Danika Bannasch, DVM, PhD: Chondrodystrophy

Helpful Definitions

chondrodystrophy (CDDY) – a genetic mutation that causes abnormal vertebral discs with premature degeneration and slightly shortened legs in dogs. This mutation increases the risk of back pain, including but not limited to intervertebral disc herniation, which can lead to significant pain and loss of mobility. Dogs with this mutation have intervertebral disc disease, and can have back pain whether or not they actually have intervertebral disc herniation.

chondrodysplasia (CDPA) – a genetic mutation that causes abnormally shortened, often bowed legs in dogs. This form of dwarfism is not associated with intervertebral disc disease. 

skeletal dysplasia – a general term for other dwarfism phenotypes that may be found in different dog breeds. These could affect breed morphology and health in a variety of ways.

intervertebral discs – the cushions that occur between the vertebral bodies (vertebrae) in the back. These allow the spine to be flexible, and act as shock absorbers.

intervertebral disc disease (IVDD) – abnormal intervertebral discs that cause some level of pain and discomfort, and are more likely to herniate.

intervertebral disc herniation – when a vertebral disc ruptures and some of the softer inside part pushes out into areas where it isn’t supposed to be, damaging the disc and surrounding tissue. This causes pain, and can lead to paralysis if the disc hits the spinal cord. 

heterozygote – the individual has one copy of a variant gene. In CDDY, this dog would have one normal gene and one CDDY gene, written as n/CDDY.

homozygote – the individual has two chromosomes of a variant gene. In CDDY, this dog would have two CDDY genes, written as CDDY/CDDY.

phenotype – the physical manifestation of an individual’s genetic structure. For example, the phenotype of a dog with CDDY would be slightly shorter legs and abnormal vertebral discs.

genotype – the genetic structure behind the phenotype. For the CDDY gene, a normal dog would be written as n/n, and a dog with CDDY would be n/CDDY or CDDY/CDDY

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[Upbeat music intro]

Jessica Hekman: Welcome to the Functional Breeding Podcast. I’m Jessica Hekman and I’m here interviewing folks about how to breed dogs for function and for health; behavioral and physical. This podcast is brought to you by the Functional Dog Collaborative, an organization founded to support the ethical breeding of healthy behaviorally sound dogs. The FDC’s goals include providing educational, social and technical resources to breeders of both purebred and mixed breed dogs. You can find out more at functionalbreeding.org, or at the Functional Breeding Facebook group, which we work hard to keep friendly and inclusive. I hope you have fun and learn something.

0:47

Jessica Hekman: Danika Bannasch, DVM, PhD, is the owner of Pint, the famous UC Davis football tee retrieving dog. She also happens to run a genetics lab, also at UC Davis, where she studies the genetics of inherited diseases in dogs and other animals. She’s known for her work associating genetic variants with a variety of traits, including coat color and skull shape. In this episode we’re talking about a genetic mutation that she discovered, known to genetic testing companies as CDDY, for a trait that she feels passionately about – chondrodystrophy. Most of the dog world knows this mutation as ‘that risk gene that makes your dog more likely to get IVDD’. But in this episode, Danika talks us through the difference between IVDD, actual disc herniation, and the back pain that all dogs with this mutation suffer. I hope you learn as much from this discussion as I did. 

JH: Hello, Danika and welcome to the podcast! I’m so happy to have you here.

Danika Bannasch: Thank you so much, Jessica. I’m happy to be here. 

JH: So I always start out by asking people to tell us about their dogs and I bet you have a few.

DB: I only have five right now. 

JH: Only?

DB: Yeah, my farm is called Five Dog Farm. So that tends to be the hard limit that we get to, but every once in a while there’s a sixth. I have two Nova Scotia Duck Tolling Retrievers. Pint is 13, he just turned 13, and Ritz is eight years old. And then I have three Danish-Swedish Farmdogs. So Cricket is my oldest, and she’s… I didn’t really say what I do with the two Tollers. They’re sort of retired now, but they did hunt tests and agility and conformation. And then Cricket the Farmdog is my competitive agility dog. She’s awesome, she’s fantastic. I love competing with her and playing with her. And I have a daughter of hers whose name is Taq, T-A-Q, which is a science geeky name that I got to give her, and a middle Farmdog there who is Juice and she is a tracking dog.

JH: Very fun. 

DB: [unintelligible] Barn Hunt. And so I compete in AKC.

JH: And you have bred in the past or do you breed now? Is that behind you? Or is that still something you do? 

DB: Yup, yup. I’ve been a Toller breeder for many years. And I’ve been breeding Farmdogs for a couple of years. 

JH: Excellent. All right.

DB: So I bred Taq and kept her. And I bred Pint.

3:22

JH: Excellent. All right. And you are a researcher at UC Davis, can you just sort of give us general guidelines of what kinds of – general outlines – what kind of stuff you study so that people are oriented to where you’re coming from? What are your research interests? 

DB: Sure. Yeah. So I study inherited diseases in dogs. I will say I have a, you know, ‘secret not so secret’ passion for color genetics. So on the side, I do a little bit of coat color genetics. During my sabbatical I did a coat color genetics project, which was super fun. But most of the time I try to concentrate on inherited diseases that affect the health of animals. So my lab works to identify what the genes and mutations are that causes diseases, and that gets translated into tests. Commercial tests that people use to test their dogs for breeding purposes. And then I do a lot of counseling, and I educate vet students about genetics and inherited diseases. 

JH: That’s so important. A lot of times people will ask me, “How do I know how to interpret this genetic tests that I got back?”, and you really want to be able to say “Go to your veterinarian.”, and yet I always really hesitate to say it. So I graduated vet school in 2012, and we had no genetic testing. I mean, Embark wasn’t a thing yet then, right? Like it was just, I had no education on that. And I certainly know how to do it now. But the average vet does not. So. 

DB: No they don’t, and even with the little bit of education that we give them, I think that they’re mostly not super comfortable with it, but at least they have some exposure. And maybe that helps them know what they know and what they don’t know. 

JH: Yeah, knowing what they don’t know is probably the most important tool you can give them. 

DB: It’s pretty funny in the state of California because I’ll run into people in an agility trial, and they’re like, “Hey, my vet says that you were their teacher!” and I’m like, “Yeah, yeah, it was all of the vets.”. Because I’ve been doing this for 23 years now, so now I’ve pretty much covered all of them.

5:32

JH: Yeah, sometimes I feel similarly that a lot of dog trainers out there have had classes with me, but I can’t say that I’ve trained all of the dog trainers in a particular state. So speaking of genetic tests, that is what we are here to talk about, and to talk about the relationship between short legs and spinal disease. So why don’t we just start out by talking about what we mean, when we talk about dogs that have short legs? Can you just give us, you know, what kind of phenotype are we talking about there? 

DB: Sure. So, I mean, I’ll tell you that there’s lots of different variants that are known that can cause short legs in dogs. And I think people kind of classically see a dachshund or basset hound and, you know, it’s pretty clear that they have short legs. You can ask me about long backs later, but it’s a pet peeve of mine. They have short legs, they don’t have long backs. So those are super short-legged dogs, and we understand more about why they have short legs, but then there’s kind of dogs in this intermediate type like cocker spaniels and beagles that also have short legs but it’s pretty subtle. And chondrodystrophy and chondrodysplasia are two terms that have been used to describe short legs in dogs. And we can kind of talk about where those come from and what the definitions are. But chondrodystrophy was originally described in the 1950s by Hansen, who, along with other veterinarians had noticed that there were some dogs that would become spontaneously paralyzed, and they wanted to understand why this was. And so he looked at a set of dog breeds, he analyzed them histopathologically. So these were animals that had died for other reasons, he looked at their intervertebral discs, which is the cushions that occur between the vertebral bodies in the backs of the dogs. And he found that a certain set of dogs had abnormal discs from a very young age, and came up with this term chondrodystrophy. And so he thought that these disc abnormalities were what were predisposing them to their back problems. The interesting thing about what Hansen did is the set of breeds that he studied. So it was dachshunds, Pekingese, French bulldogs, and spaniels. And when I went back and was… and dachsbracke, which is a breed we don’t have in the US so people won’t have heard of them. But when I went back and looked at his papers I’m like, “Why doesn’t he say which spaniels?”, but he was actually correct because all spaniels have chondrodystrophy, so it was fine that he just said spaniels. And then later on Braund did work in the beagle and showed that the beagle was also a chondrodystrophic breed. So those breeds that I named are the ones that are considered chondrodystrophic, meaning that they have short legs, but not necessarily super short depending on which dog you’re talking about. And they have these disc problems. If we fast forward to the early 2000s, when Elaine Ostrander’s group identified a major cause for dwarfism in dogs, they use the term chondrodysplasia. So chondrodysplasia versus chondrodystrophy. And they phenotyped dogs by, you know, dogs with super short legs versus dogs without short legs, and they found this variant on chromosome 18, which was an fgf4 retrogene. And later on, when we identified a second fgf4 retrogene that was responsible for chondrodystrophy, it was really great that the Ostrander group had used the term chondrodysplasia because the chondrodystrophy name had been given to these dog breeds in the 1950s, so it wasn’t really up to us to change it. So it actually turned out all okay, as far as the way we refer to these things. I’ll just say that there are other dwarfism phenotypes that segregate within breeds and probably the more correct term for those is skeletal dysplasia. And so depending on what breed you have, you might have a mutation test for skeletal dysplasia 1 or 2. And even when we were working on chondrodystrophy, we were calling it skeletal dysplasia, because we didn’t know it was chondrodystrophy when we started. Did I completely muddy that?

JH: No, I was actually thinking what a great job you were doing of describing it. Because sometimes I have to interrupt researchers to be like, “Please explain that term.” But you did every term that I was like, “I’m gonna have to ask her to explain what the intervertebral disc is.” you would pause and be like, “Oh, this is what it is.” I think for all of those terms, it would be helpful for people just to have a visual, but we can’t do that on a podcast. 

DB: That’s right, that’s right. And I will say, just to be clear, this is not something that every veterinarian has clear in their minds either. And so that makes it really hard for people. I mean, I can still remember when the chondrodysplasia paper came out, and you know, my neurologist friends and I got together and I’m like, “This isn’t chondrodystrophy. These aren’t the right breeds. These aren’t the breeds that are herniating.” And so we sort of knew, like, well chondrodystrophy is still out there sitting somewhere. And this obviously is a major form of dwarfism, but we were confused at the time. We had to go back to Hansen’s work to figure out which dogs were chondrodystrophic. And there were even some papers where they decided that the way to define chondrodystrophic dog breeds was to just count how many times in the veterinary literature a breed had been referred to as chondrodystrophic. And I’m like, okay that just means there’s a lot of misunderstanding about the term and how it should be defined and how it was originally defined. 

JH: Yeah, that’s quite circular. 

DB: Certainly neurologists are really good on it, but everyone else, maybe not so much. So. 

11:39

JH: Yeah, for sure. I’m definitely struggling, myself. And I would hope that I would know better, but it’s, yeah, it’s not something that I was well versed on in vet school for sure. All right. And then the specific spinal disease that we’re talking about – intervertebral disc disease. Can you tell us a little bit about that, and what that looks like, and how serious it is? 

DB: Sure. So right off the bat, we need to define things again. So we covered chondrodystrophy and chondrodysplasia. IVDD stands for intervertebral disc disease, but often gets sort of used interchangeably with intervertebral disc herniation. And that’s a problem. So, the disease that Hansen studied led to all of the intervertebral discs being diseased, being abnormal. So for me, chondrodystrophy and IVDD are completely interchangeable. So a dog that has the chondrodystrophy variant has abnormal intervertebral discs. It can live its entire life with its abnormal intervertebral discs, and no one will ever really notice. It can also have bouts of back pain, and if one of those disks herniates in a certain way, it can smash into the spinal cord and cause compression and bleeding and damage. And that can lead to either severe acute pain or paralysis. Depending on where in the spinal cord at herniates, they can be paralyzed in all four limbs or just in the hind limbs. And we actually know now that dogs have herniated that don’t show clinical signs. So in other words, the disc didn’t smash dorsally up into the spinal cord, but it kind of went to the side. And I’m sure that dog felt pain, but not anything that the owner noticed. And it wasn’t in pain when we examined them, because we look at some of those. So I think that the ‘intervertebral disc disease’ versus ‘disc herniation’ is probably the biggest source of confusion. Because a lot of people will say, “Well, my dog is fine. It’s never had a disc herniation.” In other words, it’s never been acutely paralyzed. Of course, it probably has had some… it might have had a herniation event, but it never became paralyzed. “Therefore, this test isn’t relevant to me.” And just to put this in the context of people, I personally have back pain. You probably do too, pretty much everyone does when they get old enough. The amount of degeneration that is seen in chondrodystrophic dogs’ discs is way more than is probably in your back or my back. And yet I have back pain, and you probably have back pain, a lot of people have back pain. People rarely go so far as to herniate a disc. But even that level of degeneration would be pretty severe in a human. So it’s something that, you know, I think it’s hard for people to wrap their heads around that. I mean, you know, of course that dogs don’t talk, that they don’t complain about back pain. And so we don’t know that they’re in back pain. In fact, we always say in veterinary medicine, ‘apparent back pain’, because the dog can’t tell you it’s in back pain. It can bite you, it can scream, but it can’t say “My back hurts.” And so if their back hurts, and they’re not biting and screaming, then how do we know whether they’re in pain or not? So it’s apparent back pain. But anyway. 

JH: Yeah, I think that kind of thing can be really hard for owners to perceive. And that’s reasonable. We’re not trained as owners to perceive it. I found it really mind bending a couple of years ago to read a paper about the number of behavior problems in animals that were linked to pain, and to realize how often we may have a dog where we think what we’re having is a behavior problem, or the dog’s just getting old and slowing down, or he just doesn’t like getting on the couch anymore, and there’s actually something more going on. It’s really hard for us to believe that things are there that we can’t perceive, right? We really want to be able to see things and touch them before we can believe that they’re there.

DB: Yeah, and I think, you know, Sarah Stremming always says like, “It’s physical first.” and “Look for physical problems.”, and I mean, I just have to echo that. It’s so often physical and not behavioral. And we just, you know, they can’t talk to us. I look forward to the day that we have tracers that can tell us whether dogs have neurogenic pain, and so that we can test them and know that they’re in pain, even though they can’t tell us and then treat that pain. Because I mean, the idea that, you know, our beloved pets would be in some form of chronic pain and still working and still doing things for us just like, really bothers me.

JH: That we’re asking them to do things, and they’re doing it because they’re such good kids. Yeah. 

DB: Or that we’ve bred them to be…

JH: To be obsessed with the ball or whatever. Yes, yes. So I like that simultaneously saying that there’s the disc disease, which is important. Herniation is what we often perceive… herniation often leads to something that then we bring the dog into the vet and we get the MRI and we see it, but that the disease is something that we should be concerned about whether or not herniation has happened or whether or not we have perceived the herniation. Is that a fair summary?

DB: Yeah, and I mean, that’s my belief. That looking at how abnormal these discs are, that I can’t imagine that animals don’t have problems associated with that prior to a herniation event, or in addition to. Obviously, you know dogs that herniate can often herniate again, a different disc. And in fact, and I am not a neurosurgeon, but when they do surgery for a herniated disc they actually fenestrate the discs nearby so that they won’t herniate and slam into the spinal cord. And they wouldn’t do that if it wasn’t so common for them to herniate a different disc afterwards.

18:16 

JH: I remember that. I remember standing there, looking at the back of the resident’s scrubs, being told “Now they’re fenestrating the discs.”, and thinking, “Gosh, I bet that would be interesting if I could see it.” That’s what I remember. So then the next question is, how much does genetics play into – and let’s be careful about how I asked this question – how much does genetics play into the likelihood of getting the disease, plus or minus actually herniating? So how much of that is genetic risk? How much of that is environmental influence?

DB: So if the disease you’re talking about is this premature degeneration of the discs, as far as we know it’s 100%. I mean, Hansen’s predictions about which breeds have it completely correlate to which breeds have a really high allele frequency or are homozygous for chondrodystrophy. We’ve also done a study with a set of Tollers – 21 Tollers, so seven dogs of each of the three genotypes, and looked at their discs and saw calcification abnormalities that are correlated with having chondrodystrophy. Dogs that didn’t have chondrodystrophy didn’t have any calcified discs. We also looked at a sampling of puppies that showed that Tollers with chondrodystrophy had the same abnormal histopathologic changes that Hansen saw in the chondrodystrophic dog breeds. And then there’s the millions of MRIs that have been done around the world where the discs look abnormal in these chondrodystrophic dogs. So that’s probably close to, you know, 100%. I mean, I haven’t checked them all, but very high. How many of them herniate is a whole nother question. And I think we need to say ‘herniate such that the dog receives medical attention’, that the owner notices or something wrong and it goes into the clinic. Because we actually, in that same Toller study, 4 of the 14 chondrodystrophic dogs had herniated and they didn’t have clinical signs. And those were dogs of varying ages, so we didn’t have like, a great control for, you know, having them all a uniform age. There was a paper published out of Japan where they looked at medical problems associated with a colony of beagles that were kept there for research purposes. And these were beagles that, they had a nice life, they had enrichment activities, they got to play and be semi-normal dogs. And in that paper, about 10% of the dogs had evidence of disc herniation or, you know, severe enough back pain that they received medical care for it. And I mention beagles because beagles are homozygous for chondrodystrophy, or virtually homozygous for chondrodystrophy. So it would seem that at least in that breed, it was about 10%, which show these clinical herniation events that the owners would notice. I think in dachshunds, the numbers that have been reported are higher than that. And they are variable from breed to breed. But it’s a little bit difficult to really do a study, because, you know, the beagle study they followed them throughout their lives and said “Sometime in their lives, this happened.” And that’s where the 10% number came from. But if you’re not doing that, it’s a lot harder. And there’s thousands of papers showing that dachshunds are over represented and French bulldogs are over represented as dogs that have intervertebral disc herniation events. So that’s kind of a known thing. But some of the other breeds may be less common. When we started this project in Tollers, we were mapping short legs, not disc herniations. But when I went back and looked in the old listservs, there were a lot of Tollers that had been reported to have acute severe disc herniations. I think I found, like, 22, in kind of a search that I did, including some big winning dogs. And they were treated, interestingly, kind of differently in that they were like, “Oh, Toller’s acutely paralyzed”, and they often got euthanized. And it kind of seemed to come out of nowhere in that the people weren’t really expecting this, and the veterinarians probably weren’t expecting it, like this doesn’t really look like a chondrodystrophic dog, we’re not really sure what’s going on here. But in retrospect, yes, there are definitely herniation events in the breed, which go along with chondrodystrophy. And that’s true of the other sort of unusual or less common breeds that ended up having chondrodystrophy like Chesapeake Bay retrievers and Portuguese water dogs and, you know, other breeds that

we wouldn’t normally think of as short legged.

JH: Portuguese water dogs? Yeah. I would not think of them as short legged. I had an urge, by the way to ask you to define ‘listserv’. I’m not, I’m just joking. 

[laughter]

JH: For those who are too young to remember mailing lists. It was like Facebook before we had Facebook. That’s what she was talking about. 

DB: With no pictures.

JH: No pictures, no pictures. Yeah, no, I’m just joking, but I just had a moment of “Is anyone gonna know what she means by that?”.

DB: It was a way to discuss things in a community. 

JH: Yes. And we talked about dogs. 

DB: Yeah, where we talked about dogs. Portuguese water dogs are really interesting, because when we mapped the short-legged thing in Tollers to chromosome 12, we looked to see if other short-legged things had been mapped there previously, and Gordon Lark’s group had mapped short legs in Portuguese water dogs to the same region. And they hadn’t identified the mutation but they’re like, “Oh, there’s this, like, short-legged thing here that explains some of the leg variation in Portuguese water dogs.” And this was based on some really amazing, precise measurements that they took of a large group of Portuguese water dogs to study dog bone morphology. Anyway. So we kind of suspected that Porties would have that mutation. 

24:48

JH: Yeah, and I’m actually wondering whether we should explain mapping a little bit because this is my area of interest as well. It feels so natural to me to talk about it that I’m like, who wouldn’t understand that what Danika just said was that one group found a large region of the genome of DNA, where they were like, “Somewhere in here, there’s something going on that’s associated with this trait.”, and then the second group came and sort of got closer down and said, “This is the exact spot, and we can tell that this is what’s actually causing the trait.”. Do you want to add anything to that?

DB: Sure. Well, if we’re starting with Tollers, I’ll tell you that it’s usually a big chunk of the genome. Because they don’t have quite as much genetic diversity. I was able to look at some array genotypes and figured out that someone had mixed up the breeds on the arrays, because I said, “These aren’t Tollers, there’s too many chromosomes here.”, which is creepy. So in Tollers you can map to a big region. The Portuguese water dog study had also mapped to a big region. And they were kind of overlapping, so we thought maybe they were the same gene. The way we narrowed down chondrodystrophy is, we had looked at every gene within this large interval in Tollers, and there were a lot of genes there, and hadn’t found it, and then got the idea that maybe we should see if there’s any other breeds that have this kind of shared DNA with Tollers. Because there’s a lot of short legs in lots of breeds, was kind of the idea. And when my graduate student pulled out the breeds that shared the same stretch of DNA, it was the chondrodystrophic breeds. It was a hallelujah moment for me. There have been a few times in my career when I’ve run screaming down the hallway and that was one of them. I feel like, you know, obviously people are really interested in this, the reason why they’re interested in it is that this is widespread. At my hospital, UC Davis, the neurosurgeons here do surgery on one of these a day, every single day of the year, at just this hospital. And these are dogs that all come in, in horrible pain. So I mean, in my book, this is the most painful disease in veterinary medicine, and whether it affects your dog or not, if your dog has the mutation or you’re passing on the mutation, you’re potentially passing on that risk of having the most painful disease in dogs. And, you know, I just… I mean, it’s also painful to get hit by a car, but I would put it up there with being hit by a car. So this is incredibly common. Whether it affects, you know, one breeder’s kennels or one breeder’s dogs, it may or may not, but across the world it affects millions of dogs.

28:06

JH: So that makes it something that we definitely should be trying as a community to figure out how to deal with. And it’s wonderful that there is a genetic test. And I think what a lot of the questions I get around this, what everybody wants me to ask you, are things along the lines of… maybe I’ll sort of throw some of these out here and we can figure out how to go from here? Things like, what happens if the dog just has the one allele, is that, you know, what does the phenotype look like then? How much of a risk is the dog of A) being painful? Or B) herniating?

DB: Maybe we should just go there? 

JH: Why don’t we just go there. And also, I think at this point we can sort of agree that although a lot of people really focus on herniation, I think you’ve made it very clear that herniation is not the place to focus, and the sort of sudden paralysis. That’s the event that people… it’s very easy to see, and it’s really terrifying, and it’s really obvious what’s going on. But that is something that you don’t get without having passed through presumably this earlier stage of having been painful. And we should be concerned about the earlier stage. So I would argue that rather than looking at ‘Is the dog going to herniate?’, the question is more, ‘Do we have the chance of the dog herniating? And do we have this phenotype where the dog is liable to be painful?’ That’s where to start. Rather than saying, “I’m not going to worry about it unless I actually see dogs herniating in the dogs that I’m breeding.”, if that makes sense to you?

DB: Yeah, it does. I mean, we definitely have to talk about allele frequencies and breeds, but let’s just talk about one copy versus two, because this is where I think… my experience with the Toller breeders is, if it had been recessive, they could have handled it better and been happier about it. So the problem with this mutation is that it’s dominant. And while there is a difference in

calcification risk, which is sort of the end stage of intervertebral disc degeneration, there isn’t a difference as far as herniation risk between dogs with one copy and dogs with two copies. And that really bothers people. Because most of the things we talk about are recessive. And everyone’s really comfortable with like, “Oh, it’s a carrier, and we can still breed. And you know, we don’t have to think about what to do about that.” So we’ll talk about counseling in a minute. But the reason why it’s dominant is that this is a gain-of-function mutation. So there is no normal gene. The normal chromosome in dogs, in wolves, doesn’t have this gene inserted on it. So it’s different than when we talk about a mutation that causes a change in a gene. This mutation is that there’s an insertion of an entire gene on a chromosome where it doesn’t belong. And unfortunately, it’s inserted somewhere that pushes its expression in the intervertebral disc where it is not normally expressed. So there’s 20 times as much expression of fgf4 in the intervertebral discs of chondrodystrophic dogs compared to non-chondrodystrophic dogs. Basically, it’s ‘off’ in non-chondrodystrophic dogs, and it’s highly expressed. So it doesn’t really matter if it’s one or two copies because it went from zero to, you know, 100. So it doesn’t really matter if you go from zero to 100, or zero to 200, right? It’s still like, all of a sudden there’s a gene, a really important developmental gene, that’s being expressed in the wrong tissue. Does that make sense? So that’s why it’s dominant. Then we have to talk about allele frequency. So I said beagles are homozygous for this. So basically all beagles have it. So that isn’t something that you can fix within the breed, right? You can’t breed it out unless you do an outcross. There are other breeds where the allele frequency… I’m sorry, my computer’s telling me something is unstable. But anyway, there’s other breeds where the allele frequency is lower, and the bad version where this gene is inserted segregates. And so you can select against it if you want to. And in that case, you don’t want to do it all at once, because if the allele frequency is high enough, you’re gonna select against a huge number of dogs, right? So there can be other consequences of that. Like, there can be other variants that cause disease in the breed, or just that it affects, you know, a lot of people’s dogs all at the same time, and they don’t necessarily have a chance to sort of adjust their breeding program. But the fact that it’s dominant really challenges, because then you’re still producing affected animals or potentially affected animals. And you have to be able to talk to people about that. I guess that’s how I approach it as a breeder is that you want to be honest with people and tell them. And I still bred a dog with chondrodystrophy. After I found out about this mutation, I bred her to a dog without chondrodystrophy, and she only had one copy. So that meant that half of the puppies had a copy of chondrodystrophy and half did not. And I explained to the new owners that I was working on getting rid of this, I didn’t want to have it anymore in my breeding program. And obviously they were coming to me because they admired the dogs that I was breeding, and they admired the mother who had chondrodystrophy, and it worked out fine. Like, they were aware, they knew that they were taking a risk, most of them were already Toller lovers, so they were already, you know, interested in the breed. And it’s not like there were a lot of Tollers available that didn’t have chondrodystrophy, but still, I didn’t really have anyone who specifically asked to have it or not have it. I did make one placement where I wanted to make sure that the dog without chondrodystrophy went to that home. And that was a home where the dog’s owned by Mammoth Ski Patrol, and he’s an avalanche dog. He just got certified. I didn’t want that dog to have chondrodystrophy. I didn’t want a working dog who is potentially going to save – my son’s a skier – save someone’s life, you know, be in danger of herniation and having to retire early or something. But for most pets, you know, I suggest they get insurance and make sure that they could handle it if the dog herniated. It’s an expensive vet bill. At our hospital, it’s about $12,000 for a herniation event, to do surgery. But I think a lot of insurance covers it? I don’t actually have pet insurance, so I don’t know. 

JH: I imagine it depends on the breed.

DB: Yeah, I don’t know. I mean, I think the way they fix it is that they charge more for the breeds that are likely to herniate. And not…yeah. We don’t need to talk about pet insurance.

35:43

JH: No, yeah. Which actually – so many directions to go, so I want to make sure not to get us too far off track – but if you were a breeder who bred a dog with, you know, so say that there’s a breeder who is trying to get away from this in their lines, but you breed a dog, you know that the dog has the mutation. Aside from warning about herniation, with the knowledge that there may be some back pain even aside from herniation, would there be other recommendations you’d give to an owner? Things like keeping the dog lower weight, you know, in shape, watching for pain and considering pain meds?

DB: So there’s, you know, luckily, there’s a lot of work that’s been done on this in dachshunds because they have a higher rate of herniation than other breeds. And I think keeping dogs sort of athletic and lean and exercised, and trying to think about not doing exercise that might be likely to cause a herniation event. So, you know, Frisbee and landing hard, and things that are more likely to cause it is something that I think it kind of depends on the breed. In Tollers, for example, we sort of think, well, they’d be miserable if they didn’t get to retrieve and swim and go after ducks. But maybe they don’t need to be, you know, flyball dogs or something, I don’t know. But in dachshunds, one of the things that was interesting that was associated with a lower likelihood of herniation is stairs. So you’d think, oh, stairs are bad, but actually it seemed that maybe dogs that were climbing stairs were in better shape, and so they were less likely to herniate. But yeah. And then you said, give pain meds?

JH: Well, I said consider. Yeah, you’d have to go to your vet, right? 

DB: It would be depending on their veterinarian, and you know. But certainly being aware. And we found this mutation while I had a young dog who had chondrodystrophy – Pint, my dog, has one copy of the mutation – and I was competing with him in hunt tests. And, you know, watching him and paying attention, and he definitely had a bout of back pain that I might not have been paying attention to if I hadn’t been aware of this. But he decided that he didn’t want to go out and get a bird. Actually it wasn’t just me, but everyone who knew him was like, “There’s something wrong.” He would never say no to a bird. So he had some back pain then and he got anti-inflammatories and a long rest. 

JH: Yeah, I have seen this as well, the dog that usually wants to work that doesn’t want to work. And the temptation is to say the dog’s just being a jerk. But how… it’s so rare that that’s the actual answer. There’s almost always something going on. 

DB: Almost always. 

38:27

JH: Almost always. And when we talk about… we should definitely talk about allele frequencies in different breeds. But let me just ask this more general question first, which is that when you see a breed where you notice tests sometimes come back positive, saying that there is this allele in the breed, but it’s not a breed that’s much associated with diagnoses of IVDD or IVH [Transcriber Note – intervertebral herniation), is that going to be due to allele frequency? Or are there other genetics or something else about the dog’s morphology that can be protective? In other words, is just having that risk factor genetically worse? Is it a bigger risk in certain breeds than in other breeds? Or is it always sort of pretty much the same amount of risk? You know, one versus two copies, irrespective of what breed you’re talking about. 

DB: Yeah, I mean, it certainly would seem that there is a slightly different risk between different breeds. So in one of the papers that we published, we tried to look at the relative risk and it varied from 5 to 15, which is astronomically high, by the way. But nonetheless, there was some variability there, but the confidence interval is also really big. It’s a little bit of a difficult question to answer because you’d sort of have to be able to count all of the dogs of that breed that had the mutation, follow them throughout their lives, and then find out how many of them present with acute herniation events that cause neurologic dysfunction, right? If that was your phenotype criteria. So, you know, certainly dachshunds and French bulldogs seem to be the most likely breeds to herniate. But poodles also have a lower allele frequency of chondrodystrophy and we’ve definitely seen doodles that have herniated. So I mean, you know, it’s hard without being able to do some sort of really large longitudinal study to see who all out there is herniating. And by the way, I mean, it happens in mixed breed dogs, too, because a lot of these breeds are kind of popular and we definitely see mixed breed dogs that herniate as well. You asked me something a while ago, and I think maybe I didn’t get to the answer. And that is that yes, that there’s an environmental effect. And are there other, sort of, genetic causes to disc herniation. So what this mutation does is it prematurely degenerates the discs, so they’re at like an older state in a much younger dog. And then they live with those degenerated discs for a longer period of time, and therefore, they’re more likely to have a herniation event. But as dogs age, their discs degenerate just like ours do. And so, older dogs can also have intervertebral disc disease or herniation. It tends to not be herniation, it tends to be sort of a chronic single disc that bothers the dog, so it’s a little bit of a different kind of disease. But it’s not the only thing that can cause disc disease in dogs.

JH: Yeah, that’s very useful to make clear to people, I think, especially because in terms of the predictability of genetic tests, this one is actually pretty predictive. But I think there are people out there who might perceive it as not predictive because this dog tested as clear but then when he was 12 he did have this disease, so what’s going on? And the answer is, there can be other causes other than this genetic cause, but they tend to happen when the dog is older and we would tend to tolerate that more as the dog doesn’t have to live with it for as long, and we sort of expect things to go wrong as the body starts to age. 

DB: Yeah. And people, for example, who have back problems don’t have chondrodystrophy. So this type of mutation doesn’t exist in people. And yet, lots of people have back problems, right? So I mean, yeah, there are other ways to have, and other forms of disc disease, certainly.

43:17

JH: All right. So, and I think it’s… I actually was just answering a question on social media recently, where someone was asking about, are most of the diseases that we can test for they’re mostly recessive? And the answer is that yeah, mostly when a disease is dominant we can easily identify it and breed it out. And I think we’ve covered some of the reasons why this one can be hard to identify and breed out, because sometimes we just don’t notice that it’s a problem. But there’s also a reason that it has gone to high allele frequencies in some breeds. And that’s because it’s associated with a phenotype that we like. And one of the things that I found interesting, I was listening to a talk that you gave, you gave it somewhere. I don’t know where, from my perspective you gave it on YouTube. 

[laughter]

JH: But you talked about how short legs, there’s a different mutation which can also get us short legs, but doesn’t have this unwanted side effect. So I don’t know if it’s worth sort of talking about how… it’s just interesting to me that we’ve had this problem, it’s spread throughout a lot of breeds because we hadn’t realized there was a very serious problem so closely correlated with a phenotype that we’re so interested in. But there is another solution.

DB: Yeah, so let’s talk about what chondrodystrophy seems to do. So it makes the legs a little bit shorter. Not very much, maybe, you know, 10% shorter. It makes the skull a little bit wider. And I believe it makes the ear tips round. There’s maybe some disagreement on that with another researcher, but at least in my experience, it seems to do that. And so those things you could imagine may be selected for in certain breeds based on their breed standards. Okay, so there is a phenotype, it’s a subtle phenotype, but it’s the phenotype nonetheless. And then chondrodysplasia, which is the other term that we introduced earlier, is a more severe form of dwarfism. So the legs are much shorter, but it is not associated with intervertebral disc disease at all. So if one desires a dog with short legs, you can produce a dog with short legs and they don’t have disc disease if you just select for the chondrodysplasia mutation. The really interesting thing is that they do have a combined effect on leg length. So the breeds that just have chondrodystrophy without chondrodysplasia – I’ll just give a couple examples so people can kind of have a picture in their mind – cocker spaniels, beagles, and French bulldogs just have chondrodystrophy. Scottish terriers, Westies and Glen of Imaal just have chondrodysplasia. And the breeds that have both are dachshunds, bassets and corgis. And the Dandie Dinmont terrier has both and actually an additional extra copy of fgf4, which I think might be the shortest legged breed. We don’t know so much about that extra copy of fgf4. But if the thing that one likes is short-legged dogs, you can have short-legged dogs without having chondrodystrophy. 

JH: French bulldogs only have chondrodystrophy? I feel like…

DB: Well they have other things. 

JH: There must be other stuff causing the legs to be sure because I feel like Frenchies have pretty short legs.

DB: Sure, there are probably lots of things, I can name a couple of them. They have the dishevelled 2 variant that has contributed to their brachycephaly and their vertebral bodies, sort of their shortened spine and screw tail. And they have a number of developmental variants that affect their structure. And they are probably more likely to herniate because of the combination of variants. Whereas maybe the American cocker spaniels and beagles don’t have other things associated with structural changes to their body that might make them more predisposed. Oh, I keep, you know… I’m sitting here looking at this picture and I keep forgetting. Hansen actually originally looked at Pekingese. And I feel like I forgot to say the Pekingese. But anyway, Pekingese actually have both chondrodystrophy and chondrodysplasia as well. 

JH: Sometimes when the breed is so small it’s hard to even perceive that they have short legs because they’re so itty to begin with. 

DB: Yeah and you kind of have to lift up the coat.

[laughter]

JH: So let me pull that together and you tell me if I’m summarizing this right. It sounds like there are a variety of variants that are interacting to cause short legs. And some of them have side effects that we don’t like. And some of them don’t seem to have side effects that we don’t like. If you put a variety of variants together in a single dog, you’re liable to have shorter legs. And there may or may not be ways to get the super short legs without having to use some variant that has side effects, but we don’t really know that for sure. So it could be something that someone could explore if they were so inclined.

48:58

DB: Right. Yes, absolutely. Absolutely correct. And I think that this maybe doesn’t fit with your group as much as it would for others, but I will tell you that it seems that people from a dog showing perspective like the look of chondrodystrophy. So in breeds where it segregates, it seems to be popular, in that judges will pick a chondrodystrophic dog over a non-chondrodystrophic dog that’s next to it, and that’s an in multiple breeds. So that’s a challenge, if that selection, which is relatively subtle, but you know how specific breed standards are. You know, if you’re showing dogs then maybe it’s a problem to get rid of chondrodystrophy if your dogs then won’t be as good looking. 

JH: For sure, and that is exactly what I was thinking of when I was trying to think if there were other alternatives to it. I mean, I’ve noticed. I think a lot of people know that I have a soft spot for golden retrievers, and I’ve noticed that the show goldens do tend to have much shorter legs than the field goldens. I suppose you see that in a lot of the breed splits, that the working lines are just a lot leggier. 

DB: Yeah, I think that’s true. For all the ones that I can think of, that’s true. I’m trying to think if it ever goes the other way around, but I don’t… not that I’m aware of. 

50:29

JH: It probably does in some in some breed, someone will let us know. So, of course, it is not as easy as simply saying, “Well, I’m going to just remove the CDDY and swap in this,” was it CDPA, right? Swap in the other one. Until we have CRISPR working in dogs more easily. That was a joke! Because obviously, it’s not going to be that easy even then. But it’s not as straightforward as saying, “I’m gonna just breed this one out and breed this other one back in.” because we breed entire genomes, not individual genes. But I still would be interested in what your recommendations are for breeders. And I think we’ve established that even if you’re breeding in a breed or a cross that is not known to herniate frequently, it still would be advisable, if possible, to not have CDDY – the test is referred to as CDDY, so a lot of people refer to it that way. We haven’t been using that term. But it would be advisable to have a dog, to have all your dogs be clear if at all possible. But you mentioned how that was hard for you. I mean, you knew the consequences. But you still can’t just immediately drop all those dogs from your breeding program, because there’s certainly side effects to that, too. So maybe this is a good time to talk about different allele frequencies in different breeds. So there’s some breeds where it’s fixed, but there’s some breeds where it’s not. Are there some breeds where you think people could start just breeding it out more quickly because it’s not at such a high frequency?

DB: Oh, yeah, definitely. I mean, there’s breeds where it’s low and, you know, it would be something that if you were testing you could know about and get rid of relatively easily.

Yeah. I mean, it’s actually, sadly, in Danish-Swedish Farmdogs, I can’t seem to get away from it.

And not necessarily a really high allele frequency. And so if people test and make those breeding decisions, you can choose to not have it and, you know, it can be eliminated quickly. I think when it’s at that kind of medium allele frequency, there’s a strategy that we refer to as sort of breed and replace, right? So I told you I bred my chondrodystrophic dog. If I were going to continue in that breed, I could select a non-chondrodystrophic puppy to go on with. And that, if I had heterozygotes, would allow me in one generation to get rid of it. If you have a homozygote it’s going to take multiple generations, because you’ve got to breed to make the heterozygote and then breed again, to get the sort of normal, unaffected dog. So, I mean, that’s all possible. And I think that’s, you know, an individual breeder decision and maybe a sort of group decision amongst people that are talking about health, to move in that direction. I’m not sure… it’s interesting to think about whether, like, if you… I mean, since… this is gonna be hard, right? Since this is the FDC, is it okay to say I desperately need dogs with short legs and therefore I want to bring in another variant that causes short legs? I don’t know. That’s for you to answer, not me. 

54:27

JH: I don’t actually know. So I struggle with it sometimes, because on the one hand I like to say that we should be breeding dogs that are healthy. On the other hand, I do want to support the fact that the heart wants what the heart wants. And you perhaps teased me earlier about really liking hairy dogs, and I do. So a short time ago I had three dogs, two long-haired and one short-haired. I now have only two long-haired dogs. I didn’t think I was gonna want the short-haired dog but when I got him I was like, his welfare is actually better than the long-haired dogs. Not that having mats from time to time is a massive welfare issue, right? But, you know, I’m constantly, with the long-haired ones, I’m constantly like, “Oh, come over here, I gotta brush you.” or “I gotta pick that mat out.” or you know, “Go lie down while I get the clippers.” I lost my clippers a couple of months ago, it’s a whole thing. You know, and the short-haired dog, none of that. So is that an FDC level problem? Should I be campaigning against long-haired dogs? Should I be? Am I the hypocrite here, right? But at what level does it start becoming important? And I think I would say that if you can breed a dog that has short legs, and the dog’s welfare is not affected, I’m fine with that. If the dog can be a dog, and it’s not painful, and it can run and play, and you like the look of it, I’m okay with that. Yeah.

55:51

DB: We haven’t really talked about chondrodysplasia and what other things might be happening.

JH: Yeah, go ahead. 

DB: Well, it seems that chondrodysplastic dogs are more likely to be valgus [Transcriber note: limb joint bows inward towards the center of the body]. And then potentially, that may be associated with more issues with their elbows. And it’s, of course, not all dogs. But, you know, there’s that propensity there. I mean, it’s a variant that, you know, grossly affects the normal bone morphology and growth. So I mean, I’m not sure that it’s completely innocuous. I’ll just put it that way. And I did tease you about hairy dogs, but I’ll tell you. On my property we have this, I don’t know if you have this on the East Coast, we have burr clover here. So it’s like clover that grows these little round burrs. And those little round burrs do absolutely nothing to my Danish-Swedish Farmdogs, nothing. But on the Tollers they get in their coats, and I’m constantly having to comb them out and everything. And I said to my husband, if we eventually end up with all Danish-Swedish Farmdogs we can stop spraying for burr clover because it won’t matter anymore. So it’d be better for the environment. Short-haired dogs; good for the environment. 

JH: That’s a good argument. That’s a good argument. But how do they handle… Well, so some people argue that the short-haired dogs handle the cold – this is not your problem, this is my problem – that short-haired dogs handle the cold just as well. And I just have only had the one short-haired dog in my life. But he got cold very easily, and he had to have a warm coat in the wintertime. 

DB: Yeah, you know, my Danish-Swedish Farmdogs, my first one is from Sweden and she loves the snow. She’s quite hardy with her short coat. But she does have a winter coat. Yeah. But then you get to provide them coats. I mean, there’s positives.

JH: Yeah. So I try not to… 

DB: The collars and crates, right? It’s an obsession.

JH: Right.

DB:  I mean, only little dog people really have it, I think? The coats, along with the collars and the crates. But yeah. I have enough crates for all of my dogs to choose from three or four each day if they would like to. 

JH: That is nice. When I had the three dogs, two of them competed for the crate. And in fact, so one of them, the old one likes to be in the crate at all times – we’re totally off topic now – and the one who was the behavior case, I would be constantly sending him into the crate. And so the one who was always in the crate learned that when I yelled “Fitz get in the crate!”, she needed to come out of the crate. And I joked it was like flyball, because they would be passing each other, like in the crate, right? Like in the mouth of the crate, they’d be passing each other at high speeds as they swapped.

DB: I feel like you needed more crates. 

JH: Yes, that was what I was getting to. I definitely needed more crates, and I definitely had the very human response of “Where am I going to put the damn thing?” And I bought one that was really small, then the dogs wouldn’t use it because it was too small, and then I had to sell it on Facebook. Anyways. So, short-legged dogs. 

[laughter]

59:10

JH: Yeah, so let me just see if there’s anything. Yeah, I guess I was going to ask if CDPA is a risk at all, and you basically are saying that it probably is?

DB: I mean, I think that is… I have no data on how frequently it happens, but obviously there’s a lot of dogs with CDPA that don’t have any joint issues at all. And you know, it’s more just, from the FDC standpoint, you know, do you want something that has any sort of severe effect on bone morphology? I mean, I guess you could argue that small dogs are abnormal, and large dogs are abnormal, and pretty soon the only thing that’s okay is sort of a 30 to 40 pound village dog.

JH: Yeah, it is a question that I wrestle with. Is there a range of morphologies that are really ethically acceptable from a dog welfare standpoint? And is that range significantly different from what a village dog looks like? And I think as humans, we really like there to be lines in the sand. And so we would really like to be able to do a genetic test and say it has this and so I’m not going to breed it. But I don’t think there can be real lines in the sand for this one, I think we all have to find our own place.

DB: And I mean, there’s a lot going on in dogs that we don’t understand, right? But, you know, longevity, and little dogs live longer. So even though we would say, well, there’s this kind of 40 pound proto-dog that is maybe truly wild-type and hearty, it’s maybe not living as long as a little dog. And so, you know, how does… then it gets really confounding. Like, what is fitness in dogs? And, you know… 

JH: Is it as happy, right? You know. Yeah, so.

DB: And I think, I guess it’s just important to mention that because we’re saying, “Hey, you know, you can still make short-legged dogs if you select for chondrodysplasia, and they won’t have this increased risk of disc herniation, which is a catastrophic event, and they won’t have, you know, this potentially increased length of back pain throughout their lives maybe, or intermittent back pain.” But I just wanted to make sure that, you know, yes, those will all go down but I’m not sure that they’re completely okay and without risk.

JH: Yeah I think that…

DB: Because I feel like someone’s going to come back and say, “Look, my chondrodysplasia, dog has elbow dysplasia. And you said that was okay.” I didn’t.

JH: No, I think that’s… and I did want to make sure to ask you the question: is CDPA without risk? And the answer is no, pretty clearly. But we don’t know what the risk is, right? 

DB: Right.

1:02:08

JH: It’s not as clear as the CDDY tests, which we’ve discussed, very clear that that’s not even risk, that’s just a consequence. CDPA, a little less clear. So what the answers are for people who want dogs with short legs, I’m not sure. Certainly for people who don’t care as much, you know, maybe they just have some CDDY, they want to start breeding it out. If they were curious about what the allele frequencies in their breed were so that they could start thinking about, is this something where I have to sort of sit down with the breed club and try to figure it out at a high level? Or is there maybe not as much of it, and I can be pretty confident that I can just start removing it from my lines? Are there resources that have the frequencies in different breeds? 

DB: So the Veterinary Genetics Lab at UC Davis has some links online to some of their allele frequencies combined with some of the ones that we figured out originally when we did the first publication. And I think that the Wisdom Panel folks may have put out a publication where you could look up allele frequencies in breeds, at least for all of their other tests. Maybe chondrodystrophy isn’t on there. I’m sorry, I should probably have known that. But I don’t remember. But the VGL [Transcriber Note: the UC Davis site] one, I think covers, you know, at least the more common breeds. 

JH: I can dig that up and put that in the show notes for people. For sure. 

DB: Okay. And I can send you the one that may have it that I was just thinking of that came out from the other group.

1:04:03

JH: Yeah, if that’s easier for you to do, that would be great. If you don’t get to it, I think people can manage. Alright, so I had three questions from Patreon members, and I think we may have answered them. So Carolyn asks, “Is CDDY always harmful? Do we really know how much it increases the risk of IVDD in mixes?” And I think what you’re saying is, we’re pretty confident it’s always harmful. There are probably some other genetic and obviously environmental effects whether the dog will actually herniate. But having even one allele for CDDY is probably something you want to avoid.

DB: Yeah, and I guess the other thing to add is, at least when we did our hospital based study, we actually found that the relative risk for herniation was higher in mixed-breed dogs. And that kind of makes sense if you think about it. So if beagles have been going along homozygous for this thing and they’re herniating when they’re two years old, that’s going to be a problem, right? They’re not going to be potentially used for breeding. So it may be that breeds that are homozygous have selected over time for later herniation events or other things that might somehow decrease the risk so that they can go on. But if you take that away by looking at a mixed-breed dog, maybe that herniation risk is higher. At least the relative risk that we found was higher. So I think that we don’t entirely know what other things might be coming into play. And there’s… a lot of people have tried to map other things, and it seems to always come back to chondrodystrophy. So I don’t know that there’s other really strong genetic factors that are contributing to herniation risk. Because chondrodystrophy is just so overwhelmingly strong that that’s what you see when you do any sort of experiments to try and map. 

JH: Yeah, swamping your results. Fair enough. All right. And then we have Anna, who’s asking how strong a predictor of IVDD is CDDY, which I think we have pretty much answered. But she does ask “Why do we seem to see it, see IVDD, in much higher rates in some breeds? CDDY seems to be surprisingly common in a lot of breeds, like spaniels, toys, pinchers, Farmdogs, where I don’t hear about a high prevalence of IVDD.” So a pretty similar question to the previous question. And I think we’ve talked a little bit about how there may be other things in those breeds that make them less likely to actually herniate or actually show clinical signs, but it’s still not good to have that variant there. Would you agree with that answer?

DB: Yeah. And I just think that this person means ‘herniation’, not IVDD. 

JH: Yes. 

DB: So, and they mean ‘herniation associated with clinical signs of… neurologic signs’. Right? So I think that I just want to, you know, keep reminding people of that because yeah, I think they all have IVDD. And, you know, we could… you have to be… the only way to sort of histopathologically look at the discs is after death. So we were able to do that in a small number of Tollers that had died from other causes. But, you know, that’s a challenge. There’s some imaging that can be done that would show that the discs were maybe prematurely abnormal. And there were some studies that were done out of Finland looking at dachshunds and variation in calcification and abnormalities seen on some of these more specialized imaging studies, but they didn’t have dogs without chondrodystrophy, they actually just compared dogs with one copy to two copies. So anyway, I just keep wanting to clarify that. Yeah, there could be other things. There could be conformation, it could be that you just don’t know, because people aren’t talking about it. I mean, if we hadn’t had that old fashioned listserv I don’t know that the Toller people would have thought that there was really a big problem. I mean, it depends on who’s talking to whom. I have had Tollers for a while, 20ish years, and I had one dog that I owned herniate and two dogs with back pain. And dogs that I’ve bred that have herniated. 

JH: You said they’re all homozygous, correct?

DB: No, no, no.  

JH: Oh, it’s still segregating. 

DB: It’s still segregating, yeah. So in mine, one was homozygous and the two with back pain were heterozygous. The one that herniated was homozygous. Anyway. These were… the herniation event was associated with, you know, neurologic deficits. 

JH: Fair. 

DB: So, yeah, there’s variability. And, you know, I think you just have to ask yourself how you feel about whether that your dog might be in pain without them being able to tell you, or whether you’re producing a dog that’s in pain. Or what always was really hard for me is producing a dog that might have an acute herniation event where someone cannot afford the surgery. So we see this all the time, that people can’t afford the surgery and they euthanize the dog. And that to me is, even if it doesn’t happen very often, is something that I don’t want to be producing personally. 

1:10:11

JH: Yeah.  And also I noticed you mentioned that you said some imaging can be useful to assess what’s going on in the dog’s back, even if the dog is not having, sort of, obvious clinical neurologic signs. Can you go into that a little bit? What imaging is useful?

DB: Now we’re the blind leading the blind because I’m not a neurologist.

JH: Well, but another person asked if x-rays were useful and my initial feeling was no. But so, I’m imagining x-rays, then the next step up is CT, and the next step up is MRI. And I imagine MRI is useful, but not everyone really is thrilled about doing that just to check and see how their dog’s back is. 

DB: Yeah so, and maybe we should talk about this a little bit because in the UK, they’re promoting a scheme of counting calcified discs in dachshunds, and breeding dogs with lower numbers of calcified discs at two years old. And that disc calcification would be based on radiographs, or x-rays. X-rays are not great at detecting calcified discs, they’re hard to see on x-rays. If you move to sort of the next modality, CT scan, you can actually look at disc calcification. That’s like what we did in the Tollers. And it costs more money, it’s actually pretty labor intensive to even evaluate those CT scans for the disc calcification events…

JH: The dog has to be under general anesthesia. 

DB: Yeah, I mean, you can do a CT scan without general anesthesia, you can do it with a short acting agent. But still, that’s only available in a handful of places, and it would be expensive. And I’m not sure that anyone would really… it’s not available as a screening method. And if they have chondrodystrophy it doesn’t really matter how many calcified discs you see or not on the CT scan, they still have the predisposition to herniate at some point and that herniation event can cause neurologic problems. So I don’t find that those screening strategies have a lot of evidence for how efficacious they are. They’ve been doing them for a while in Europe, and they really haven’t made a lot of progress in reducing the herniation rate. So, you know, I don’t think that there’s any point in radiographing a dog or getting x-rays to find out whether they have a calcified disc or not. There’s a lot of studies in dachshunds that show that it’s not the calcified disc that herniates necessarily, but counting calcified discs was sort of a way for them to try and imagine that they were looking at the severity of the disease process. And I haven’t seen results that convinced me, that show what kind of effective genetic change you can make that way.

JH: Fair enough. So the…

DB: And MRIs, sorry, we didn’t get to MRI, but MRI is looking at something a little bit differently. So it’s looking at basically the hydration status of the inside of the intervertebral discs. And certainly chondrodystrophic dogs are known to have less, basically water, in the disc. It’s no longer a cushion, it’s sort of hard, and you can kind of see that if you look at a chondrodystrophic dog. But again, that wouldn’t be considered abnormal. Veterinarians and neurologists look at MRIs all the time of dogs that have chondrodystrophy, and so they would call those normal. Hopefully, you can still hear me there. My screen went blank. Anyway, so hopefully I answered?

JH: Yeah, I think what you’re saying is there aren’t any tests that are super useful to do, not imaging tests, that are super useful to do to assess the state of the dog’s back or the risk of whether it’s going to herniate. Which is, again, what a lot of the questions I’ve been getting are about risk of herniation and I appreciate your emphasis on not focusing on the risk of herniation to the exclusion of the back pain. And that if you’re concerned about whether your dog has pain, perhaps these imaging strategies aren’t the best way forward. The question I got specifically was about people who are looking for puppies, and what kinds of questions they should be asking breeders. And so if you, and again I feel like we may have already answered this, but if you are looking at a litter and you know that there’s a possibility that some of the puppies will have CDDY because the parents, you know, there’s some number of alleles in the parents, then is there anything else you should be asking about those puppies? And I think I would say, find out if the puppy actually has CDDY and then if you are really concerned about your dog having back pain, perhaps that’s not the right puppy for you.

DB: Yeah, yeah. I mean, I agree with that. I guess it would be nice to, you know, if you’re… I mean, I do agility with my dogs. So I don’t want a dog that’s going to have back pain. However, there’s a lot of dogs with chondrodystrophy that, you know, don’t have problems in their agility careers, but I just feel like, you know, we worry about all sorts of soundness issues and agility dogs all the time. And again, they can’t complain, they just sort of go, “Hey, I don’t really want to do the weaves.” or, “Hey, I’m gonna slide by this jump, because I didn’t like it.”, and then we wonder whether it’s a training issue or a pain issue. And sometimes I don’t want to run around the course either, especially if I’ve been course building. Anyway, so I can [indecipherable] is what I was gonna say. 

[laughter]

1:16:12

JH: And I think it’s also fair to say, in addition to dogs that work, I mean, I think you and I are both very aware of what it’s like when you have a dog who works or does sports and you’re asking them to do things, but there’s also the pet dog. Right? And sometimes we ask pet dogs to do things like go on hikes with us. But sometimes it’s just, the pet dog should be able to go up and down the stairs or get on and off the couch. And not to say that you weren’t thinking of this, but just to make clear to listeners that we are thinking about this, that even our dog is…

DB: No, I…

JH: Yeah, go ahead. 

DB: Yeah, no, absolutely. Absolutely. And actually, I have some friends who have a dog with chondrodystrophy, and they feel like he’s grumpy. And, you know, they’re convinced that it’s because his back hurts, and they feel like he’s less grumpy when he has pain meds. And I don’t necessarily know. Again, it’s apparent pain. You know, we can’t ask them, but it makes me wonder about behavior issues and how dogs are reacting. I know my single copy chondrodystrophy dog Pint – you can look him up, ‘Pint the dog’, if you Google him he actually is probably more popular than I am. 

JH: I was Googling you before this that I learned about Pint.

DB: You learned about Pint, yeah, he’s my little heart boy. So Pint has chondrodystrophy. And he retrieved the kickoff tee – since we just saw the Super Bowl – he retrieved the kickoff tee every time the UC Davis Aggies scored. And he worked for 44 games, so over a dozen seasons. And at one point the vet school bought him a really cool harness to wear that had a lot of things on the side that they wanted said. And it sat right on his sort of mid-thoracic area. And he showed me that it was painful to have that harness on, it was very clear. So I did give the harness back and go back to his cute little t-shirt. And this is a dog who’d never had an acute herniation event but had had back pain previously. And you know, I mean, he really made it clear that he didn’t want to go get the tee when that harness was on his back. And that was just like, you know, a little bit of weight across the spine. So.

JH: That is simultaneously a slightly sad but also adorable story. 

DB: He’s pretty cute. 

JH: Yeah. 

DB: He has a bobble head too. Not many dogs can say that. 

JH: Meaning that he likes to wiggle his head back and forth?

DB: No, they made a little bobblehead.

JH: Oh oh, they made an actual!

[laughter]

DB: It’s adorable. Yeah, super cute. They’re quite popular on eBay apparently or somewhere, some Toller person finally… they were like, “We wanted a bobblehead, and we finally found one!” 

JH: No, not many dogs…

DB: There’s a new tee retrieving dog now, and so I kind of forget that… You know, I mean, he’s been retired for a couple of years. But I ran into someone who was in the band when Pint was training and, you know, I’m like, “I’m the Associate Dean of Research at the School of Veterinary Medicine.”, and she’s like, “Wait, but you’re Pint’s mom!” Yes, yes I am. And she told me she was in the band. So I understood, cause the band really liked Pint.

JH: So dogs who have this mutation can have a full and wonderful life, but we should still be cautious of them and pay attention to things like stuff pressing on their back. And when they tell us that it’s uncomfortable, we should be thinking, why might that be?

DB: Yeah, and I mean, you asked me what I do and why I do it. I mean, I uncover things that affect dog health. And I guess, for me, this is definitely the most impactful thing that I have ever discovered. It affects a vast number of dogs. And as I was getting a lot of flack from people for making this discovery and telling them that their dogs might be unhealthy, it would get really hard and I would get sad. And I finally just started going into ward 5, which is our neuro ward. And every time I get down about how people are angry about this test, I go and walk in that ward. And I guarantee you, right now, there’s a handful of dogs that have just had surgery or about to go into surgery. And I call them zipper backs, because they have sutures all along their spines from really painful and aggressive surgery and a long rehab and a large vet bill. And this is the right thing to do. We should be getting rid of this.

JH: Well, thank you so much for coming here, and for saying all of that. I think it’s a powerful and important message, so I really appreciate you getting it out there.

DB: Thanks for having me. I appreciate being able to talk about it, cause I feel like there’s a lot of education that has to happen. And part of it is this fault of veterinarians, and part of it is just being really careful about how you describe something and making sure that everyone’s using all the same language.

JH: All right, let’s leave it there. 

JH: Hey, friends, some of you have asked how to support the podcast, so we’ve set up a Patreon page for it. For a small monthly pledge you help us pay for producing this podcast, and in exchange you get a chance to suggest questions for podcast guests and you get early access to podcast episodes. To find out more go to patreon.com/functionalbreeding. You could also help promote the podcast through subscribing to it through the podcast app of your choice and by leaving favorable reviews. If you’re interested in supporting the Functional Dog Collaborative more generally, or finding ways to get involved, go to the functionalbreeding.org website and click the support link. Thanks to everyone who has helped out we could not do this without you.

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JH: Thanks so much for listening. The Functional Breeding Podcast is a product of the Functional Dog Collaborative and was produced by Attila Martin. Come join us at the Functional Breeding Facebook group to talk about this episode, or about responsible breeding practices in general. To learn more about the FDC, check out the functionalbreeding.org website. Enjoy your dogs!

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