Don't Throw The Baby Out With The Bathwater!
Dear Puppy Buyer...Hello again! Hope your year is motoring along ok. Today I want to explain a bit about how breeders should use genetic tests and why carriers of genetic diseases are still important in breeding programs.
I am in some support groups for different issues that come up with dogs. Not because I need the support but because I want to keep a finger on the pulse of those dealing with some diseases. Many of the folks in those groups are people like you...*just* pet owners. Folks who love their dog and their breed very much. Folks with hearts breaking as they watch their dog go through whatever it may be that they are affected by. Some of these issues present themselves at ages beyond breeding age, so there are times that breeders have rehomed these dogs and never experience the issue first hand. Some of these dogs were bred by folks who do not test.
Whatever the reason that we have to have these support groups, one common feeling rings loud from folks reacting on emotion alone...never breed a carrier of this disease!
This is a very emotional and very dangerous reaction for the breed. Here is why. You cannot just breed away from a single trait. Every gene affects numerous traits...not just one. If you focus on breeding away from only one thing and do not take into consideration the entire picture, you lose things that you cannot get back. Some of those things are part of the breed standard. Some of those things are temperament related. Some of those things are fertility related. The list goes on and on. Once those things are successfully bred out of a breed, they do not just magically come back. Once it is gone, it is gone.
So, what does this mean? This means that the isolation of the specific gene mutation causing an issue led to the creation of a test that breeders should be using as one tool in their breeding toolbox. Not the sole decision making factor...but a consideration. If a breeder has a dog that is a great example of the breed standard, but tests as a carrier for a recessive trait, the breeder has a tool to use when making a breeding plan. A carrier can be bred to a normal dog (or a dog not carrying any copies of the mutated gene) and not produce an affected dog. The puppies in that litter may all be carriers themselves...or they may all be normal...or any combination in between, but not an affected. There is no possible way for the puppy to have two copies of the mutated genes when there are 3 normal copies and only 1 mutated copy between the parents. This means that any of the puppies to be used as breeding animals need to also now be tested so that the owner/breeder knows the animal's status for this disease.
What if the pups are all carriers? That is ok!!! The breeder can breed their keeper to another normal animal in the quest to improve the structure as well as end up with the breeding specimens eventually ending up normal. We saw this emotional knee jerk response happen within my breed when we got the test for Primary Lens Luxation. Many breeders were shocked to find how many carriers they had and some of them panicked about it...made the decision to remove every carrier from their breeding program. They threw the baby out with the bathwater. As a result, they also lost all of the positives that those dogs brought to their lines. Instead, what breeders should be doing is simply using that information to make their breeding plan. If there are two dogs that compliment each other in every way, but one is a carrier and the other is normal, there is nothing wrong with making that cross. At all. In fact, if that is the case, it is a good idea to do it. But this means that the litter must be tested. That is the caveat. Thankfully, most of the things we have the mutated genes isolated for are pretty easy tests. Many of them have simple cheek swab tests that can be done at home, without a vet.
We need only look to the Basenji breed to see how the mindset of eliminating all carriers can devastate a breed. In the 1970's, Basenji breeders were on a mission to eliminate a fatal, but recessive disease called pyruvate kinase deficient hemolytic anemia (HA). While they drastically reduced the incidence of HA, the cases of Progressive Retinal Atrophy and Faconi's significantly increased. So...their passion to eradicate one fatal disease actually increased the frequency of two other issues...one of which being fatal and the other leading to blindness. They culled with such abandon that they eventually had to go to AKC to have stud books opened up in order to allow animals be imported from Africa and provide some genetic diversity. They had culled themselves into a bottleneck.
Some of these diseases are horrible...heartbreaking...painful...and if you have a pet that you love that is suffering or has suffered from it, it is very easy to see why your instinct would be to not understand why any breeder would ever breed to a carrier. But preservation breeders know that these tests allow us to keep genetic diversity and desirable traits while still breeding away from the disease. Many breeders realize that focusing only on eradicating one disease leaves you open for having a problem with another...as many of the carriers for Disease 1 are normal for Disease 2 and even Diseases 3 and 4. Eventually, yes...the goal would be to breed it completely out and have every animal test normal...but the knee jerk reaction of removing every carrier is not a reasonable or healthy decision to make.
If you have made it this far and are interested, here is a very good article about what happened when the Basenji breeders opted to cull with wild abandon as well as a little more in depth discussion on why our carriers are valuable to our breeding programs. Thankfully, the Basenji folks were able to correct the damage that had done.