Tag Archives: genes

Death by a Thousand Health Tests

Food for thought is always a good thing, at least in my world, it keeps my mind open to new ideas. As I’ve aged I’ve found it’s ever more important not to get stuck in my ways and thinking about what other people have to say on a topic keeps me out of ruts.  So when I read the article I’m sharing with you today about health testing, I found myself thinking. Now, a word of warning, some of my close friends would tell you, “Sally’s thinking takes some rather weird detours now and again, so when she says “I was thinking” you might wanna run for cover!”

We all talk about being a responsible breeder, and of course, we consider a part of that responsibility to be health testing of the parents. Now mind you, I’m getting to that place where I’m almost old as dirt, so I’m one of those breeders who started in the game long before the majority of the health tests of today were available. While I’m all for health testing to gain knowledge of what is in the genes I’m about to mix together, I’m also one of those breeders who will tell you to use a good ole dose of common sense when breeding. While I’d never throw health testing to the side, I am also realizing that as the population of Gordon Setters declines, so follows our number of breeding options. This is a big conundrum we face folks, and it will take dedication, smart decisions and some good old common sense to preserve the best of our breed.

Sally Gift, AZ              Photograph by Susan Roy Nelson, WY

With that said, I don’t know as I agree with everything in this article, but I do know it will give you some food for thought so I’m sharing, for your reading and thinking pleasure.  If you’d like to share your thoughts after reading this feel free to use the comment section!

Breeder On The Edge

Death From a Thousand Health Tests by Amanda Kelly

AUTHOR:  A dedicated hobby breeder in a terminally rare breed, Amanda Kelly perpetually finds herself on the edge of everything from ecstasy to bankruptcy, quitting and insanity.

I had a really interesting conversation with a geneticist the other day that got me thinking: science is offering us more and more great ways to evaluate the health of our dogs…but when does enough turn into too much? When do we cross the threshold from helpful information to complete paralysis? Or outright bankruptcy? How do we avoid both?

Prioritization
The test we were discussing is quite a new one in my breed (Toy Manchester Terriers). It is for a condition called Xanthinuria that causes dogs to form a very rare form of kidney stone. There have only been three clinically affected dogs that I am aware of (full disclosure: we bred one). After encountering the issue, a fellow breeder did a little digging and discovered that a marker associated with the condition in humans worked for our breed as well. Kudos to her for being proactive and finding out more! The American and Canadian breed clubs helped proof the test and voila, it is now available commercially at quite a reasonable cost.

When I looked at dogs in my own breeding program that came up as carriers however, I was surprised as I would have expected more of our puppies to have or be forming stones than was the case.  So, what does that say about the disease? Do all affected puppies form stones? If not, what is the rate?  I found the answers to those Qs simultaneously helpful and troubling.

Apparently, current thinking is that approximately 50% of males with two copies of the mutation form stones or have associated kidney issues, while very few females with the same status have a problem (likely because they do a better job of emptying their bladders). Now, these are just rough estimates because the disease as a whole is rare and hasn’t been extensively studied, but it does raise an important question: what are we as breeders to do with this information and associated results of the genetic test?

The Jigsaw
The simple fact is that the more tests we have, the more pieces of info we have to try and reconcile when planning a breeding. At present, Toy Manchester breeders as a group are variously clearing things like hips, patellas, eyes, thyroid, and hearts plus DNA testing for von Willebrand’s Disease, and, now, potentially xanthinuria. That’s 7 tests, some with questionable value based on anecdotal and surveillance evidence, if we’re being honest. We’re also actively working to identify a test for juvenile cardiomyopathy.

The end result of all of that testing is a ton of information, which is great from the perspective of evaluating the health of individual dogs but also creates a number of very real problems for breeders in areas like liability, reputation and cost.

In the past, these factors were certainly in play but their effects were somewhat muted. Breeders worked for years to learn about their breed and their lines so they could make informed decisions and minimize the risk of producing issues. Health tests initially concentrated on measuring phenotype as an indicator and we worked with what we had. The important thing was that we could confidently tell puppy buyers we had done everything possible to produce healthy, happy puppies and if a problem appeared we were solid in the knowledge we had used all available tools to their best advantage.

Enter the genetic test. In my breed, the first one was for von Willebrand’s Disease (a blood clotting disorder). For years this disease was monitored by assay testing that measured the actual amount of the specific type of clotting factor in the blood and projected genetic status based on corresponding ranges. It was a pain to do but everyone muddled through as it was one of the few standard health tests most breeders did in the 1980s and 90s. When the genetic marker was identified, some breeders lost their ever loving minds. Dozens of valuable dogs were promptly spayed and neutered while breeders across North America began making pronunciations about “never” breeding a carrier even to a clear.

There’s no question, needless damage was done to the gene pool — especially when you consider there had never been a documented case of a Manchester actually bleeding out because it was vWD affected (at least not one I am aware of). Eventually breeders learned how to work with the DNA results and things calmed down. Our new test allowed us to easily avoid producing “affected” puppies (i.e., a dog with two copies of the gene, not necessarily clinically affected) and, regardless of the actual effects of the condition itself, doing so quickly became “right” and “just”.  It was an approach we ourselves endorsed and followed because, after all, “responsible breeders” test.

And thus, the line in the sand was drawn. It’s a line we in the dog community drew ourselves and it’s one most of us dare not cross.

Unlimited Liability
The scientific advancements that brought us more genetic tests took place against an active backdrop that included the rise of animal rights, increasing anthropomorphization of pets, emergence of puppy lemon laws, and the advent of social media. Now, it may seem odd to bring those factors into a discussion of genetic testing, but they each play a very important role in describing the environment within which we are working. An environment that values reputation above all else and that pits breeding decisions against financial liability in a way many breeders don’t consider.

Any breeder with two licks of sense knows that when it comes to breeding dogs, the most important possession you have — more important than any ribbon you may ever win — is your reputation. Your reputation affects everything you do, from access to stud dogs and puppies to demand for same. In a subjective sport like ours, it can even affect your ability to succeed in the show ring.

Protecting, fostering and growing a reputation can become all-consuming. Let’s cut to the chase here: We’re operating in an environment that can make a competition out of anything — which is why sometimes reputation management, and by extension health testing, becomes as much about one upmanship and moral superiority as it is the well-being of the dogs in question. That probably explains why many of the tests done in my breed are done by rote…because they are available, not because we have objectively identified a need for them. Not because we have established that rates of thyroid problems or eye issues, for example, are any higher in our breed than in the general dog population. No, we do them because we can and because we feel (tell one another?) that we should. And why is that? It’s because we have established as fact within our community that good breeders test and bad breeders don’t. So, we all work extra hard to make sure our conduct is above reproach.

That core belief is just as strong outside of the dog community, where we have worked hard to battle animal rights messaging by establishing health testing as a key feature differentiating responsible breeders from backyard breeders. And it’s a great message — easy to understand and easy for the public to actively measure when they are talking to breeders. The trouble is, that message comes pre-loaded with expectations we can never live up to. Expectations that if you buy from a good breeder your dog will never ever have health issues. That health tested parents won’t produce problems. That responsible breeders can be God.

And therein lies the problem. The more health testing we do, the bigger the gap grows between public expectations and the reality of what we can deliver…and with it, our financial liability. Because hey, don’t forget, in addition to health testing, responsible breeders also guarantee their puppies. Whether through provision of a replacement puppy or return of purchase funds, those guarantees do carry financial risk and can’t be dismissed at the best of times and even less so as puppy lemon laws increasingly make puppy health a legal matter. So, tell me…how do you think small claims court would view a breeder that knowingly produces a problem? Or one that unknowingly produces one because they failed to use the tests available? It’s a perfect catch 22 in the making.

Risk Reduction
It’s a simple axiom that the more health testing available, the less we talk about what we’re trying to avoid producing and the more we talk about what we are willing to risk producing. There isn’t a perfect dog out there and every biological organism possesses deleterious genes for something, regardless of whether we can test for it or not.  The more tests available, the more complicated planning breedings becomes because we all naturally want to avoid the chances of producing any problem at all.  But is that a realistic goal?

What did I say we were up to in my breed – seven tests? Eight? Heck, even I lose track sometimes. And all of these tests in an era when the number of puppies being produced continues to drop at an alarming rate. Under 200 Toy and Standard Manchester Terriers “combined” were produced in North America last year, so I’m sure you can image how difficult it might be to match test results for potential breedings (particularly if we’re testing for everything under the sun). Or what the costs of doing those breedings might be as we look further and further afield, let alone the relative cost of doing the health screening to begin with in a breed with relatively small litter sizes and low purchase prices. The financials would rock your world and have you questioning my sanity, so we won’t go there other than to say red is a better quality in a new coat than a ledger (but I digress…).

I asked a few researchers and vets what they felt breeders should do with test results when there are many to consider.  The consistent response was that we need to prioritize — and that’s a completely reasonable thing for a scientist to say…and a very difficult thing for a devoted dog breeder to actually do.

Never mind the costs, appearance or liability — I genuinely don’t want to be responsible through conscious decision for producing a sick puppy. It is one thing to employ testing, tools and techniques to theoretically reduce disease and quite another to look at a plethora of results and say “This one I can live with.”

And what happens once the die is cast?  If we use Xanthinuria as an example, I could choose to breed two carriers together and test all of the puppies…but then what? Sure, knowing a puppy has two copies of the gene and is at higher risk of forming stones will be helpful to an owner who could keep the dog on a low purine diet and perhaps avoid issues altogether…but could I sell a puppy like that? For how much? Would anyone take it if I was giving it away? What level of financial responsibility do I hold if it does develop an issue two, five or 10 years down the road? What if there are multiple puppies with two copies of the gene in the litter?

And that, ladies and gentlemen, is the ethical dilemma of the future.  Perhaps we in smaller, rarer breeds are dealing with it sooner, but it is a dilemma I truly believe every breed and breeder will face at some point.  It has the potential to be absolutely paralyzing as we seek to do the right thing in a world where that is increasingly less black and white than it seemed a few short years ago.

I don’t know exactly how we can or should approach it — perhaps I’m hoping you’ll be able to tell me. I suspect that monitoring of actual breed health through health surveys and breeders sharing information on what they are seeing will be increasingly important if we wish to prioritize according to real information. And I do know that one of the things we absolutely must do is change how we discuss health testing. The way we talk about each other (oh Lordy, put a star next to that one!) and to each other as well as how we portray ourselves to the public. Just as important, we have to think about health tests and results holistically in the context of our breed and gene pool. In our rush to erase problems through testing, we are shown again and again that the devil we don’t know is often worse than the devil we can test for.

What To Do?
This article isn’t intended to form the cornerstone of a campaign against health testing. Far from it. I truly believe we need to use the tools available to us, particularly if they are able to help us avoid devastating issues facing our dogs and puppies. In fact, I and others in my breed have worked hard for more than a decade to see a genetic test developed for juvenile cardiomyopathy because it is a brutal, deadly disease and I want all of us to have a tool that will allow us to make informed choices and stop guessing at how to avoid it.

But I’m also a realist. Health management is a tough nut to crack even for trained geneticists let alone the average breeder doing their best to navigate an increasingly complex and technical landscape. Giving us the test results is the easy part, it seems — figuring out what to do with them is our next great challenge.

The Ins and Outs of Pedigree Analysis

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(This article is reprinted with permission of the Jerold M Bell DVM

IT’S ALL IN THE GENES

As dog breeders, we engage in genetic “experiments” each time we plan a mating. The type of mating selected should coincide with your goals. To some breeders, determining which traits will appear in the offspring of a mating is like rolling the dice – a combination of luck and chance. For others, producing certain traits involves more skill than luck – the result of careful study and planning. As breeders, we must understand how we manipulate genes within our breeding stock to produce the kinds of dogs we want. We have to first understand dogs as a species, then dogs as genetic individuals.

The species, Canis familiaris, includes all breeds of the domestic dog. Although we can argue that there is little similarity between a Chihuahua and a Saint Bernard, or that established breeds are separate entities among themselves, they all are genetically the same species. While a mating within a breed may be considered outbred, it still must be viewed as part of the whole genetic picture: a mating within an isolated, closely related, interbred population. Each breed was developed by close breeding and inbreeding among a small group of founding canine ancestors, either through a long period of genetic selection or by intensely inbreeding a smaller number of generations. The process established the breed’s characteristics and made the dogs in it breed true.

When evaluating your breeding program, remember that most traits you’re seeking cannot be changed, fixed or created in a single generation. The more information you can obtain on how certain traits have been transmitted by your dog’s ancestors, the better you can prioritize your breeding goals. Tens of thousands of genes interact to produce a single dog. All genes are inherited in pairs, one pair from the father and one from the mother. If the pair of inherited genes from both parents is identical, the pair is called homozygous. If the genes in the pair are not alike, the pair is called heterozygous. Fortunately, the gene pairs that make a dog a dog and not a cat are always homozygous. Similarly, the gene pairs that make a certain breed always breed true are also homozygous. Therefore, a large proportion of homozygous non-variable pairs – those that give a breed its specific standard – exist within each breed. It is the variable gene pairs, like those that control color, size and angulation, that produce variations within a breed.

BREEDING BY PEDIGREE

Outbreeding brings together two dogs less related than the average for the breed. This promotes more heterozygosity, and gene diversity within each dog by matching pairs of unrelated genes from different ancestors. Outbreeding can also mask the expression of recessive genes, and allow their propagation in the carrier state.

Most outbreeding tends to produce more variation within a litter. An exception would be if the parents are so dissimilar that they create a uniformity of heterozygosity. This is what usually occurs in a mismating between two breeds. The resultant litter tends to be uniform, but demonstrates “half-way points” between the dissimilar traits of the parents. Such litters may be phenotypically uniform, but will rarely breed true due to the mix of dissimilar genes.

A reason to outbreed would be to bring in new traits that your breeding stock does not possess. While the parents may be genetically dissimilar, you should choose a mate that corrects your dog’s faults but phenotypically complements your dog’s good traits.

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It is not unusual to produce an excellent quality dog from an outbred litter. The abundance of genetic variability can place all the right pieces in one individual. Many top-winning show dogs are outbred. Consequently, however, they may have low inbreeding coefficients and may lack the ability to uniformly pass on their good traits to their offspring. After an outbreeding, breeders may want to breed back to dogs related to their original stock, to increase homozygosity and attempt to solidify newly acquired traits.

Linebreeding attempts to concentrate the genes of a specific ancestor or ancestors through their appearance multiple times in a pedigree. The ancestor should appear behind more than one offspring. If an ancestor always appears behind the same offspring, you are only linebreeding on the approximately 50 percent of the genes passed to the offspring and not the ancestor itself.

It is better for linebred ancestors to appear on both the sire’s and the dam’s sides of the pedigree. That way their genes have a better chance of pairing back up in the resultant pups. Genes from common ancestors have a greater chance of expression when paired with each other than when paired with genes from other individuals, which may mask or alter their effects.

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A linebreeding may produce a puppy with magnificent qualities, but if those qualities are not present in any of the ancestors the pup has been linebred on, it may not breed true. Therefore, careful selection of mates is important, but careful selection of puppies from the resultant litter is also important to fulfill your genetic goals. Without this, you are reducing your chances of concentrating the genes of the linebred ancestor.

Increasing an individual’s homozygosity through linebreeding may not, however, reproduce an outbred ancestor. If an ancestor is outbred and generally heterozygous (Aa), increasing homozygosity will produce more AA and aa. The way to reproduce an outbred ancestor is to mate two individuals that mimic the appearance and pedigree of the ancestor’s parents.

Inbreeding significantly increases homozygosity, and therefore uniformity in litters. Inbreeding can increase the expression of both beneficial and detrimental recessive genes through pairing up. If a recessive gene (a) is rare in the population, it will almost always be masked by a dominant gene (A). Through inbreeding, a rare recessive gene (a) can be passed from a heterozygous (Aa) common ancestor through both the sire and dam, creating a homozygous recessive (aa) offspring. Inbreeding does not create undesirable genes, it simply increases the expression of those that are already present in a heterozygous state.

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Inbreeding can exacerbate a tendency toward disorders controlled by multiple genes, such as hip dysplasia and congenital heart anomalies. Unless you have prior knowledge of what milder linebreedings on the common ancestors have produced, inbreeding may expose your puppies (and puppy buyers) to extraordinary risk of genetic defects. Research has shown that inbreeding depression, or diminished health and viability through inbreeding is directly related to the amount of detrimental recessive genes present. Some lines thrive with inbreeding, and some do not.

PEDIGREE ANALYSIS

Geneticists’ and breeders’ definitions of inbreeding vary. A geneticist views inbreeding as a measurable number that goes up whenever there is a common ancestor between the sire’s and dam’s sides of the pedigree; a breeder considers inbreeding to be close inbreeding, such as father-to-daughter or brother-to-sister matings. A common ancestor, even in the eighth generation, will increase the measurable amount of inbreeding in the pedigree.

The Inbreeding Coefficient (or Wright’s coefficient) is an estimate of the percentage of all the variable gene pairs that are homozygous due to inheritance from common ancestors. It is also the average chance that any single gene pair is homozygous due to inheritance from a common ancestor. In order to determine whether a particular mating is an outbreeding or inbreeding relative to your breed, you must determine the breed’s average inbreeding coefficient. The average inbreeding coefficient of a breed will vary depending on the breed’s popularity or the age of its breeding population. A mating with an inbreeding coefficient of 14 percent based on a ten generation pedigree, would be considered moderate inbreeding for a Labrador Retriever (a popular breed with a low average inbreeding coefficient), but would be considered outbred for an Irish Water Spaniel (a rare breed with a higher average inbreeding coefficient).

For the calculated inbreeding coefficient of a pedigree to be accurate, it must be based on several generations. Inbreeding in the fifth and later generations (background inbreeding) often has a profound effect on the genetic makeup of the offspring represented by the pedigree. In studies conducted on dog breeds, the difference in inbreeding coefficients based on four versus eight generation pedigrees varied immensely. A four generation pedigree containing 28 unique ancestors for 30 positions in the pedigree could generate a low inbreeding coefficient, while eight generations of the same pedigree, which contained 212 unique ancestors out of 510 possible positions, had a considerably higher inbreeding coefficient. What seemed like an outbred mix of genes in a couple of generations, appeared as a linebred concentration of genes from influential ancestors in extended generations.

The process of calculating coefficients is too complex to present here. Several books that include how to compute coefficients are indicated at the end of this article; some computerized canine pedigree programs also compute coefficients. The analyses in this article were performed using CompuPed, by RCI Software.

[RCI Note: CompuPed computes Wright’s Inbreeding Coefficient faster and more accurately than any other PC program available. ]

Pedigree of: “Laurel Hill Braxfield Bilye”

( a spayed female Gordon Setter owned by Dr. Jerold and Mrs. Candice Bell, and co-bred by Mary Poos and Laura Bedford.)

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To visualize some of these concepts, please refer to the above pedigree. Linebred ancestors in this pedigree are in color, to help visualize their contribution. The paternal grandsire, CH Loch Adair Foxfire, and the maternal grandam, CH Loch Adair Firefly WD, are full siblings, making this a first-cousin mating. The inbreeding coefficient for a first cousin mating is 6.25%, which is considered a mild level of inbreeding. Lists of inbreeding coefficients based on different types of matings are shown in the table below.

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In Bilye’s pedigree, an inbreeding coefficient based on four generations computes to 7.81%. This is not significantly different from the estimate based on the first-cousin mating alone. Inbreeding coefficients based on increasing numbers of generations are as follows: five generations, 13.34%; six generations, 18.19%; seven generations, 22.78%; eight generations, 24.01%; ten generations, 28.63%; and twelve generations, 30.81%. The inbreeding coefficient of 30.81 percent is more than what you would find in a parent-to-offspring mating (25%). As you can see, the background inbreeding has far more influence on the total inbreeding coefficient than the first-cousin mating, which only appears to be its strongest influence.

Knowledge of the degree of inbreeding in a pedigree does not necessarily help you unless you know whose genes are being concentrated. The percent blood coefficient measures the relatedness between an ancestor and the individual represented by the pedigree. It estimates the probable percentage of genes passed down from a common ancestor. We know that a parent passes on an average of 50% of its genes, while a grandparent passes on 25%, a great-grandparent 12.5%, and so on. For every time the ancestor appears in the pedigree, its percentage of passed-on genes can be added up and its “percentage of blood” estimated.

In many breeds, an influential individual may not appear until later generations, but then will appear so many times that it necessarily contributes a large proportion of genes to the pedigree. This can occur in breeds, due to either prolific ancestors (usually stud dogs), or with a small population of dogs originating the breed. Based on a twenty-five generation pedigree of Bilye, there are only 852 unique ancestors who appear a total of over twenty-million times.

Pedigree Analysis of Laurel Hill Braxfield Bilye
(computed to 25 generations)

1st Generation

Linebred Ancesters

Percentage of blood

Appearance in pedigree

# times in pedigree

CH Afternod Drambuie 33.20% 6 33
CH Afternod Sue 27.05% 7 61
CH Afternod Callant 26.56% 5 13
“Grand-Parents” 25.00% 2 1
CH Sutherland Gallant 25.00% 3 2
CH Sutherland MacDuff 25.00% 3 3
CH Sutherland Lass of Shambray 25.00% 3 2
CH Wilson’s Corrie, CD 22.30% 7 200
CH Afternod Buchanon 20.22% 7 48
Loch Adair Diana of Redchic 17.97% 5 12
CH EEG’s Scotia Nodrog Rettes 17.76% 8 181
Afternod Ember of Gordon Hill 17.14% 8 76
CH Afternod Hickory 16.21% 6 27
CH Black Rogue of Serlway 15.72% 9 480
CH Afternod Woodbine 14.45% 6 15
CH Fast’s Falcon of Windy Hill 13.82% 8 66
Afternod Fidemac 13.67% 5 7
CH Page’s MacDonegal II 13.43% 7 56
Afternod Hedera 13.38% 7 56
CH Downside Bonnie of Serlway 12.90% 10 708
Peter of Crombie 12.76% 11 3,887
“Great-Grand-Parents” 12.50% 3 1
CH Afternod Amber 12.50% 5 5
Ben of Crombie 11.83% 11 7,584
Stylish William 11.18% 13 23,764
Stylish Billie 11.08% 14 70,542
Stylish Ranger 10.80% 15 297,331
CH Afternod Kate 10.74% 6 17
Heather Grouse 10.61% 16 1,129,656
Afternod Hedemac 10.45% 7 28

The above analysis shows the ancestral contribution of the linebred ancestors in Bilye’s pedigree. Those dogs in color were present in the five-generation pedigree. CH Afternod Drambuie has the highest genetic contribution of all of the linebred ancestors. He appears 33 times between the sixth and eighth generations. One appearance in the sixth generation contributes 1.56% of the genes to the pedigree. His total contribution is 33.2% of Bilye’s genes, second only to the parents. Therefore, in this pedigree, the most influential ancestor doesn’t even appear in the five-generation pedigree. His dam, CH Afternod Sue, appears 61 times between the seventh and tenth generations, and contributes more genes to the pedigree than a grandparent.

Foundation dogs that formed the Gordon Setter breed also play a great role in the genetic makeup of today’s dogs. Heather Grouse appears over one million times between the sixteenth and twenty-fifth generations, and almost doubles those appearances beyond the twenty-fifth generation. He contributes over ten percent of the genes to Bilye’s pedigree. This example shows that the depth of the pedigree is very important in estimating the genetic makeup of an individual. Any detrimental recessive genes carried by Heather Grouse or other founding dogs, would be expected to be widespread in the breed.

BREEDING BY APPEARANCE

Many breeders plan matings solely on the appearance of a dog and not on its pedigree or the relatedness of the prospective parents. This is called assortative mating. Breeders use positive assortative matings (like-to-like) to solidify traits, and negative assortative matings (like-to-unlike) when they wish to correct traits or bring in traits their breeding stock may lack.

Some individuals may share desirable characteristics, but they inherit them differently. This is especially true of polygenic traits, such as ear set, bite, or length of forearm. Breeding two phenotypically similar but genotypically unrelated dogs together would not necessarily reproduce these traits. Conversely, each individual with the same pedigree will not necessarily look or breed alike.

Breedings should not be planned solely on the basis of the pedigree or appearance alone. Matings should be based on a combination of appearance and ancestry. If you are trying to solidify a certain trait – like topline – and it is one you can observe in the parents and the linebred ancestors of two related dogs, then you can be more confident that you will attain your goal.

GENETIC DIVERSITY

Some breed clubs advocate codes of ethics that discourage linebreeding or inbreeding, as an attempt to increase breed genetic diversity. This position is based on a false premise. Inbreeding or linebreeding does not cause the loss of genes from a breed gene pool. It occurs through selection; the use and non-use of offspring. If some breeders linebreed to certain dogs that they favor, and others linebreed to other dogs that they favor, then breed-wide genetic diversity is maintained.

In a theoretical mating with four offspring, we are dealing with four gene pairs. The sire is homozygous at 50% of his gene pairs (two out of four), while the dam is homozygous at 75% of her gene pairs. It is reasonable to assume that she is more inbred than the sire.

A basic tenet of population genetics is that gene frequencies do not change from the parental generation to the offspring. This will occur regardless of the homozygosity or heterozygosity of the parents, or whether the mating is an outbreeding, linebreeding, or inbreeding. This is the nature of genetic recombination.

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There is a lack of gene diversity at the first (olive) gene pair, so that only one type of gene combination can be produced: homozygous olive. As the sire is homozygous lime at the third gene pair, and the dam is homozygous blue, all offspring will be heterozygous at the third gene pair. Depending on the dominant or recessive nature of the blue or lime genes, all offspring will appear the same for this trait due to a uniformity of heterozygosity.

If offspring D is used as a prolific breeder, and none of the other offspring are bred to a great extent, gene frequencies in the breed will change. As dog D lacks the orange gene in the second pair and the purple gene in the fourth pair, the frequencies of these genes will diminish in the breed. They will be replaced by higher frequencies of the red and pink genes. This shifts the gene pool, and the breed’s genetic diversity. Of course, dogs have more than four gene pairs, and the overuse of dog D to the exception of others can affect the gene frequency of thousands of genes. Again, it is selection (for example of dog D to the exception of others), and not the types of matings he is involved in that alters gene frequencies.

Breeders should select the best individuals from all kennel lines, so as to not create new genetic bottlenecks. There is a tendency for many breeders to breed to a male; who produced no epileptics in matings to several epileptic dams, to an OFA excellent stud, or to the top winning dog in the show ring. Regardless of the popularity of the breed, if everyone is breeding to a single studdog, (the popular sire syndrome) the gene pool will drift in that dog’s direction and there will be a loss of genetic diversity. Too much breeding to one dog will give the gene pool an extraordinary dose of his genes, and also whatever detrimental recessives he may carry, to be uncovered in later generations. This can cause future breed related genetic disease through the founders effect.

Dogs who are poor examples of the breed should not be used simply to maintain diversity. Related dogs with desirable qualities will maintain diversity, and improve the breed. Breeders should concentrate on selecting toward a breed standard, based on the ideal temperament, performance, and conformation, and should select against the significant breed related health issues. Using progeny and sib-based information to select against both polygenic disorders and those without a known mode of inheritance will allow greater control.

Rare breeds with small gene pools have concerns about genetic diversity. What constitutes acceptable diversity versus too restricted diversity? The problems with genetic diversity in purebred populations concern the fixing of deleterious recessive genes, which when homozygous cause impaired health. Lethal recessives place a drain on the gene pool either prenatally, or before reproductive age. They can manifest themselves through smaller litter size, or neonatal death. Other deleterious recessives cause disease, while not affecting reproduction.

Problems with a lack of genetic diversity arise at the gene locus level. There is no specific level or percentage of inbreeding that causes impaired health or vigor. It has been shown that some inbred strains of animals thrive generation after generation, while others fail to thrive. If there is no diversity (non-variable gene pairs for a breed) but the homozygote is not detrimental, there is no effect on breed health. The characteristics that make a breed reproduce true to its standard are based on non-variable gene pairs. A genetic health problem arises for a breed when a detrimental allele increases in frequency and homozygosity.

GENETIC CONSERVATION

The perceived problem of a limited gene pool has caused some breeds to advocate outbreeding of all dogs. Studies in genetic conservation and rare breeds have shown that this practice actually contributes to the loss of genetic diversity. By uniformly crossing all “lines” in a breed, you eliminate the differences between them, and therefore the diversity between individuals. This practice in livestock breeding has significantly reduced diversity, and caused the loss of unique rare breeds. The process of maintaining healthy “lines” or families of dogs, with many breeders crossing between lines and breeding back as they see fit maintains diversity in the gene pool. It is the varied opinion of breeders as to what constitutes the ideal dog, and their selection of breeding stock that maintains breed diversity.

The Doberman Pincher breed is large, and genetically diverse. The breed has a problem with vonWillibrands disease, an autosomal recessive bleeding disorder. Some researchers estimate that up to 60% of the breed may be homozygous recessive for the defective gene, and the majority of the remaining dogs are heterozygous. Therefore, there is diminished genetic diversity in this breed at the vonWillibrands locus. A genetic test and screening program now exists for Doberman Pincher breeders. They can identify carrier and affected dogs, and decrease the defective gene frequency through selection of normal testing offspring for breeding. By not just eliminating carriers, but replacing them with normal testing offspring, genetic diversity will be conserved.

Dalmatians have a high frequency defective autosomal recessive gene controlling purine metabolism. Homozygous recessive individuals can have urinary problems due to urate bladder stones and crystals, and an associated skin condition (Dalmatian Bronzing Syndrome). At one time, the breed and the AKC approved a crossbreeding program to a few Pointers, to bring normal purine metabolism genes into the gene pool. The program was abandoned for several reasons, but it was accepted that the number of individual Dalmatians with two normal purine metabolism genes far exceeded the few Pointers that were being used in the program. The impact of other Pointer genes foreign to the Dalmatian gene pool could have had a greater detrimental effect than the few normal purine metabolism genes being imported through the program.

PUTTING IT ALL TOGETHER

Decisions to linebreed, inbreed or outbreed should be made based on the knowledge of an individual dog’s traits and those of its ancestors. Inbreeding will quickly identify the good and bad recessive genes the parents share in the offspring. Unless you have prior knowledge of what the pups of milder linebreedings on the common ancestors were like, you may be exposing your puppies (and puppy buyers) to extraordinary risk of genetic defects. In your matings, the inbreeding coefficient should only increase because you are specifically linebreeding (increasing the percentage of blood) to selected ancestors.

Don’t set too many goals in each generation, or your selective pressure for each goal will necessarily become weaker. Genetically complex or dominant traits should be addressed early in a long-range breeding plan, as they may take several generations to fix. Traits with major dominant genes become fixed more slowly, as the heterozygous (Aa) individuals in a breed will not be readily differentiated from the homozygous-dominant (AA) individuals. Desirable recessive traits can be fixed in one generation because individuals that show such characteristics are homozygous for the recessive genes. Dogs that breed true for numerous matings and generations should be preferentially selected for breeding stock. This prepotency is due to homozygosity of dominant (AA) and recessive (aa) genes.

If you linebreed and are not happy with what you have produced, breeding to a less related line immediately creates an outbred line and brings in new traits. Repeated outbreeding to attempt to dilute detrimental recessive genes is not a desirable method of genetic disease control. Recessive genes cannot be diluted; they are either present or not. Outbreeding carriers multiplies and further spreads the defective gene(s) in the gene pool. If a dog is a known carrier or has high carrier risk through pedigree analysis, it can be retired from breeding, and replaced with one or two quality offspring. Those offspring should be bred, and replaced with quality offspring of their own, with the hope of losing the defective gene.

Trying to develop your breeding program scientifically can be an arduous, but rewarding, endeavor. By taking the time to understand the types of breeding schemes available, you can concentrate on your goals towards producing a better dog.

Further Reading:

If you are interested in learning more about these subjects, consult the following books:

  • Abnormalities of Companion Animals: Analysis of Heritability
    C.W. Foley, J.F. Lasley, and G.D. Osweiler, Iowa State University Press, Ames, Iowa. 1979.
  • Genetics for Dog Breeders
    F.B. Hutt, W.H. Freeman Co, San Francisco, California. 1979.
  • Veterinary Genetics
    F. W. Nicholas, Clarendon Press, Oxford England. 1987.
  • Genetics for Dog Breeders
    R. Robinson, Pergamon Press, Oxford England. 1990.
  • Genetics of the Dog (equally applicable to cats & other animals)
    M.B. Willis, Howell Book House, New York, New York. 1989.

Dr. Bell is director of the Clinical Veterinary Genetics Course for the Tufts University School of Veterinary Medicine and national project administrator for numerous genetic disease control programs of pure-bred dogs. He performs genetic counseling through Veterinary Genetic Counseling and practices small animal medicine in Connecticut. He and his wife breed Gordon Setters. This article can be reprinted with the permission of Dr Bell (Jerold.Bell@tufts.edu)

Genetic Testing While Preserving the Best Breed Qualities – Let’s Start the Conversation

One of the most controversial topics, and the most difficult to teach about breeding, is the use of genetic testing and the application of those test results when choosing a mating pair to “improve and preserve the breed”. This is an area where it can often appear, especially to the less experienced breeder, that some prominent and successful breeders are talking out of both sides of our mouths. From one side we say genetic testing is a must if you intend to breed, and then from the other side we say “oh, but don’t throw the baby out with the bathwater” just because the dog is a carrier or affected doesn’t mean they shouldn’t be bred. Improving and preserving the Gordon Setter breed, is nowhere near as simple as choosing to mate only those dogs who pass every genetic clearance. Making the right breeding decision, finding the right sire for a dam… well it’s just not a black or white, right or wrong decision process. So, we’re going to say here, that the first and the most important thing a potential breeder needs to learn, before making breeding decisions, before assuming that the right choice is to breed only those dogs who clear every genetic test, the first thing that potential breeder needs to learn and completely understand is what constitutes a mediocre dog, a good dog and a great dog. With this understanding, one can then come prepared to recognize why, and when it is imperative to include great dogs in the gene pool – and yes, even those good and great dogs who did not clear every genetic hurdle may be needed in that gene pool. Remember, these dogs have many other qualities that are vital to preserving and improving the breed.

Photo by Bob Segal
Photo by Bob Segal

I read an article by Brian Lynn published by Paw Print Genetics that spoke about this topic. I’m sharing Brian’s article here as it fits with what I wanted us to be thinking, learning and talking about…how to use genetic testing appropriately, especially at a time when we must always consider the shrinking size of our breed population and thus our gene pool. We do need to encourage and promote genetic testing. We do NOT need to eliminate every dog who is affected or a carrier, but we do need to aptly apply the judicious choice of the appropriate breed qualities in the dogs we chose to breed. Breeders also need to be able to share every genetic test result on every dog, and they should be able to do so without fear of censor by their peers. The behaviors that cause our breed harm…breeders who cover or omit negative test results…and breeder/exhibitors who gossip about or denounce their peers who have shared information honestly and freely. Compete in the ring with each other folks, we don’t need to compete with each other over breeding choices, stud services and the like, there simply aren’t enough of us left to be that cut throat toward each other.

“When we breed to better a line of purebred dogs, many intangible or subjective variables come into play – conformation, athleticism, intelligence, trainability and more. Mentoring and experience, even the gut instinct borne from these teachings, can make assessing those variables easier. As we learn more and develop an eye for evaluating and reading dogs, the standards for what constitutes a ‘better’ dog, one worthy of breeding, usually rise. The comparative knowledge experience brings allows us to differentiate a ‘great dog’ from a ‘good’ one; what might have been an acceptable to us a decade ago, might not make the cut today. And therein creates the economic correlation of supply and demand among top breeders.

As we eliminate potential breeding partners in favor of ‘better’ dogs, those that will truly improve a line and therefore breed, fewer and fewer potential partners exist. That makes the remaining pool of dogs more desirable and valuable.

When the qualities that elevated a dog to the top of the gene pool are combined with the objective results of canine genetic screening, a breeder is truly ‘bettering the breed’ by passing along the best physical and mental qualities the dog possesses while reducing or eliminating detrimental genes.

However, some people believe genetic testing poses the risk of reducing the gene pool of quality dogs too much. Certainly, if you were to remove every dog that was determined to be an affected or a carrier of an inherited disease, that upper echelon of dogs within a breed could theoretically bottleneck (especially if it’s a small gene pool to begin with); and/or leave dogs that don’t complement and strengthen each other consistently enough to better the breed across necessary qualities, regardless of genetic diversity. True, the knowledge of genetic mutations in two dogs could prevent a top-notch breeding from taking place, but in the big picture of bettering a line and breed, that’s a small concession.

But that’s not how genetic screening works. Genetic screening of canines for inherited diseases provides the knowledge to breed responsibly and with scientific evidence. Breeding to a carrier, or especially affected, dog is a personal decision each of us must weigh, but it can be done safely. Using genetic science, we can determine the mode of inheritance, as well as the variability and expressivity of a gene. With the knowledge of today’s science, we can breed smarter and safer than ever before.

Genetic screening makes a dog a known quantity. Combined with its physical, mental and psychological qualities, genetic screening allows for healthier decision-making choices that truly ‘better the breed.’ The fact that a dog is a known quantity in a gene pool makes it more valuable; a dog’s accomplishments set it apart from the general population, and genetic screening, regardless of results, put it in an even more elite pool of dogs.” read more here

So, this is where the conversation turns to you. I’ve said my small piece and offered food for thought through Brian’s article. Time for you all to join in here and share your thoughts, opinions and questions.

Photographs by Bob Segal

Sally Gift, Mesa AZ

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