Episode 140: Multiple-Sired Litters

Dr. Greg Burns, DVM joins us to discuss multiple-sired litters, from what causes it to why breeders might want to use it to their advantage! Dr. Greg Burns is a board-certified theriogenologist (reproductive specialist) and is currently an assistant professor at Colorado State University.

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Transcript

Nate Ritter [0:29] Hi, everyone! This is Dr. Nate Ritter, the staff veterinarian here at Good Dog. Today I’m very excited to welcome back a special guest, Dr. Greg Burns. You may have heard him on our podcast previously, or seen him in one of our webinars. He was a member of our health symposium last year. Very excited to welcome him back. We went over his intro previously, but I’ll repeat it here for any new listeners. Dr. Burns is a board-certified theriogenologists, originally from Phoenix, Arizona. He received his DDM from Colorado State University in 1996 and entered small animal general practice in Phoenix. Upon returning to Colorado in 2000, he worked as an associate veterinarian at a South Mesa Veterinary Hospital in Fort Collins, where he eventually served as medical director for 18 years. While at South Mesa, he developed the small animal reproduction department, which included an international semen freezing and storage facility. Dr. Burns received diplomat status in the American College of Theriogenologists in 2009. He is currently the assistant professor of small animal reproduction at Colorado State University. So, welcome Dr. Burns. 

Greg Burns [1:30] Thanks for having me. 

NR [1:33] Of course. Today we’re going to be talking about a very interesting topic: multiple-sired litters. A good place to start, if you could, is explaining for our listeners what exactly multiple-sire litters are.

GB [1:42] When a female conceives from two different males in the same litter—at least two different males. It used to be called dual sire and now the most appropriate term is multiple-sire because sometimes there’s more than two males used. The offspring are born from different sires in the same litter. That’s basically the definition of the multiple-sire litter. 

NR [2:05] Can you explain a little bit more about the dog’s reproductive biology as to why a litter could have multiple sires? How is this even possible?

GB [2:11] The canine is a litter-bearing species. That’s the first thing. They routinely have more than one egg that can be fertilized. That’s normal for a litter-bearing species. That’s the first big thing, in my mind, that they have going for them for multiple sires. The other thing that I think about a lot with their cycle is receptivity. I think that’s pretty unique to canines—at least in our dometic population. They’re receptive for longer than many domestic species. For example, that proestrus period that they go through (which is 9 days), some of them are receptive in that period to start with. Then you go through the estrous stage (which is 9 days also), and they’re typically receptive that whole time. They’re receptive to breeding that whole time. That’s a long time to be receptive compared to, say, a cow (receptive for a very short period of time). I think that receptivity has something to do with it also. The other thing they have is their fertility period (that period where the egg can actually be fertilized by the sperm) is 72 hours in the canines. That period is a little bit longer as well, when you compare that to other domestic species. Really, their biology is set up to have multiple sires if it desires. They have a lot of things going for them in that way.

NR [3:40] They certainly do. Like you said, if it should be desired. Why would a breeder choose to breed their dam with multiple males?

GB [3:47] This isn’t new. It’s been approved by the AKC since 2000, so we’ve been thinking about this for over 20 years. They even went back a couple more years to say you could register litters starting from about 1998 from dual sires, at least with AKC. When I think of it, I think of it in two populations. I think of the working dog population. They want to increase their genetic gain as quickly as possible. Their genetic gain would be their genetic improvement, right? That would be for either detector dogs or seeing-eye dogs—things like that. However they define their genetic improvement, they want to increase that as quickly as possible. And then I think about the other population of breeders, like conformation dogs, and performance dogs. I think they think of it maybe a little bit differently. Maybe genetic diversity. So they would be able to see the offspring from two different males in one litter. I think that becomes really important in our canine population because, really, when you’re talking about the female, her prime reproductive years are 2-4 years old. Her genetics are really just as important as the males in many instances, but she’s limited. We can’t freeze embryos in the canines now. We can freeze sperm and keep it for 50 years, but we need to help her genetics along as much as we can. I think a lot of them think of that piece as well. In conjunction with the sperm samples that might be weakened, the older boys or the post-thaw motilities that we get with frozen samples, say less than 50%, they don’t want to waste that female’s cycle. Those are just a few reasons why I think this might be becoming more popular.

NR [5:32] Sure. You spoke to the semen being utilized in these cases. Would you say AI is more effective in these instances, or do you think natural breeding is preferred when trying for a multiple-sire litter? 

GB [5:45] That’s a really good question. They really do need help when we’re using these attenuated examples. If we’re using frozen thawed samples, or if we’re using chilled samples, or perhaps an older boy who may not have as good of a sample, I think artificial insemination would definitely be desired. I have heard of those instances where the boys are similar age, similar semen quality, and they do natural breedings back-to-back with success. Those I’ve primarily heard of in working dog populations. I think AI for sure in most instances would be preferable.

NR [6:20] Great. I know you’ve spoken to some of these points in our previous questions, but what are some potential advantages and disadvantages to this breeding method?

GB [6:29] When you think about the female’s genetics and not wasting her cycles—because again after 4 years old, the whelping rate and the litter sizes decline significantly in most of our individuals. It’s a little bit breed and size specific, but they do decline. So we need to help her genetics along. By not wasting her cycles, that’s probably the biggest advantage. The other advantage that we talked about is that you get that older boy’s sperm sample the opportunity, maybe, to do something without wasting the cycle. There’s that piece also. Maybe you’re improving conformation performance, genetics, more efficiently—quicker—by dual sires. That would be an advantage. Maybe increase genetic diversity. That sort of thing. 

The disadvantages are mostly additional cost. There’s that. Whether it’s stud fees or ordering the semen. Your veterinary costs are more. Like we talked about, you’re talking about TCI or artificial insemination. DNA. That’s another one that’s increased cost because you have to DNA everybody. Those would be most of the disadvantages. I think you need to find a veterinarian who is comfortable with it and who has maybe done it before. That might be helpful to you.

NR [7:52] Absolutely. You spoke to the cost of DNA. For our breeders that may not know, how can they know who the individual puppy’s father is? Do you recommend doing DNA testing in all these instances? 

GB [8:05] For sure. The rules have changed just recently, at the end of last year, at least with AKC-registered litters. AKC changed the way that they do their DNA analysis. They switched to these things called SNPs. It’s not unique to them. They’re using their own DNA registry and their own process. Anybody who is interested in registering the litter with AKC would have to go through the AKC for parentage, so there’s that piece. Some of them are already done. So if it’s a common boy that’s been used before, say 7 times in his lifetime, their DNA has to be on file anyway. Or if they’re used 3 times or more in a year, their DNA is required to be on file with the AKC. But the deal is all of the participants—however many males and the female and all the offspring—have to be DNA. It’s pretty easy. Cheek swabs are typically what’s done. It’s sent in. There is a fee with AKC to interpret it, but it’s not a big fee. They’ll interpret it and tell you parentage based on that.

NR [9:09] Sure. You spoke, during the AI question, relating to breed and size having an impact in terms of multiple-sire litters. Have you seen more success with particular breeds or particular sizes of dogs? Is there any kind of correlation there? 

GB [9:22] Yeah, that’s interesting. The paper that I was involved in two years ago did show an increase in litter size and whelping rate. I’m using “whelping rate,” but it’s not really conception is whelping rate—the way we think of that. But you can think of it as conception. So they whelped more often, and they had a bigger litter size when dual sires were used. I thought that was interesting. That came out of that paper for sure. 

NR [9:49] Definitely. Have you seen this method have more success in particular breeds? I’m sure this is, like you said, relatively new, within the past couple of decades, so the research might not be there, but any particular breeds that you might not recommend it in? Or others that you’d say you’ve seen more success for?

GB [10:05] I have not seen that, but I will say, just in general, speaking of certain breeds—or fertility in general—there’s that piece, and there’s the piece of using attenuated or weakened samples. We definitely see breed differences. That brings up a good point, too. You have to have the right expectations when you’re doing this. When you’re breeding in general, I think you have to have the right expectations, but I don’t think we know enough yet about real breed differences. 

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Mikel Delgado [11:49] You have questions, Good Dog has answers. Thanks for submitting your questions to Good Dog’s Mailbag. Today we have our resident veterinarian, Dr. Nate Ritter, here to answer a question from a listener. The question is: Is there any flea, tick, or heartworm medication that’s safe to administer to pregnant or nursing dogs? Most package inserts specifically note that they have not been tested on pregnant or nursing dogs. Some even say you should consult with your vet. My vet said if they don’t know the answer, then neither does she. Help!

Nate Ritter [12:21] Fantastic question. There are medications that are safe. Just because a product hasn’t been tested on pregnant and nursing dogs, it doesn’t mean that it’s not safe, which is why it’ll say consult your veterinarian to determine whether or not it’s appropriate to administer. However, if it was my dog, I would prefer to administer one where that testing has been performed. So, ensure you work with your veterinarian regarding this, but there are different medications out there. Just for a couple of examples: Frontline Plus, Heartgard Plus, Revolution, and Tri Heart Plus. Those do exist. I want you all to read the product label, to look at safety specifically for pregnant and nursing dogs. That’s where you’ll be able to find that information as to whether they say it is safe, not safe, or has not been tested. And then work with your veterinarian to make the best decision for the dogs in your program. 

MD [13:08] Thank you so much for answering our Mailbag question today. 

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NR [13:14] Back to the paper that you were discussing, in 2020, the study had found, of 29 dual-sired litters, that only 30% resulted in a litter of mixed parentage. Why is that percentage so low?

GB [13:23] This is one of the first papers that actually looked at what the rate is and percentage is and things like that. But historically, if you go back and look at literature with anecdotal reports (so not official studies of people’s experiences), they report less than 1% dual-sire litters being born or pups being born when bred with more than one sire to each sire. So the 30%, compared to that, obviously is really high. The other thing, too, is that we found that higher whelping rate compared to the single-sired litters. I thought that was interesting, too. It’s almost 90% of those girls became pregnant, versus about 76% pregnant rate with the single-sired litters. So I thought that piece was interesting also. But that 30%, when you think about it, because the first sample that’s used is not as good a quality as the second sample that was used—I thought the 30% was reasonable. 

NR [14:29] Any possible explanation for that difference in the whelping rate that you just mentioned? I think that was definitely interesting between the two. 

GB [14:36] I don’t know about that, honestly. There’s all kinds of theories out there: what the environment is when there’s more than one sample introduced, but then you have to deal with the competition piece—the sperm competition piece. That’s a real thing. I don’t know. I’m not positive about that, but it was a pretty interesting finding. 

NR [14:54] Fair enough. You’ve touched on this: the puppies from the multiple-sired litters were more likely to have the second sire as the dad than the first sire. But when only one dog’s semen was successful, and there was a 50/50 chance of it being the first or second sire, can you translate these results for our listeners? What might be involved in planning for the dual-sired litter? 

GB [15:15] Yeah, and expectation, right? I think that’s important—to have the right expectations. When you follow the protocol that we used, break it down. I know you read that paper. It’s a pretty complicated results section in that paper, to try to keep everybody straight. So breaking it down: 30% chance of having the dual-sired offspring when using that protocol. About 27% of those were from the first sire and about 73-74% were from the second sire. You get more from the second sire than the first sire. That leaves about a 70% chance that you have a single-sired litter when you breed with multiple sires—at least with dual sires, like we did. Of those, 50/50 were from either sire. That’s the interesting point, right? How come 50% were from either sire? We’re using that weakened sample on that first sire. We have to qualify that a little bit. When I say “a lower quality sample,” we’re talking 55% post-thaw on average, versus 70% post-thaw on average. I think that’s important to point out because historically that’s been what we would consider average or a little above average post-thaw motility, where the 70% would be considered excellent post-thaw motility. While it’s worse, it’s really not bad for a sample. What we struggle with these days, when these dual sires and the requests for them, is that the first sire is always a bad one. Bad like 40% or 30% post-thaw. For example, an 8 or 10 year old male. Both of those are much different than using a 55%, considered average or a little bit above average, good samples. There’s that piece also. You just have to have that right as far as expectation. Why there was 50/50, we don’t know. There’s all kinds of theories about that. Much more research is going to be needed to decide why that happened that way. Pretty interesting, though. When you take the overall parentage ratio and include the offspring that were bred with dual sire that whelped from one of the single sires, the parentage ratio overall—the semen quality wasn’t affected when you take the overall numbers. The point of that is if you have that, you might as well go for it, because there’s a fair chance that you’re going to get offspring from that first sire that you really desire that might not be quite as good as that second one. At least that’s what we found.

NR [17:50] Very interesting. You spoke to using different semen samples of different quality. Relating to your procedure, you mentioned the lower quality sample being used first. Thought process behind that?

GB [18:03] Again, lots of theories on that. I think the easiest way to think of that is we’re giving that one a head start. We’re giving that weakened sample, that lower quality sample, a head start. That head start is typically at least 24 hours. In our paper, it was 24 hours. It gives that sample an opportunity to go meet those eggs that are ready to be fertilized first. It gives them a 24-hour heads-up. There’s much more to that, and lots of physiology that needs to be looked at, but really to give that weakened sample a 24-hour headstart is the way to go.

NR [18:42] Is there anything else that you can think of that our readers or listeners should know about planning a multiple-sired litter? Anything we didn’t cover in our questions?

GB [18:49] The one thing you said is planning, right? For the best possible outcome, have the appropriate age dam—2-4 years old—and having that expectation that, if you’re using the weakened sample (I think this is where that 1% came from anecdotally because honestly I think they were using these samples that were so poor quality, 30-40% low quality) I don’t think you’re going to get the numbers we found. So you have to have the right expectation. Having that expectation, doing the planning, being ready for that additional cost, whatever the registration/DNA/veterinary costs—having that planning in place is most important. And then having the right expectations for the most positive outcome.

NR [19:39] Absolutely. Relating to that, in terms of planning, breeders that may not be as familiar with this, it’s so important to have someone experienced in reproduction to be able to help them on this journey. From my time in general practice, if I had a client come in and start to ask about this, I would certainly refer. Any recommendations in terms of where people might be able to find those resources? If their local physician isn’t able to help them, relating to this topic?

GB [20:05] For sure. There is a society for theriogenology, and there’s a registry there with veterinarians who have a specific interest in reproduction. They’re not all board-certified theriogenologists, nor do they need to be, but they need to have a level of experience and expertise in order to get the most positive outcomes. I think that’s probably the best place to find somebody in your area or in your state. You can narrow it down by region or state or whatever. And then they’ll have their specific area of interest, as far as do they do TCI, or are they comfortable with frozen semen—that sort of thing. The Society for Theriogenology website is probably the best resource for that. 

NR [20:48] Fantastic. Thank you all so much for listening to today’s episode of the Good Dog Pod. We’re so happy we could have Dr. Burns join us again to teach us more about this topic. Thank you again for joining us. We’ll see you back here in June for our next episode, all about summer safety and disaster preparedness for your dogs.