Welcome to the era of health testings for dogs. Thanks to science, breeders can have their dogs screened for genetic mutations. Breeding without first doing the available health tests is considered as irresponsibility. The mantra of responsible breeders is to claim loud and clear that their puppies come from parents “fully screened” for the inherited diseases of the breed.
Screening for hereditary diseases is supposed to be an essential argument for the seriousness of the breeder.
But is this the best way to minimize the risk of hereditary disorders?
Health tests are generally used in the wrong way and we will see why.
The stud selection
We want to breed a female because she has qualities that we consider interesting for the breed. For this, we have selected five males. We have classified them according to their build and character. We have also taken into account other criterias that seem relevant to us. Ranking is done by a star rating system.
Screening for hereditary diseases
The first thing to do is to gather all stud health test results for known recessive mutations in the breed.
We also have the official reading result for hips and elbows dysplasia as well as the eyes examination result for progressive retinal atrophy (PRA).
We now have our “health tested” studs. Among them, we will have to select the perfect male for our lady. But also, we need to provide a plan B in case the mating with the chosen male does not work as planned.
Select the best possible combination
Dog health test results show that male #2 carries the degenerative myelopathy mutation. Our female also carries the same mutation. Their combination would produce 25% of puppies homozygous for the gene responsible for this disease. We therefore choose to remove this male from our list. Thus, we have reduced the risk of producing affected puppies from 25% to 0%.
Looking at the tests results for hereditary diseases as well as our system of studs rating, we decided to select the male n°1 for our breeding project. Male n°4 is kept in plan B. Another breeder might have made a different choice elsewhere. Like any selection, there is always a subjective part in the hierarchy of criteria used to select.
Heats arrive and it is necessary to make the long trip to the male who is in a foreign country. The mating works and two months later our female dog produces a beautiful litter of puppies. These are presented as they should be from all angles with pretty photos, each as beautiful as the other. These photos are published on our breeder website and on social medias.
We of course proudly announce that our puppies come from fully health tested parents. A breeding selection applies to one of the puppies for our breeding program. Then we place the rest of the litter with loving families.
Problems are coming
Some time later, one of the puppies owner contact us. He informs us that his dog suffers from a serious hereditary blood disorder. He asks us how is this possible? Indeed, we told him that as a responsible breeder, our puppies come from fully screened parents! So how is this possible?
With health tests we only know what we can know
We can only know if a dog has a mutation if we have a test for it! We have done all available health tests to find out the status of known recessive mutations for the parents. But dogs have many recessive mutations lurking into their genome. Unfortunately, there are no health tests available for these. We had no way of knowing if these recessive mutations are present until they rise.
Obviously, there was a mutation in our parents that we didn’t know about. We feel bad. We offer mediation solutions to our adopter. Then we dive back into the pedigrees to understand what could have happened. How could we have produced a puppy with a genetic disease after being so careful? All health tests for hereditary diseases had however been carried out.
It is impossible to know the recessive mutations that hide in your lines if you have no means of detecting them!
If there is no health test for a recessive mutation, a disease can suddenly appear out of the blue. Including within its own lines as long as two carriers are coupled. That’s why if a breeder claims he only breeds with his own lines because he “knows what’s in his lines”, now you know he either doesn’t understand genetics, or he is dishonest.
Avoid stepping on mines!
Well, that’s all very well, but it leads us into a dead end. All dogs have recessive mutations and there will always be some that we will never know about. So how do you find the means to avoid them?
It’s like going through a minefield where there are three mines you cannot see (but flagged to you) and another 37 mines lurking somewhere. One wrong step and you will meet your creator. If the three mines reported are the recessive mutations that we have health tests for and the other 37 mines are unknown recessive mutations lurking in the dog’s genome, it’s a risky way to do reproduction, don’t you think?
Good breeding practices to limit the risk of genetic mutations
And now imagine there is a second minefield. You have the choice to go through one of the two.
The first field therefore contains three mines that you know and can be avoided. But 37 other mines are hidden there.
The second field also has three reported mines but only seven others are hidden. If you want to reduce the risks of stepping on a mine, you will logically decide to cross the second field. Indeed, the risk of blowing oneself up there is only 20% of the risk of the first minefield..
How does this apply to dog breeding? Let’s pull back the curtain and reveal the invisible mutations in the dogs in our breeding program. These unknown recessive mutations have no health tests available.
Now we can see the problem. Our female dog has not one but three mutations that are also found in some of our studs who were nevertheless “entirely health tested”. Now that we can see these other mutations, we realize that our selection of the male #1 turned out to be a very bad choice…
Great, you say. But in the real world, if we don’t have tests for these unknown mutations, then there’s no way to avoid them, right?
The inbreeding coefficient
In fact, there is one: the estimated inbreeding coefficient of the litter. Remember that inbreeding is defined as the probability of inheriting two copies of the same allele at a random locus on the chromosome. By definition, inbreeding is therefore homozygosity. If a litter inbreeding coefficient is 25%, the probability of inheriting two copies of the same allele is 25%. If that allele happens to be a deletarious recessive mutation, the risk of producing a genetic disorder caused by that recessive mutation is also 25%. Similarly, if the inbreeding rcoefficient is 10%, the risk of a genetic disorder produced by a recessive mutation is also 10%.
For our stud selection, we carried out health tests for hereditary diseases to eliminate the 25% risk of producing a recessive genetic disorder for a known mutation: degenerative myelopathy. But we just explained that the estimated inbreeding coefficient of the litter would have told us the risk of producing a genetic disorder from ANY recessive mutation; the ones we know AND the ones we don’t know.
We can act on the genetic disease risk of all recessive mutations using the litter estimated inbreeding coefficient.
And if we had to do it again ?
Let’s go back to our studs list and add a line to show the litter estimated inbreeding coefficient for each combination.
If we are testing for degenerative myelopathy and eliminating carrier studs, it would be counterproductive to select the male #1 given the 40% litter estimated inbreeding coefficient… We paid for health testing for dogs to eliminate the 25% risk of the known mutation, then we did a combination with a 40% risk of producing an inherited disorder from another mutation that we don’t know…
Wait… Let’s read that again!
We tested and eliminated carrier studs so there was no chance of producing puppies affected by the known mutation, then we combined with a “healthy” stud for a 40% chance of producing puppies with a disorder of another mutation that we don’t know…
Hello Houston! We got a problem!
Genetic disorders risks are linked to inbreeding coefficient.
Conclusion
All these health tests are a waste of time and money if we choose parents who produce a litter with a 40% inbreeding coefficient. This is the wrong way to use health tests for dogs. The breeder believes he has done everything to produce puppies that will live long and healthy lives thanks to screenings for hereditary diseases. But in fact, he is reporting mines with flags in his field. Then, he assumes that the latter is secure without taking into account the risk produced by the many other mines that have remained invisible and that he himself helped to disseminate.
To produce healthy dogs, we must minimize the risk of problems caused by ALL recessive mutations. The ones we know AND the ones we don’t know.
EMBARK genetic inbreeding coefficient helps to decrease genetic mutations risk.
You can estimate this risk from the litter estimated genetic inbreeding coefficient given by Embark. Indeed, you can submit to Embark a list of studs that you have selected for your marriage project. Of course, these studs must first have been genotyped at Embark.
It is useless to invest money in health tests for dogs while continuing to produce litters with a high inbreeding coefficient…
All known health tests should be used to rule out the risks of mutations that we know of. But it is also necessary to use the litter inbreeding coefficient and preferably, to use the coefficient established from data derived from DNA, such as those of Embark because the data derived from pedigrees is not reliable… Thus by carrying out these two inseparable steps, we make sure to reduce as much as possible the risk of unknown mutations lurking in the genome of each dog. This is the best way to minimize the risk of recessive diseases.
A responsible breeder should ensure that he has eliminated all risk of known recessive mutations using all available health tests for dogs AND have minimized the risk of producing puppies with unknown recessive mutations by selecting a combination that will produce a litter with the lowest possible inbreeding coefficient.
Sources :
- Institute of Canine Biology
- OMIA – Online Mendelian Inheritance in Animals
- OFA – Orthopedic Foundation for Animals
- IPFD – International Partnership for Dogs