Category Archives: Health & Genetics

Let’s Talk Linebreeding

“One of the most bandied about terms among breeders today seems to be linebreeding. Despite it’s widespread use, however, linebreeding is frequently misunderstood and miscommunicated; in fact, it is not altogether uncommon for an outcrossed pedigree to be mistakenly viewed as linebreeding by the novice. The present discussion defines linebreeding and how we can more accurately define our linebred litters.”

From – “Let’s Talk Linebreeding” written by Claudia Waller Orlandi, Ph.D. published in ‘Tally Ho’ the Basset Club of America Newsletter (July-August ’97). The online article may be found by clicking here.

(While this article was written with the Basset Hound breeder in mind, one can change the name to  Gordon Setter, or any breed for that matter, as the material is “one size fits all” when it comes to the topic of breeding.)

Linebreeding and Inbreeding: A Family Affair

Inbreeding and Linebreeding involve the mating of animals within the same family. Breeding relatives is used to cement traits, the goal being to make the offspring homozygous (pure) for desirable characteristics. Homozygous dogs tend to be prepotent and produce offspring that look like themselves (Walkowicz & Wilcox 1994)

Willis (1989) defines Inbreeding as the mating of animals “more closely related to one another than the average relationship within the breed.” Inbred pairings would include brother/sister (the closest form) father/daughter, mother/son, and half-brother/half-sister.  Linebreeding involves breeding relatives other than the individual parents or brother and sisters. Typical linebred matings are grandfather/granddaughter, grandmother/grandson, grandson/granddaughter, great-grandmother/great-grandson, uncle/niece, aunt/nephew and cousin crosses. Linebreeding is a less intense form of inbreeding. Because of their focus on a dog’s potential genetic contribution, inbreeding and line breeding are termed genetic breeding systems.

figure-1-genetic-breeding-systems Definition:  For a dog to be linebred there must be an ancestor in the pedigree that is common to both the sire and the dam.  Figure 2 illustrates this concept. Kelly is linebred because the dog, Brahms, appears twice in the sire’s side and once in the dam’s side of the pedigree.figure-2-linebreedingCommon Misconception:  A pedigree may show either the sire and/or the dam to be linebred but no ancestor common to both the sire and dam. This is outcrossing, not linebreeding (see figure 3).  Similarly, because the same kennel prefixes (Windy, Hill, Castle) are common to both the sire’s and dam’s ancestors, the newcomer may mistakenly view the pedigree as linebreeding.figure-3-outcrossingWhere to draw the “Line”?

Breeders do not always agree on what constitutes linebreeding, with some feeling that common ancestors within the first five or six generations is linebreeding. Willis (1989) indicates that the farther back linebreeding is in a pedigree the less intensive it will be, pointing out that a dog appearing 12 times (out of a possible 32) in the 6th generation of a pedigree would have a Coefficient of Inbreeding (CI) of only 1.8% (by comparison, a sire to a granddaughter cross has a CI of 12.5%). The CI tell us the proportion of genes for which the inbred ancestor is likely to be homozygous, that is carrying the same genes from each parent. (Remember that homozygous animals have a higher potential for reproducing themselves.) In Willis’s (1992) view, a common ancestor farther back than the 2nd or 3rd generation will have little influence on the litter. Linebreeding beyond the fourth generation has even less genetic impact.

How much bang will we get for our buck (or Basset!)

Several modern writers (Walkowitz & Wilcox 1994; Willis 1992, 1989; Onstott 1962) view linebreeding and inbreeding as essentially the same  and differing only in degree of intensity. Whether one considers inbreeding and linebreeding to be the same or feels they are two distinct breeding systems, quantifying the degree to which an animal is linebred (or inbred) provides important information regarding its potential genetic contribution. As Willis (1989) states: “When describing inbreeding [or linebreeding] breeders often say their dog is inbred or linebred without further qualification. This is a very inadequate description. We need to know which dog the animal is inbred [linebred] to and the degree of inbreeding [linebreeding].” Put another way, how much “bang” will we get from our linebreeding?

Describing your Basset’s linebred pedigree: reading, writing and a little arithmetic!

Willis (1992) suggests that a concise yet meaningful way to express the extent of linebreeding (inbreeding) is to number the generations of the animal in question. The common ancestor(s) is assigned the generation number as he/she appears in the pedigree. The parents are the first generation (1), the grandparents are the second (2), great grandparents are the third (3), great-great-grandparents are the fourth (4) and so on.

As previously stated, Kelly’s pedigree (Figure 2) is an example of  linebreeding, with Brahms appearing on both the sire’s and dam’s side. On the sire’s side Brahms appears twice in the third generation (3). We can write this as 3.3. On the dam’s side, Brahms appears once in the second generation (2) and this is written simply as 2. Willis has suggested the following written and verbal formats for expressing the extent of line breeding in a pedigree:

Written Format

We would write: “Kelly is linebred on Brahms 3.3/2”

Verbal Format

We would say: “Kelly is linebred on  Brahms three, three TO two.”

In the Written Format notice we separate the sire’s and dam’s side of the pedigree by using a slash mark (think of a pencil making a slash mark); in the Verbal Format the word “TO” is used to separate the sire’s and dam’s side (think of talking “to” someone). This verbal and written format tells us the dog on which Kelly is linebred and the extent of the linebreeding. Smaller numbers indicate that a dog is more closely linebred; larger numbers of 4 and above (Willis 1989) indicate a lesser extent.

Linebreeding and pedigrees: a final caveat

Linebreeding and inbreeding are essentially the same, differing only in the degree of intensity. (In Willis’s view, the common ancestors beyond the 2nd and 3rd generations will not greatly influence the resulting litter.) We have described the ease with which an animal’s extent of linebreeding may be expressed by means of written and verbal models. Perhaps this format will be “adopted” by those Basset Hound breeders whose interest lies in linebreeding. In addition to facilitating the description of a linebred pedigree over the phone, it certainly provides important information regarding the potential outcome of a breeding. In this regard, two things bear repeating: (1) linebreeding (and inbreeding) are only as viable as a breeder’s knowledge of basic genetics (a topic which will be addressed in future columns) and (2) a linebred pedigree is only as valuable as a person’s ability to determine the virtues and faults of the dogs it contains. When we add the final ingredient of rigorous selection hopefully we are on the way to producing better Basset Hounds!

References

Onstott, K. 1980. The New Art of Breeding Better Dogs. Howell, New York.

Walkowicz, C. and Wilcox, B. 1994 Successful Dog Breeding. Howell, New York.

Will, M.B. 1968 A simple method for calculating Wright’s coefficient of inbreeding. Rev. Cubana Cienc.Agric. (Eng.Ed.) 2: 171-4

Willis, M.B. 1989 Genetics of the Dog. Howell, New York

Willis, M.B. 1992. Practical Genetics for Dog Breeders. Howell, New York

For more articles about breeding by Claudia follow the link below.

These articles were written by Claudia Waller Orlandi, Ph.D. All have been published in ‘Tally Ho’, the official newsletter of the Basset Hound Club of America

Thank you to Barbara Manson, WI for sharing this link with us.

Sally Gift, Mesa AZ

Photography by Susan Roy Nelson

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Musings on Color

The following includes many excerpts from the article “Musings on Color” published on the blogspot Musings of a Biologist and Dog Lover written by Stephanie.

I’ve added my own thoughts and comments to embellish and round out the information for the Gordon Setter lover and breeder.

Setters 1805 - sydenham-edwards-the-setter-1805
This 1805 depiction of “setters” appears in the Cynographia Britannica. Note the black and tan setter and the red setter with the white face. The white dogs was also considered a Setter and it is speculated that these may all be litter mates.

Musings of a Biologist and Dog Lover

Sunday, July 1, 2012

The Gordon setter is one of a small number of setter breeds, which also includes the English setter, Irish setter, and Irish red and white setter. Though the Gordon Setter now only comes in one acceptable color, the breed’s history included a number of other colors that are now considered to be mismarks. Part of why these colors are in the breed is due to its relationship with the other setters. So, what are these mismarks?

Dogs with more or less than than required in the standard  

*Based on the current breed standard the Gordon Setters depicted in this artwork from the 1940’s carry too much tan.

Inherited on the Brown locus, a dog must be bb to be liver

Liver Gordon
Liver colored Gordon Setter

 

Inherited on the Extension locus, a dog must be ee to be recessive red

Barn hunt image 2
Red Gordon Setter

 

Inherited on the Spotting locus, a dog with a variety of genotypes can have too much white

Looking at these mismarks, they are all recessively inherited except in dogs that are genetically solid but have too much residual white. All of theses colors were well known when the breed was young. Much like the Irish setter, the predominant color in the early years of the breed is actually not what you think it would be when looking at modern dogs. Gordons were once mostly tricolor with some dogs being solid black and tan, liver, or red, but the white markings and other colors fell out of favor and led to the production of the breed you see today.

The current breed standard for the Gordon only allows for black and tan dogs with specific tan markings. Dogs that are anything other than black and tan are disqualified and anything more than a small bit of white on the chest is not allowed. A dog with more or less than the required tan would be penalized, despite the fact that tan markings can vary greatly on dogs that are all genetically tan pointed. So far, it is known that there are modifiers that control this amount of tan, but it isn’t known where they are or how they are inherited.

This is a case where color standard is based on, basically, fashion. What once was popular was no longer liked by those who wrote the breed standard, and thus those other colors faded into obscurity. However, since the colors are basically all recessively inherited, they continue to pop up on occasion in litters that are born today. These past decisions are really problematic when looking at the breed’s history and what this holds for the future.   Stephanie


Sally says…It is at this point that as a breeder of Gordon setters I would step in to say that I disagree with Stephanie’s call that the Gordon’s color standard (black and tan) is based on fashion and that this preference is problematic for the breed.

The color preference written into the standard was developed well over a century ago by avid bird dog breeders. They didn’t have an eye to fashion when it came to writing their standard, but they did know exactly what kind of dog they wanted to hunt over, as well as why those traits, written into the standard, were important to them. It has been my understanding that the vivid black and tan coloring of the Gordon Setter may have been written into the standard as the preferred color because of it’s contrast to the gold, tan and red foliage of the fall hunting season, the black dog contrasting, standing out against the fall foliage, making it far easier for the hunter to follow the dog while he worked the field. A red or buff dog, even a white and tan dog would more easily blend into the foliage, his coat acting to camouflage him as he worked the field. And, with the deaf link to the white gene it is certainly understandable why white was weeded out as an allowed color.

If there are other history buffs out there who can offer more insight as to the color preference we’d love to hear your thoughts and hope you’ll share those and any references for us in the comment section of this article.

Anita Aronsson, Sweden shared this stunning link to photos of Gordon Setters in many colors and patterns, be sure to check it out by clicking here!

We’d also welcome your photos, if you have some to share, of red, liver, or other mismarked Gordons to be shared here to help others learn.  Please email those to us at gordonsetterexpert@gmail.com, we will respect your privacy and photos can be published anonymously.

Charlie Royster was kind enough to share this example of Gordon Setter color photo with usColor example

Sally Gift, Mesa AZ

 

 

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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.

Blastomycosis—What Every Dog Owner Needs to Know – Life with Llewellin Setters

Blastomycosis, or Blasto as it is often called, is a very serious and potentially deadly, systemic fungal disease that can affect dogs, humans, and other mammals. Blasto is caused by inhaling the spores of the fungus Blastomyces dermatitidis. B. dermatitis grows as a mold in acidic, organically rich …

Source: Blastomycosis—What Every Dog Owner Needs to Know – Life with Llewellin Setters

This Substance Is Making Dogs Sick, and It’s Probably in Your Home Right Now – American Kennel Club

This post contains a link to, and excerpts from, the article published by the AKC, Dog Health. Please be aware of the substance and danger, read the entire article by clicking here:

This Substance Is Making Dogs Sick, and It’s Probably in Your Home Right Now – American Kennel Club

Dangers Of Xylitol

EXCERPTS:

A substance called xylitol is making thousands of dog sick and even causing death…something this benign, an ordinary sweetener, could be toxic to pets.

What Is Xylitol?

Xylitol is a sugar substitute most often associated with “sugar-free” chewing gum and mints, but it’s also found some brands of peanut butter, toothpastes, certain medications, and vitamins, many sugar-free products (chocolate, JELLO, yogurt, pudding), and even some household products such as baby wipes and lip balm. A comprehensive list of products is available here. VCA Hospitals reports that xylitol is 100 times more toxic to dogs than chocolate.

Why Is Xylitol So Dangerous?

According to Caroline Coile, AKC Family Dog Nutrition & Health columnist: “The dog’s pancreas confuses xylitol with real sugar and releases insulin to store it. The insulin removes real sugar from the bloodstream and the dog can become weak, and have tremors and even seizures starting within 30 minutes of eating it.” Other symptoms of hypoglycemia include poor coordination and vomiting/diarrhea.

Liver failure (and death) can also result from xylitol ingestion, and symptoms can take as much as eight hours as show up. A dog only needs to consume a very little amount of xylitol to receive a deadly dose. As much as two pieces of gum can cause a problem in a small-breed dog.

 

Excerpts from and links shared by Sally Gift, Mesa AZ

Photograph by Susan Roy Nelson

 

 

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.)

Bell 6 Pedigree

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)

Small Population Breeds and Issues of Genetic Diversity

bell-jerold-1520260577 By Jerold s Bell DVM, Clinical Associate Professor of Genetics, Tufts Cummings School of Veterinary Medicine.  Reprinted by permission of the author.

(This article was originally published in the March 2007 AKC Perspectives Delegates Newsletter.)

Issues of genetic diversity are a concern to dog breeders, and this can be especially so for breeds with small populations. The concern is whether there is enough genetic variation within a breed’s gene pool to maintain health and vitality. Breeders should be concerned about genetic diversity, because there are examples where damage has been done to a breed due to breeding practices. Restriction of genetic diversity can also occur in large population breeds.

All genes come in pairs: one from the sire and one from the dam. Each gene in the pair is called an allele. If both alleles in a pair are of the same type, the gene pair is homozygous. If the two alleles are different, the gene pair is heterozygous. While each dog can have a maximum of two different alleles at a gene pair, many different alleles are potentially available to be part of the gene pair. The greater the number of alleles that are available at each gene pair (called genetic polymorphism), the greater the genetic diversity of the breed.

If there is no breed diversity in a gene pair, but the particular homozygous gene that is present is not detrimental, there is no negative effect on breed health. The characteristics that make a breed reproduce true to its standard are, in fact, based on non-variable (that is, homozygous) gene pairs.

The origins of the breeds have a lot to do with genetic diversity. A breed established with a working phenotype tends to have diverse founder origins, and significant diversity. Even with substantial population bottlenecks, the breed can maintain considerable amounts of genetic diversity. This was shown in a molecular genetic study of the Chinook breed, which was reduced to 11 modern founders in 1981. Breeds established by inbreeding on a limited number of related founder individuals could have a reduced diversity. Many breeds have also gone through diversity reducing bottlenecks; such as occurred during World War II. For most of these breeds, their gene pools have expanded through breeding for many generations, resulting in a stable population of healthy dogs.

There are two factors that must be considered when evaluating genetic diversity and health issues in a breed; the average level of inbreeding, and detrimental recessive genes. With a small population, there is a tendency to find higher average inbreeding coefficients due to the relatedness between dogs from common ancestors. There is, however, no specific level or percentage of inbreeding that causes impaired health or vigor. The problems that inbreeding depression cause in purebred populations stem from the effects of deleterious recessive genes. If the founding population of a breed produces a high frequency of a deleterious recessive gene, then the breed will have issues with that disorder. This can be seen as smaller litter size, increased neonatal death, high frequency genetic disease, or impaired immunity. If these issues are present then the breed needs to seriously consider limited genetic diversity.

The issue of high average inbreeding coefficients is one that all breeds go through during their foundation. As the population increases and the average relatedness of dogs goes down (based on a fixed number of generations), the average inbreeding coefficient for the breed will go down. The effect of initially higher inbreeding coefficients in small population breeds will depend on the presence of deleterious recessive genes that will be expressed when homozygous.

Some breeders discourage linebreeding and promote outbreeding in an attempt to protect genetic diversity in their breed. It is not the type of matings utilized (linebreeding or outbreeding) that causes the loss of genes from a breed gene pool. Rather, loss of genes occurs through selection: the use and non-use of offspring. If a breed starts limiting their focus to breeding stock from a limited number of lines, then a loss of genetic diversity will occur.

The process of maintaining healthy lines, with many breeders crossing between lines and breeding back as they see fit, maintains diversity in the gene pool. If some breeders outbreed, and some linebreed to certain dogs that they favor while others linebreed to other dogs that they favor, then breedwide genetic diversity is maintained. It is the varied opinion of breeders as to what constitutes the ideal dog, and their selection of breeeding stock based on their opinions, that maintains breed diversity.

The most important factor for diminished genetic diversity in dog breeds is the popular sire syndrome. The overuse of a popular sire beyond a reasonable contribution through frequent breedings significantly skews the gene pool in this direction, and reduces the diversity of the gene pool. Any genes that he possesses – whether positive or negative – will increase in frequency. Through this founder’s effect, breed related genetic disease can occur. Another insidious effect of the popular sire syndrome is the loss of genetic contribution from quality, unrelated males who are not used for breeding. There is a finite number of quality bitches bred each year. If one male is used in an inordinate amount of matings, there will be fewer females left for these quality males that should be contributing to the gene pool. The popular sire syndrome is a significant factor in both populous breeds and breeds with small populations.

The best methods for ensuring the health and diversity of a breed’s gene pool are to:

  1. Avoid the popular sire syndrome.
  2. Utilize quality dogs from the breadth of your population to expand the gene pool.
  3. Monitor genetic health issues through regular health surveys.
  4. Do genetic testing for breed-related disorders.
  5. Participate in open health registries, such as CHIC (www.caninehealthinfo.org) to manage genetic disorders.

 

(This article can be reprinted with the written permission from the author: jerold.bell@tufts.edu)

Related article – Outcrossing Does Not Equal Gene Pool Diversity

Photograph courtesy of Susan Roy Nelson is not intended to illustrate any point in the article, it is presented for your viewing pleasure only.

 

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Outcrossing Does Not Equal Gene Pool Diversity

In previous articles we’ve talked about the shrinking population of the purebred dog and specifically about how much smaller the Gordon Setter population is today – over 70% fewer Gordons than twenty years ago. The current bottleneck in the number of Gordon Setters available for breeding calls for us, as responsible breeders, to evaluate each mating more carefully to determine if it will accomplish our own goals while also considering the impact our mating will have on the breed gene pool. As breeders in today’s world we are not only charged with improving the breed, we are also called upon to ensure that our breeding activity has a positive impact on the preservation of the breed gene pool.  The good news my friends, is that all of this can be less painful to accomplish than you might have thought.

For topics like this I call on experts for advice, and I am grateful to Jerold S. Bell DVM, Clinical Associate Professor of Genetics, Tufts Cummings School of Veterinary Medicine for the guidance he’s offering. Jerry’s article Small Population Breeds & Issues of Genetic Diversity is the resource used for this article and is quoted here, and reprinted entirely elsewhere on the blog with his permission. (Click the title above to link to that article.)

Has the Gordon Setter population reached a level where we should consider it a “small population breed”? Perhaps not, yet..who’s to say? The point here is that the population of the Gordon Setter has shrunk dramatically (Honey, I Shrunk the Kids!) and as it is now substantially smaller, breeders must be aware of how important our breeding choices become when viewed in terms of the health of our breed gene pool. Just as there are fewer Gordon Setters, so too are there far fewer breeders bearing the responsibility for their preservation. With fewer breeders we find that many of the older lines are harder if not impossible to find today.

Jerold S. Bell DVM –  *Issues of genetic diversity are a concern to dog breeders, and this can be especially so for breeds with small populations. The concern is whether there is enough genetic variation within a breed’s gene pool to maintain health and vitality. Breeders should be concerned about genetic diversity, because there are examples where damage has been done to a breed due to breeding practices. Restriction of genetic diversity can also occur in large population breeds.

Putting a lesson in genetics aside for another time, let’s talk today about genetic diversity in our breed gene pool.  Quoting Jerold S. Bell DVM  * There are two factors that must be considered when evaluating genetic diversity and health issues in a breed; the average level of inbreeding, and detrimental recessive genes. With a small population, there is a tendency to find higher average inbreeding coefficients due to the relatedness between dogs from common ancestors. There is, however, no specific level or percentage of inbreeding that causes impaired health or vigor. The problems that inbreeding depression cause in purebred populations stem from the effects of deleterious recessive genes. If the founding population of a breed produces a high frequency of a deleterious recessive gene, then the breed will have issues with that disorder. This can be seen as smaller litter size, increased neonatal death, high frequency genetic disease, or impaired immunity. If these issues are present then the breed needs to seriously consider limited genetic diversity. 

In this statement then, as a group of dedicated breeders, we find a key to issues or symptoms, whose frequency of expression within the breed need monitoring. An increase or spike in these symptoms throughout the breed population, that goes beyond normal expectations, should be a cue that breeders need to seriously consider if we are experiencing limited genetic diversity in our breed gene pool. As a group we must be willing to share our breeding experiences with a wide audience of our peers. Additionally, we must understand that GSCA Health and Genetics committee surveys are also a vital indicator of the breed health, especially as it pertains to breed gene pool diversity.

As we talk about gene pool diversity, we may find some breeders who discourage linebreeding and promote outcrossing (outbreeding) as the way to protect genetic diversity in the breed. While this does sound like an easy, and maybe even an obvious answer, outbreeding would not provide the complete solution.

Jerold S. Bell DVM – *It is not the type of matings utilized (linebreeding or outbreeding) that causes the loss of genes from a breed gene pool. Rather, loss of genes occurs through selection: the use and non-use of offspring. If a breed starts limiting their focus to breeding stock from a limited number of lines, then a loss of genetic diversity will occur.

The process of maintaining healthy lines, with many breeders crossing between lines and breeding back as they see fit, maintains diversity in the gene pool. If some breeders outbreed, and some linebreed to certain dogs that they favor while others linebreed to other dogs that they favor, then breedwide genetic diversity is maintained. It is the varied opinion of breeders as to what constitutes the ideal dog, and their selection of breeeding stock based on their opinions, that maintains breed diversity.

The most important factor for diminished genetic diversity in dog breeds is the popular sire syndrome. The overuse of a popular sire beyond a reasonable contribution through frequent breedings significantly skews the gene pool in this direction, and reduces the diversity of the gene pool. Any genes that he possesses – whether positive or negative – will increase in frequency. Through this founder’s effect, breed related genetic disease can occur. Another insidious effect of the popular sire syndrome is the loss of genetic contribution from quality, unrelated males who are not used for breeding. There is a finite number of quality bitches bred each year. If one male is used in an inordinate amount of matings, there will be fewer females left for these quality males that should be contributing to the gene pool. The popular sire syndrome is a significant factor in both populous breeds and breeds with small populations.

I believe as a whole, that Gordon Setter stud dog owners have worked hard to manage stud dogs properly to avoid the “popular sire syndrome”. This is not an easy task to manage as so many variables, including emotions come into play. Hats off to all who have kept a diligent and watchful eye on our breed through proper stud dog management.

As I look back at what Dr. Bell has written, I realize that our breed is fortunate to have had many breeders, both past and present, who have contributed much to preserve the Gordon Setter; sometimes they contributed matings that improved specific aspects of the breed and sometimes they contributed by using breeding practices that preserved genetic diversity. Moving forward, our breed needs us to continue to attract and mentor a diverse group of breeders who also possess an understanding of the principles of gene pool diversity. As we have seen, there is simply not one step or one action to preserve diversity, instead there is a collection of various actions, that when understood and followed by the individual breeder, with each breeder working alongside the many other breeders – it is when we work as a collective group that we accomplish that one common goal – preservation of the purebred Gordon Setter…oh, and don’t forget there is still improvement of the breed to consider!

Jerold S. Bell DVM writes:  *The best methods for ensuring the health and diversity of a breed’s gene pool are to:

  1. Avoid the popular sire syndrome.
  2. Utilize quality dogs from the breadth of your population to expand the gene pool. (as new genes cannot be added to a closed registry this refers to preserving genes that might otherwise be lost by selection of only a few sires out of the many available)
  3. Monitor genetic health issues through regular health surveys.
  4. Do genetic testing for breed-related disorders.
  5. Participate in open health registries, such as CHIC (www.caninehealthinfo.org) to manage genetic disorders.

Small Population Breeds & Issues of Genetic Diversity by Jerold S. Bell DVM

Photograph by Susan Roy Nelson shared for your viewing pleasure, is not intended to illustrate any point in the article.

 

 

 

 

Did Our Gene Pool Shrink (Again) in 2015?

In 2015 the number of AKC registered Gordon Setters continued it’s 20 year drop, down by another sixty dogs. Is there any end in sight to this trend, and are we seeing the first signs of extinction for some purebreds, including our own breed? In the last 20 years the Gordon Setter population has dropped by 71%. What is the impact to a breed like ours when 71% of their population is no longer available for breeding?

In the U.K., The Kennel Club considers the Gordon Setter as a “vulnerable” breed at only 234 registrations in 2015. I’m wondering how we should label the Gordon here in the states, considering that the population of the U.S.,  319 million, is nearly five times that of the U.K. at 64 million, but the U.S. Gordon Setter at 381 new registrations is only about one and a half times the 234 registrations in the U.K., a significantly smaller per capita number.

Could this mean that the breed is in an even more precarious and vulnerable position in the U.S.?

With this alarming decline in the breed’s population, if you’re breeding Gordon Setters there are a few things to consider as you go about planning new litters, and one of those considerations includes the need to develop a good understanding the of the gene pool and how your choices will impact preservation of the breed.

Your next litter is like a big fish in a small pond. As there fewer and fewer Gordon Setters whelped each year, the overall number of Gordon Setters available for breeding is dropping to an all time low, so litters that are born now will have a bigger impact on the future and preservation of the breed than the many litters that were born 20 years ago. Is it possible that we are losing genetic diversity in our breed population due to the decline in the overall number of new litters produced, and that our gene pool might also be shrinking? Unfortunately that answer may be Yes.

As breeders then, we need to ensure we have a basic understanding of genetic concepts and what it means to maintain genetic diversity. As our pool of fertile dogs continues to decline in number, the chance of finding unrelated genetically diverse dogs has fallen dramatically, which becomes especially relevant if we later find we need those dogs to help resolve a health issue from a newly recognized gene mutation.

Just as we pay attention to the need for health clearances when preparing for a litter, so too must we pay similar attention to understanding and analyzing the pedigrees of the resulting litter. Now is the time when we need to embrace the concept of preserving  offspring from the bloodlines of many various kennels and engage in preserving semen from healthy dogs of good quality, preserving many dogs of good quality from both show and field, not only those who are our top winners. Should we be doing more and more blending of the typical show and the field lines, or importing semen or dogs from other countries? These tactics and many more, now more than ever before need our attention, as breeders work to preserve the best qualities of our gorgeous breed, along with the diversity in our gene pool needed to safely continue the Gordon Setter in a healthy state.

With all that said, the following is an excellent article to get you started from The Institute of Canine Biology. It is a basic discussion about the gene pool. Today’s “Required Reading” for every Gordon Setter breeder I do believe!

What’s in the Gene Pool?

The founding of the breed – the Gene Pool

pool.jpgLet’s pretend these 11 dogs are the “founders” of your breed – they are the first dogs entered into the studbook.  All subsequent members of the breed are descended from these dogs only.  The breed has a closed gene pool.

All of the genetic variability that will ever exist in your new breed is present in these dogs.  Mutations probably won’t add new, useful genetic variation because most mutations are detrimental.  If the mutated gene is dominant and detrimental, it will likely be weeded out very quickly.  If the mutation is recessive, it is not expressed unless an animal is homozygous for the allele by inheriting a copy from each of its parents.  In the heterozygote condition, a mutated recessive allele can lurk in the genome for generations without ever causing a problem.  So, unless additional “founders” are added to the population at a later date, all of the genes you will ever have to work with in your breeding program are present in these dogs.

In each of these dogs there are at least a few (and perhaps many) recessive genes that could cause genetic disorders.  But these disorders will only expressed if a dog is homozygous for the disease allele – it must have TWO copies, one from each parent.  As long as the disease genes are rare in the population, very few animals will ever display the illness.

Can the gene pool get bigger? (No!)

Okay, starting with your 11 founder dogs, let’s let them reproduce.  To keep it simple, we will let them produce only identical copies of themselves – clones.

Now we have 27 dogs, all of which are exact copies of one of the founders.  What has happened to the size of the gene pool?

Nothing.pool1

You now have more dogs, and you now have more copies of the genes found in the dogs that had more offspring, like that busy gray dog with the red tongue.  So, the frequency of particular alleles is different in this population than in the founders, but the number of different alleles in the population is exactly the same.  (We’re ignoring the possibility of a mutation for now.)

What if the dogs reproduce normally instead of producing clones?  In sexual reproduction, each puppy receives one set of genes from each parent.  And, each puppy receives a different mix of parental genes, so each one is a bit different.  Also, each parent dog has a different number of offspring and might mate multiple times with different dogs.  So the frequency of the various alleles in the population could be very different in this new population than in the founders.

But again, even though there are now more dogs in the population, the gene pool does not get bigger.

In fact, it doesn’t matter how large this breed gets – it might someday grow to thousands of dogs – but as long as the stud book is closed, the gene pool will never be larger than it was when the breed is founded.

Can the gene pool get smaller?  (Yes!)

poo12The gene pool of a closed breed can never get bigger.  But it can get smaller.

What if dogs with black ears were less fertile, or had higher puppy mortality, or had some other biological problem?  The frequency in the population of the genes causing the black ears would be reduced by natural selection – black-eared dogs would contribute fewer copies of their genes to the next generation. Eventually, by genetic drift (chance) or natural selection, the genes in black-eared dogs would become rarer and rarer, and might eventually be eliminated from the population entirely.

What if breeders didn’t like black ears, so all the puppies with black ears were spayed or neutered and sent to pet homes?  Those alleles will become less frequent in the population, and they might be eliminated completely because of artificial selection courtesy of the breeder.

The gene pool gets smaller when genes are completely eliminated from the population.  It is unlikely that a gene will be restored by chance mutation, and the only other way it can be restored is if an animal is introduced into the breeding population that carries that gene and who reproduces successfully.

In purebred dogs, when the stud book is closed, no new alleles can be introduced into the breed.  The loss of an allele is permanent and reduces the heterozygosity in the genome for that gene.

http://www.instituteofcaninebiology.org/whats-in-the-gene-pool.html

Sally Gift, Mesa AZ

 

 

 

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