Knockout Chihuahuas

My Canine DNA Testing Journey

By KRISTI GREEN·THURSDAY, AUGUST 6, 2020

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DNA testing breeding animals is nothing new, however it has recently risen in popularity as availability is better and the tests are more and more accurate. I wasn’t totally sure I was on board with the concept of DNA testing my dogs for a bunch of stuff they probably didn’t carry as it was expensive. It also seemed that the overwhelming majority of chihuahuas tested so far had pretty uneventful reports. I watched others do DNA tests for a few years before deciding to take the plunge.

After exploring various options I decided to order the Breeder DNA test kits from Embark. These kits screens for over 190 various genetic disorders, with 7 of those tests being specifically identified in my own breed. These test kits also give basic color and trait information possessed by each dog tested along with genetic coefficients of inbreeding. To date I have done 25 dogs including several dogs who were already retired from my breeding program but were dogs whom I considered very influential and appeared in multiple pedigrees for my program.

I’ll be honest – a small part of me didn’t really WANT to test all of my dogs because what if someone came back as affected or carrying something horrible? I think this feeling combined with cost is probably what holds a lot of people back from testing their breeding stock via DNA.

…Plus, its REALLY easy to assume that one’s dogs are fine because they look fine…right?

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Overall the first few results that came back were pretty unremarkable. I started to feel like it was maybe a little silly because why am I spending all this money if everyone is fine?

Then…the first “INTERESTING” result came back.

One of my young stud dogs is a carrier of 1 variant for Progressive Retinal Atrophy - crd4/cord1 carrier.

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Whoa. WHAT?

Being that he is a carrier of only 1 variant, he himself will never develop the disease. However if he were to be bred to another carrier there is roughly a 25% chance that puppies produced could be “affected”. PRA is pretty serious as it ultimately causes a dog to go blind and often at a very young age. Now, THAT is some remarkable stuff, and DEFINITELY information I want to know when choosing breeding pairs!

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The first thing I did was I let anyone who had used the dog know that he carried this gene and advised them to test their keeper puppies. Then I pulled up his pedigree and tried to figure out where it may have come from. About ¾ of the pedigree had already been DNA tested clear/non carriers for the disease, but the last ¼ I really wasn’t quite sure where it might have come from.

Several more dog’s results came back. All unremarkable. Everyone CLEAR.

Then… a second dog, this time a bitch (who was already retired from my program but an ROM dam), came back as a carrier for Progressive Retinal Atrophy - crd4/cord1. The second her results came back I got a much clearer picture of where it was coming from. Her dam was DNA clear, so I knew it had to be her sire that she inherited the gene from. And…her sire is also the great, great, great grandsire of the first dog who was came back as a carrier -- AND he was in the only quadrant of his pedigree that I couldn’t confirm was clear by DNA.

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Again I advised anyone who has breeding dogs out of this particular dam to DNA test for this variant. I also explained that if their dog carries PRA crd4-cord1, it just means they should test the potential mating partner to ensure a CLEAR status. In addition, puppies resulting from matings out of carriers should be tested if they are to be bred.

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The good news? So far the two daughters of the carrier bitch who I have tested came back clear. They do NOT carry the gene for PRA crd4-cord1. Yeah!

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So wait, why aren’t we just eliminating these carrier dogs?

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It’s important to understand that carriers do NOT pass their carrier status to all of their offspring... AND...removing carriers can dramatically hurt genetic diversity. Genetic diversity is incredibly important and is hugely responsible for the overall wellbeing of a given breed. Our gene pool is already fairly small. As a result, we shouldn’t remove carriers…we just need to know who they are and be sure they are bred to dogs who are CLEAR.

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The bad news? It (genes) can just hang around. The young stud who is a carrier? It just…hung around . For FOUR generations and directly links back to the same dog as the other carrier I have...and no one was any the wiser. There are hundreds, maybe thousands of potential carrier dogs out there who are related to these dogs.

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It’s important to note that carriers for PRA and other issues may be completely normal on their physical health testing exams – both of mine were and have clear CAER/CERF exams.

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I’ve opted to make all DNA results public via my webpage along with all of the other health results for each dog. Anyone wanting to breed to this dog (or any dog) who is a carrier simply needs to DNA test their bitch at a minimum for that variant. He is a gorgeous sound dog who is producing beautiful puppies - it would be a huge loss to the breed to remove him from the gene pool. Responsible choices will prevent the loss of genetic diversity as well as aid breeders in avoiding ever producing affected dogs/puppies.

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Given my experience I want to encourage anyone who breeds their dogs to DNA test their dogs for things you can’t see. Genotype is not visible like phenotype is.

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You may be surprised what you learn, I **definitely** was!

I think in the chihuahua breed right now there are few dogs carrying much of anything…but that said, the two confirmed carriers I have for PRA CRD4-cord1 both go back to the same dog. At this time several other confirmed carriers have also come back also related to the same dog.

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It seems to me there are two paths –

Path 1 -- no one tests until people start getting affected dogs. Everyone assumes their dogs are fine and mine are magically the only carriers in the breed (I promise you, this is not the actual case)… At that point the problem will be MUCH bigger and MUCH harder to breed away from. This would be very sad…

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Or Path 2 -- we become aware now and we can avoid ever seeing affected dogs plague our breed. For me, I choose path 2, and will continue to use DNA testing to screen all of my breeding stock.

I feel we have an opportunity in our breed to head this off before we are bottle-necked into an issue like you see in so many other breeds. However if no one does or says anything about these results when we find them we get closer and closer to path 1 without even knowing it. That is why I am choosing to write this article even though I know some people will be nonreceptive or unkind as a result. Ultimately I care more about my breed than what feels comfortable.

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I think it is incredibly cool that we have these tools and can make more informed decisions in our breeding programs than ever before.

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I’m excited that in addition to regular health testing I have this added tool in my tool kit and I hope that other breeders who are on the fence may join me on the other side of the world that is DNA testing to protect and preserve the future of our precious breeds.

I believe that knowledge is power. One of my favorite sayings, “better the devil you know...” rings more true now than ever.

**PLEASE NOTE: Embark has no idea I wrote this article and the views expressed in this article are solely my own opinion and experience.

 

**I did do an additional DNA test for the specific variants found to verify/confirm the result from Embark was correct via VetGen. I feel confident that the results are correct.

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More Info on PRA:
https://embarkvet.com/products/dog-health/health-conditions/progressive-retinal-atrophy-crd4-cord1/

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More Info on Breeding Carrier Dogs:

http://www.animalabs.com/breeding-carriers-breeding-program/

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