Vulnerable Dog Breeds Blog Series - Blog 3

A successful dog can be enormously valuable to a breed.

The problem begins when too many breeders decide that the same dog is the answer.

This is known as the popular sire effect. In simple terms, it happens when one male is used so extensively that his genetics become disproportionately represented throughout the breed. The Kennel Club describes popular sires as an important contributor to reduced genetic diversity and increased inbreeding, and research across pedigree dog populations has likewise shown that heavily used sires can make a very large genetic contribution to later generations.

The UC Davis Veterinary Genetics Laboratory also tracks genetic diversity in breeds like the Newfoundland, giving breeders a practical way to see how concentrated a population's genetics have become.

That does not mean a popular sire is a bad dog. Quite the opposite. He may be healthy, beautifully constructed, have an excellent temperament, produce well, or be highly successful in the show ring.

The problem is not necessarily the dog.

The problem is what happens when everybody follows him.

Why does one sire become so popular?

From my own years around pedigree dogs, show-ring success has often been one of the biggest drivers.

A dog starts winning. Judges reward him repeatedly. Breeders see those results and understandably think: that dog must have something worth using.

Then momentum builds.

One breeder uses him. Then another. Puppies from those matings begin appearing in the ring. Some of them win too. Suddenly the same dog, or close relatives of that dog, can appear through a surprising number of pedigrees.

That creates a very narrow lens through which a breed can begin making decisions.

A show win tells us something about how a dog was assessed on that day. It does not tell us everything about his genetic value to an entire population. Health, temperament, longevity, fertility, family history and how heavily his relatives are already represented matter too.

A good dog can still be overused.

When a popular sire stamps a look on a breed

There is another side to the popular sire effect that is easy to overlook. An influential dog does not only spread his pedigree through a breed. If he has a very recognisable look, and that look is rewarded in the show ring, he can also help spread a particular version of breed type.

Breeders sometimes talk about a sire “stamping” his puppies. Used carefully, that consistency can be valuable. But when the same dog, his sons and his close relatives are used again and again, a fashionable feature can become increasingly common. Judges then see more dogs carrying that look, breeders select for it, and over several generations the feature can begin to feel normal — even if it is more exaggerated than what was seen in the breed in the past.

The Bulldog is a useful example of the wider principle. Historical comparisons show that the modern Bulldog differs markedly from its more athletic ancestors, with selective breeding contributing to the much shorter, flatter face and other exaggerated features we now associate with the breed. More broadly, researchers have described how interpretation of breed type by breeders and judges can drift over time, so that features such as muzzle length become progressively more extreme.

That does not mean one famous sire created the modern Bulldog, nor that every popular sire pushes a breed towards exaggeration. It shows how quickly human preference can reshape a breed when the same desirable look is repeatedly rewarded and reproduced.

For a vulnerable breed, that gives us another question to ask alongside genetic diversity: are we preserving healthy, functional breed type, or are we simply reproducing the look that is fashionable right now?

The effect is often hidden for generations

One of the most useful things I learnt when I began calculating coefficients of inbreeding and studying pedigrees properly was just how often the same dogs appeared once I went back further.

At first glance, two dogs might look reasonably unrelated.

Go back four, five or six generations and suddenly the same influential sire appears again. Then again. Sometimes through different sons and daughters, so the repetition is not immediately obvious.

Keep going and you begin to see how much influence one animal has really had.

The effect is not simply about how many litters one male produces. His influence can continue through sons, daughters and later generations long after he is gone.

Research into Kennel Club pedigrees has shown why this matters. When a sire contributes heavily to the next generation, his genetic contribution is carried forward, and using a close male relative instead does not necessarily solve the problem because much of the same genetic material is still being repeated.

That is where pedigree depth matters.

It is also why vulnerable breeds need people willing to look beyond the obvious dog standing in the spotlight.

Look left and right of the famous dog

One of the most useful pieces of breeding advice I came across many years ago was to look to the left and to the right.

Do not only look at the famous sire.

Look at his brothers. Look at his sisters. Look at uncles, nephews, cousins and other branches of the family.

Sometimes the less fashionable relative has something you actually prefer.

Perhaps his front construction is better, his ear placement more correct, or his temperament stronger. He may offer many qualities you admire without concentrating the population around the exact same individual.

That does not mean choosing a poorer dog simply to be different.

It means asking a wider question: what else is available in this family, and what might preserve more options for the breed?

For vulnerable breeds, options are precious.

The dogs we do not use matter too

There is another part of this discussion that receives far less attention: the useful dogs that disappear from the breeding population before anybody realises they may have been important.

Over the years I have watched litters where many puppies were routinely neutered or spayed. Sometimes one or two were kept entire because they were considered the best prospects. If those dogs later failed to win, were never used, developed a problem, became infertile or died unexpectedly, the rest of that genetic branch might already have been permanently closed.

The litter existed, but the breeding options did not survive.

That is particularly significant in a vulnerable breed.

I am not suggesting every pet dog should automatically be bred from. Responsible breeding still requires thoughtful decisions around health, temperament, structure, welfare and suitable homes. But careful selection is different from automatically removing almost an entire generation from future consideration.

Once a genetic option is gone, it may be impossible to recreate it.

Why I have collected semen from dogs I may never use

That is one reason I have tried, where I could afford to, to collect and store semen from males even when I did not have an immediate breeding plan for them.

To me, semen storage is not necessarily about deciding that this dog must be used.

It is about keeping a door open.

Years later, that dog may prove useful to me, to another breeder, or to the breed itself. A mating that makes no sense today may make perfect sense two or three generations from now.

In a small population, semen storage can preserve an option precisely because we cannot predict what the breed will need later.

My approach has been simple: if I can preserve the genetics responsibly, I would rather have the choice and never need it than discover years later that the choice has disappeared.

Breeding cannot be about personalities

This is where the human side of vulnerable-breed preservation becomes uncomfortable.

Dog breeding communities can become cliquey. People fall out. Breeders form groups. Access to certain dogs can depend as much on relationships and personalities as it does on the suitability of a mating.

I experienced that myself.

There were breeders who did not take me seriously, despite years spent studying pedigrees, travelling to shows and kennels overseas and working as a veterinary nurse.

That experience taught me something I now believe very strongly:

Breeding is about working with people, not working against them and shutting them out.

You do not have to like everybody.

You do need to be able to have a conversation about the breed.

If two people genuinely want to preserve the same vulnerable breed, the starting point should be: what can these bloodlines contribute, and how can we protect useful options for the future?

Personal disagreements should not automatically erase genetics.

Look at the dog. Look at the pedigree. Look at the health and temperament. Look at what the mating could contribute. Then have the difficult conversation like adults.

The breed has to be bigger than our egos.

A popular sire is not the villain

I think this point is important because discussions about the popular sire effect can easily become accusatory.

The sire himself is not the problem.

Nor is a breeder automatically wrong for using an outstanding dog.

Sometimes a particular sire is exactly the right choice. He may strengthen something important or introduce genetics that are badly needed.

The danger comes when too many breeders make the same decision without considering the population-level consequence.

That is why the question should not simply be:

"Is this a good dog?"

It should also be:

"How much of this dog is already in the breed, and what choices will this mating leave behind?"

Those are two very different questions.

Preservation means keeping several roads open

In a vulnerable breed, breeding should not be a race to produce a single perfect line.

It should be about preserving enough healthy, functional, breed-typical lines that future breeders still have somewhere to go.

That may mean using a less fashionable relative, storing semen from a dog that is never used during his lifetime, keeping more than one promising puppy available to the gene pool, or collaborating with somebody you would not choose as a friend.

None of those decisions are particularly glamorous.

But preservation is rarely glamorous.

It is long-term work.

If we continually narrow a breed around the same successful dogs, we may eventually discover that we have bred ourselves into a corner.

If instead we keep looking left and right, preserve sensible alternatives and communicate across breeder groups, we give the next generation something far more valuable than another show winner.

We give them choices.

And for a vulnerable breed, choices are survival.

Founder perspective

I am Fiona Robertson, founder of Newflands. My perspective comes from decades of living with, breeding and studying dogs, my background as a veterinary nurse, and years spent researching pedigrees and bloodlines both in New Zealand and overseas.

This series is not about pretending there is one perfect formula for breeding. It is about opening up the conversations that matter when the population is small and every generation can change the choices available to the next one.

If you have not yet read the earlier articles in this series, start with What Is a Vulnerable Dog Breed? and then Why Genetic Diversity Matters in Vulnerable Dog Breeds. Together they explain why the popular sire effect matters so much in the first place.

Next in the series: Coefficient of Inbreeding - What It Tells You and What It Doesn't.

FAQs

What is the popular sire effect in dogs?
The popular sire effect happens when one male dog is used so extensively that his genetics become disproportionately common within a breed. Over generations, this can reduce the number of genuinely different breeding options available and can contribute to increasing relatedness within the population.

Does a popular sire have to be unhealthy?
No. A popular sire may be an excellent dog with strong health, temperament, structure or show results. The concern is not that the dog is necessarily poor quality. It is that excessive use of any one individual can narrow genetic diversity across the wider breed.

Can a popular sire change what a breed looks like?
Yes. If a sire has a very distinctive look and is used widely, especially when that look is repeatedly rewarded in the show ring, those features can become more common in later generations. Over time, breeders and judges may begin to see that look as normal breed type. This is why breeders need to consider not only genetic diversity, but also whether they are preserving healthy, functional breed characteristics rather than simply following fashion.

Can using a son or brother of a popular sire solve the problem?
Not necessarily. Close relatives share a substantial amount of genetic material, so repeatedly substituting sons, brothers or other close relatives may still concentrate the same family within the population. The deeper pedigree and the wider genetic contribution of that family need to be considered.

How can breeders reduce the popular sire effect?
Breeders can look beyond the most fashionable sire, consider suitable relatives from less-used branches, retain more breeding options where appropriate, study pedigrees beyond the first few generations, use genetic-diversity tools alongside health and temperament information, and collaborate so that valuable lines are not unnecessarily lost.

Is storing semen useful for a vulnerable breed?
It can be. Properly collected and stored semen can preserve genetic options after a dog is no longer alive or fertile. It does not mean the semen must be used, but it may give future breeders an option that would otherwise have disappeared.