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Cavaliers are in Trouble - The Institute of Canine Biology

By Carol Beuchat PhD

Since the action in Norway to ban breeding of Cavaliers because the heavy burden of health disorders violated their animal welfare act, there has been much heated discussion in these forums.

At the root of most health issues in dog breeds are the small size of the gene pool and high levels of inbreeding. Let me explain why these things are a problem. The Cavalier King Charles Spaniel was founded on only a handful of dogs. I've seen numbers of 6 and 8; let's just call it a handful.

If the stud book is closed, then all the genes the breed will ever have come from those few dogs.

Also, because the stud book is closed, dogs can only breed to related dogs. There are no "outcrosses" here; every dog is closely related to every other dog. It's a bit like trapping you and your immediate family on an island from which there is no escape. You can only breed with kin.

Over time, the animals in a closed population can ONLY become more closely related (genetically similar) to each other. Inbreeding can ONLY increase. Furthermore, gene variants are lost every generation through selective breeding and also just by chance. So the variation in the genes in those original 8 dogs is gradually lost over time. Eventually closed populations like this have such high levels of inbreeding that they are wrecked by health problems and infertility, and they simply go extinct.

In most societies, marrying your cousin is frowned upon. This is because your children would be inbred, at a level of 6.25%. For recessive mutations, that is also a risk of genetic disease at the same level of 6%. In most cultures, that disease risk is deemed too high, and these marriages can even be banned.
For half-sib pairings, the inbreeding produced in the offspring is higher, averaging 12%. Full-sib pairings produce offspring with inbreeding of 25%. For a recessive mutation in the genome, that is a 25% risk of producing an affected animal.

The problem with Cavaliers is that their level of inbreeding is extraordinarily high. We said that a full sibling cross resulted in inbreeding of 25%. I rounded up the data for two studies, one that included 10 dogs per breed based on US (mostly AKC registered) dogs Dreger et al (2016), and another that included data for 455 Cavaliers registered with the FCI, AKC, UKC, or the Kennel Club

( Bannasch et al., 2021). For the Dreger et al. dataset the inbreeding based on DNA for the Cavalier averaged 42.1% and for the Bannasch et al. data, inbreeding averaged 41.1%.
For two unrelated datasets, of very different sizes, the level of inbreeding in the Cavaliers was essentially the same. This reflects the high level of inbreeding and genetic similarity among the dogs. It really doesn't matter how you sample the population, the estimate of average inbreeding doesn't vary much.

Remember, 25% inbreeding results from a full sibling cross from unrelated parents. The level of inbreeding in Cavaliers is way - WAY - higher than that. Most people would not do a breeding of two littermates, but the inbreeding data show that in fact most breedings are between dogs much more closely related (i.e., genetically similar) than littermates.

We do DNA testing to identify carriers of mutations so we can avoid the 25% risk of producing a puppy that is homozygous for the mutation. We know that every animal has many mutations lurking in its genome, and we can't test for the ones we don't know about. But the probability of producing a puppy homozygous for an unknown mutation is going to be the same as from a known one. Cavaliers are all so closely related to each other that the average inbreeding produced in a puppy is 40% so the risk of homozogysity in a mutation is 40% as well.

Now, think about this. You do your DNA testing to avoid producing a puppy affected by a known mutation, which you can prevent entirely by not mating two carriers. But for all those unknown mutations in the genome, the risk of producing an affected puppy is the same as the average inbreeding, which is actually 40%, not 25%.

DNA testing allows us to test for carriers of mutations so that we can avoid this 25% risk of producing affected animals. But when all the dogs in the population are closely related, the average inbreeding of a litter is 40%, far above the 25% risk you're trying to avoid. You can see from this that health testing in Cavaliers is really not accomplishing anything except costing you money.

The problem with science is that it's true even when it's not what you would like to believe. The data for Cavaliers are clear. No amount of selective breeding is going to improve the health of this breed. You might temporarily reduce the incidence of some specific nasty mutation temporarily in a part of the population, but everybody is in the same genetic pot.

Inbreeding will continue to go up over time, the small genetic differences between populations will disappear over time as genetic diversity declines, and eventually you will no longer be able to produce healthy animals. In fact, this is where Cavaliers appear to be now.

Cavaliers are in deep trouble. There are plenty of other breeds in similar shape, but what matters to those that love Cavaliers is whether it can be saved. We know that we can only restore health by restoring genetic diversity. We do know how to do with without losing breed type. Animal breeders have been doing this for hundreds of years to produce quality animals that can be nearly identical, with inbreeding levels in the single digits.

It can just as easily be done for dogs as well, and Cavaliers are a perfect candidate. But not in a closed gene pool. I have to say that what I have read on social media this week makes me worry that breeders will continue to argue about the arrangement of the deck chairs while the ship slowly slips under the waves. I hope I'm wrong.

Carol Beuchat Scientific Director

Institute of Canine Biology USA.

REFERENCES Dreger, DL et al, 2016. Whole-genome sequence, SNP chips and pedigree structure: building demographic profiles in domestic dog breeds to optimize genetic-trait mapping. Disease Models & Mechanisms 9(12): 1445-1460. https://doi.org/10.1242/dmm.027037 Bannasch E et al 2021. The effect of inbreeding, body size and morphology.

TRUE? OR FALSE?

Puppies from a breed cross will have the health problems of both breeds: True? Or False?
The Institute of Canine Biology

By Carol Beuchat PhD

I keep seeing the statement in the title, usually in the context of a discussion about the need to improve genetic diversity of a breed with a cross-breeding program.
The people that say this, reveal their poor understanding of some basic principles of genetics that should be elementary level stuff for every dog breeder. But apparently not.

This statement is false, and here's why.

Most of the hundreds of genetic disorders identified in dogs are caused by single, recessive mutations.

A dog with one copy of the normal allele and one copy of the mutation will usually be unaffected and healthy. A dog that inherits two copies of the mutation will not, of course, have a copy of the normal allele, so whatever that gene is supposed to do in the body isn't going to happen. It will either be apparent as a disorder of some sort, or it will not be evident at all if the effects are subtle or do something like reduce fertility, or slow down some enzymatic reaction, or slow growth rate.

But apparent or not, it can be expected that if a dog gets two copies of a mutation, there will be some sort of functional deficit. Of course, not all mutations are recessive, but problems caused by dominant genes are easily managed by removing the carrier from the breeding population. The action of a gene can also be affected by the mix of genes in the genome of that particular dog (i.e., polygenic). How these genes affect the health of a dog can be complex and unpredictable, but in dogs polygenic disorders are far outnumbered by the problems caused by simple recessives.

So, let's just consider the case of the simple recessive mutation. Most breeds do not share mutations (Donner et al 2018). That is, mutations tend to be breed specific either due to founder effect or because they occurred after a breed split away from the ancestral dogs from which it was developed. A dog of breed A might be homozygous and affected by a recessive mutation, but when crossed to breed B will likely produce offspring that are heterozygous. Because of this, the offspring will not be affected by the disease.

In fact, the puppies produced by a cross breeding should be expected to be unaffected by any of the disorders of either parent that are caused by recessive mutations. This of course assumes that the two breeds being crossed are not so closely related that they could share some mutations because of a common origin.

Picture A "borgi", offspring of a Corgi x Boxer cross. (Cattanach) Now, the offspring of Breed A x Breed B will inherit some of the mutations of both parent breeds. Doesn't this make the offspring worse off than the parents if it carries mutations from both parents?

Remember that recessive mutations are only expressed if an animal inherits two copies. The way to prevent mutations from becoming a problem, regardless of origin, is to breed in a way that keeps the risk of a puppy inheriting two copies as low as possible. What does that mean? Related dogs will share some mutations, and the closer the relationship, the more mutations could be shared. To avoid the risk of producing affected puppies, just avoid breeding closely related dogs.

You might say that we can do DNA tests to avoid this problem, but in fact we can't. We can only test for the mutations that we know about and have a test for. What about all those other mutations lurking in the dogs that we can't detect? The risk of problems from them is also proportional to the relatedness of the parents. If you have DNA tests for both parents and they do not share mutations, you nevertheless embrace a risk of producing a genetic disorder if the sire and dam are related.

If you want to avoid problems from recessive mutations, don't breed closely related dogs. The fact that different breeds rarely share the same mutations is also the reason why mixed breed dogs are, on average, healthier than purebred dogs.

While they might carry more mutations, those mutations are much less likely to be homozygous and therefore be expressed as disease (Donner et al 2018).

The offspring of a cross breeding will produce offspring that will carry some of those mutations.

If those dogs do lots of breeding, they will produce many copies of those mutations packaged in puppies that will enter the breeding population. The way to keep those mutations from being a problem, is to not make hundreds of copies and distribute them throughout the population.

Keep them few and rare by nixing those popular sires. The answer to the question in the title is "false". Make sure you understand the explanations, and next time somebody makes this claim, call them out.

The statement is usually made to derail a discussion about how breeders should deal with high levels of inbreeding in their breed. Definitely you should have the discussion, but make sure everybody is armed with facts and a decent understanding of the relevant genetics.

For that matter, tackle the folks that claim that mixed breed dogs are not - and should not be - healthier than purebreds. If we get rid of all the problems caused by recessive mutations, then maybe. But in fact, from the simple facts of genetics, mixed breed dogs are less likely to suffer from disorders caused by recessive mutations than purebreds.

Believe in genetics; the world will make so much more sense.

https://www.instituteofcaninebiology.org/blog/puppies-from-a-breed-cross-will-have-the-health-problems-of-both-breeds-t-or-f

The Norwegian Ban on Breeding Cavalier King Charles Spaniels

– Cavalier Matters

07th Feb 2022 Norweigan Ban on Breeding Cavaliers & Bulldogs.
This announcement of the results of the court case in Norway has generated an enormous amount of discussion and outpouring of emotions on all sides. We all adore our Cavalier King Charles Spaniels and do not wish to see a ban on breeding in the future in the UK and internationally.

This decision means because of the severe health problems they may no longer be bred in Norway as ‘pure’ breeds. However they may be crossed with another breed in a scientifically controlled way with the aim of breeding for health. Part of our role as a charity is to offer support and advice to the many owners whose Cavaliers have serious health issues, (these includes Cavaliers from Puppy Farms and top show kennels) – often at a very young age.

In addition we have cared for many Cavaliers ourselves with these devastating conditions and had our hearts broken over and over again. Cavaliers are such an amazing breed and truly deserve the chance to live long, healthy lives – we need to find a way to make this happen.

The Companion Spaniel Project The Companion Spaniel Project Although there are many health focused, responsible breeders doing their best, there are not enough – sadly voluntary schemes have not been well supported over the decades so there has to be stronger laws around breeding and health testing. We need to keep campaigning for that and also encourage everyone to take responsibility to support those breeders fully health testing adults and puppies [at the appropriate ages] by ONLY purchasing puppies from them.

The Companion Spaniel Project is a good example of what can be achieved. Their aim is to produce healthy spaniels with improved head conformation eliminating CM/SM and early onset of MVD. After 5 years of careful selection and health testing the 2nd litter has just celebrated their 2nd birthday, it is still early days but so far the project has proved to be successful and the third generation is being planned.

The Companion Spaniel Project The Companion Spaniel Project Carol Beuchat of The Institute of Canine Biology has written an excellent blog on the subject: “This is not an attack on breeders. It simply applies existing law to a group of animals, purebred dogs, that have been flying under the radar of animal welfare legislation. If there were no welfare issues for these two breeds – i.e., that the dogs being produced can be expected to be healthy and not suffer from serious or systematic health issues that could cause pain and suffering – there would have been a different outcome”… “It is not the beginning of an indiscriminate attack on all breeds. It is, however, a test case based on two breeds that makes it clear that the existing welfare laws in Norway apply to dogs just as they do to other animals. Everybody must abide by these laws because they protect the welfare of animals.

WELCOME TO NEW DAY SPANIELS

Cavaliers are in Trouble - The Institute of Canine Biology

The Norwegian Ban on Breeding Cavalier King Charles Spaniels

– Cavalier Matters