Inheritance patterns for breeders
Jenna Dockweiler, MS DVM, DACT, CCRT, CVAT, and Lindsey Kock, DVM, explain how DNA testing impacts breeders.
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Adam Christman, DVM, MBA: Share with me a couple of cases that you want to share with the audience.
Jenna Dockweiler, MS, DVM, DACT, CCRT, CVAT: So actually one very cool case for me as a theriogenologist, which going back to the if we can't read a swab for any reason. We had a little husky. She was about 17 months old at the time that her owner ordered her first test and essentially, her genotyping ended up failing three times. If there is another dog's sample within that DNA sample, so like if there's a duplicate sample, it gets contaminated with another dog, the machine just won't read. So after the third one, we looked more deeply into it. We found that there were actually two distinct DNA signatures within that sample, one of which had an XX karyotype, so female, and one of which had an XY karyotype, so male.
Looking back at this patient, she kind of had what I would consider to be a doggie appearance like a broad skull, bigger in stature than her littermate sister, and had never gone into heat, although her littermate sister had cycled twice already. So very likely that she's an XXXY chimera. What chimerism is, is when two little embryos kind of stick together very early in only a few cell stages of development, and then develop into one single dog. It's not very well understood in dogs. It's not very common, but there are no known health complications associated with chimerism beyond the reproductive consequences.
Unfortunately for this little girl, her owner was pursuing DNA testing as part of a responsible breeding program, which of course is likely not going to be her fate ultimately. But at least we had an answer for her as to why she was wasn't cycling. So we probably saved her a pretty expensive primary anestrous workup.
Adam Christman, DVM, MBA: Wow, that's fascinating. Wow, that's really wild.
Lindsey Kock, DVM: I think that brings up an interesting point. We've talked about education on results with clients in the exam room and in looking at, depending on who you're talking to, right, I think results can be a lot more straightforward for a pet that's been spayed or neutered. But if you have a breeder come in and want to go through results, I think the first thing I would do is change that 15-minute appointment to 30 because, going through a Punnett square, doing a little biology lesson, and going through the basics of inheritance and what that means, is so important for our clients who are breeders. Especially with breeds where there's maybe less of a pool to choose from, so to speak.
When issues pop up or there are variations in the DNA, it doesn't mean necessarily that they aren't candidates for breeding, but it means that they probably need some assistance in interpreting those results and making some smart breeding decisions. In those more in-depth cases that come up, I think those are really interesting, but can be fun to work through, but take a little bit more time, too.
Adam Christman, DVM, MBA: Let's talk more about that, actually, with breeders, 'cause I think this is a fantastic discussion we're going with. With breeders and DNA testing, where have we been with that? 'Cause I know DNA testing has not been around that long ago, so where are we at this day and age with it?
Jenna Dockweiler, MS, DVM, DACT, CCRT, CVAT: Breeders have actually been using DNA testing probably longer than the pet owning population has. So kind of the two halves of genetic screening, if you will, are testing a population that is at risk for a disease and seeing who might pass those disease alleles on to the next offspring. So, breeders have been using sort of that second half of the definition for quite some time now.
Like Dr. Kock said, it doesn't necessarily mean that you can't use your dog in a breeding program if they do come up with a genetic risk. It just means that we have to pair smartly to avoid producing at-risk puppies. And actually, my own dog is an example of this. She is a factor seven carrier, so that is a recessive disease, meaning that she would need two copies in order to be at risk for excessive bleeding. She's only got one copy, but I can't breed her to a boyfriend who's got one or two copies, because doing so would potentially produce at-risk puppies. And as a responsible breeder, I'm not willing to do that. You just have to be a little bit smarter about who you're choosing to breed to.
Adam Christman, DVM, MBA: What is that conversation like when you get the results back as a veterinarian to the breeder when you're going over the results? What next?
Jenna Dockweiler, MS, DVM, DACT, CCRT, CVAT: I would say that most breeders are fairly savvy with genetics. Most of the good breeders are fairly savvy with genetics, but again, just putting it out there right at the outset that this doesn't mean that your dog can't be bred. Even dogs who are at risk for genetic conditions can sometimes in some circumstances be responsibly bred if they're paired smartly and if the breeding is not expected to exacerbate their condition. Because of course they are our primary patient rather than the potential litter. I think that putting that at the outset because some breeders can be very upset even if they have a carrier result but say hey this doesn't eliminate your dog from the breeding pool we just need to be smart about this.
Adam Christman, DVM, MBA: How important is it to you when you're hearing this information about understanding genetics and with breeders that we're doing more responsible breeding?
Lindsey Kock, DVM: I have found that for each breed of dogs or cats—we’re not talking about cats today, but cats too—that there's an individual language with that breed. I think that's always the really interesting thing to learn is I always start that conversation with, "Tell me about your breeding program.”
Breeders love to talk about physical traits too which as a veterinarian is sometimes, to be honest, hard to wrap my mind around the genetics of those physical traits. Coat colors can be really complex, but breeders have this whole real life knowledge of what that means. I think the best conversation and the best relationship is when I can listen to them coming into the exam room to talk about their experience, to talk about what they have physically seen, and come to that with the perspective of the actual science of genetics, right? That's when we can meet in the middle, and we can have that conversation about, yes, I know that this genetic variant is something that's been a concern within your breed. And that this might be a little bit scary for you, but let's look into the science of how the inheritance works and kind of walk through, this is a genetic recessive trait, right? Doesn't mean that your dog is at risk for having this clinical disorder, it just means we have to choose the right mate for this dog. Coming to it as a partnership, it makes such a big difference in the success and in the care for those animals.
Adam Christman, DVM, MBA: Yeah, a true partnership.
