more diminished.

It's a slow-developing condition, but it's very real – and it occurs in all populations of inbred living creatures, whether laboratory mice, beef cattle, human beings, or purebred dogs. This insidious condition is called inbreeding depression.

Inbreeding depression is a slow accumulation of defective genes and it results in:

  • a shorter lifespan
  • a weaker immune system
  • chronic infections
  • fertility and reproductive problems
  • mental and behavioral abnormalities such as shyness, aggression, or a high-strung temperament

Today, increasing numbers of purebred dogs are afflicted with immune system diseases, chronic skin and ear infections, a high-strung temperament, unwarranted aggression or shyness, unwillingness to mate, failure to conceive, inability to birth puppies, smaller litters, increased number of stillborn or weak puppies, and poor mothering skills.

Most alarmingly, breeds that used to live 14-18 years are now lucky to reach 8-12.

In her article, The Downside of Inbreeding: It's Time For a New Approach, C.A. Sharp, an expert on canine genetics and hereditary diseases, says:

"In recent years, purebred dogs have experienced increasing problems with hereditary diseases and defects. The causes are complex, including genetic load, defective genes, genetic bottlenecks, closed gene pools, gene pool fragmentation, and genetic drift, but all are attributable to inbreeding."

In Breeding Dogs For The Next Millennium, Hellmuth Wachtel, Ph.D., says:

"Inbreeding was once a valuable tool in shaping today's breeds [but] it has turned into a fatal and disastrous habit."

Dr. John Armstrong Ph.D., noted professor of biology and genetics, says:

"Our breeds are becoming progressively more inbred. My observation is that most are on the road to extinction, but most breeders do not even realize it."

Inbreeding can be measured

If a dog has a written pedigree, there's a mathematical formula called Wright's Coefficient of Inbreeding that can measure the dog's level of inbreeding.

Because it's a very complex formula, it's calculated on a computer, using a pedigree software program such as CompuPed or BreedMate. Every breeder should be doing this for every litter – unfortunately, almost no breeder IS.

When the formula is run, it reports a dog's coefficient of inbreeding (COI). The COI tells you, based on how many common ancestors the dog has and where they're located in his pedigree, what percentage of his genes are likely to be the SAME. The more genes that are the same, the greater the risk that some of them will be matching defective genes.

To be sure you're getting a valid COI, the pedigree needs to include more than 6 generations. How many more is debated by geneticists and statisticians, but for most breeds, running the formula on 8-10 generations is an accurate look at the degree of inbreeding.

"What does a COI look like? Is it a number?"

Yes, it's usually expressed as a percentage. For example, 5% or 12.5%.

A low COI (up to about 5%) means that the dog doesn't have many common ancestors (names who appear on both sides of his family). So the percentage of his genes that are likely to be the same is very low, giving him the best chance of avoiding defective genes matching up.

Geneticist Dr. John Armstrong says that in his breed, Standard Poodles, a dog with a COI of 5% will live, on average, about 3 years longer than a dog with a COI of 35%.

Here's the really bad news:

The typical COI of many breeds (especially in show lines) is 12-14%, with many dogs at 20-40% and some even higher than that.

Now, remember those breeders who shouted that they were NOT inbreeding?

Well, genetically speaking, a COI of 12.5% is the same as if the breeder had done a grandparent-to-grandchild breeding, and a COI of 25% is the same as a parent-to-child or brother-to-sister breeding.

So breeders who declare emphatically that they would never do such close breedings (because THAT would be inbreeding) are producing dogs with the same degree of inbreeding... only they're calling those dogs linebred.

Most breeders (and most prospective owners) simply have no idea how dangerously high the levels of inbreeding have become in purebred dogs.

With COIs being so high in purebred dogs, and with high COIs clearly connected to health problems, you should be able to ask any breeder, "What is the coefficient of inbreeding for this puppy?" and he should be able to tell you.

Unfortunately, that isn't the case. Not even close.

  • 99% of the people offering purebred puppies to the public cannot tell you their COI. That's appalling.
  • In fact, 99% of the people offering purebred puppies to the public have never even HEARD of a COI.
  • Most of them have never even LOOKED at their dogs' pedigrees beyond 3 or 4 or maybe 5 generations.
  • And that means they have no idea how inbred their puppies really are.

And my friends,
THAT ignorance by breeders
is one of the major reasons
that purebred dogs are so inbred –
and so unhealthy.

Michele Welton with BuffyAbout the author: Michele Welton has over 40 years of experience as a Dog Trainer, Dog Breed Consultant, and founder of three Dog Training Centers. An expert researcher and author of 15 books about dogs, she loves helping people choose, train, and care for their dogs.

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