Genetic Resistance to Worms in Goats

Episode 47
For the Love of Goats

Genetic Resistance to Worms in Goats

If you have goats for very long, you may realize that some never need deworming while others need it frequently. There is definitely a genetic component involved in a goat’s natural resistance or resilience to worms.

In this episode I’m talking to Andrew Weaver, Ph.D., Small Ruminants Extension Specialist at North Carolina State University about genetic resistance to worms in goats and sheep. Although there has been a lot more research done on genetic resistance in sheep, goat owners can learn from their playbook and use some of the same selection tools for improving the worm resistance of their herds.

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Deborah Niemann 0:18
Hello, everyone, and welcome to another episode. I am really excited today to be joined by Dr. Andrew Weaver from North Carolina State University, where he is an assistant professor and an extension small ruminants specialist. And today we are going to be talking about genetic resistance and genetic selection for parasite control and parasite resistance. Welcome to the show today, Dr. Weaver.

Andrew Weaver 0:45
Thank you. And thanks for having me.

Deborah Niemann 0:47
I’m really excited to talk about this, because if people have listened to the podcast before, they know that a long time ago, we had a serious problem with dewormer resistance. And, at that time, none of the dewormers worked, and Mother Nature culled my herd and basically left behind the ones that were the most genetically resistant to parasites. And now I have very few problems. In the past year, I’ve dewormed one goat—we have about 25 adults—and none of the kids. So, I really, really am excited about the idea of genetic resistance. So, I’m excited to hear more about the research you’ve done, and how people can apply this to their own herds. So, go ahead and just get started by telling us about your research.

Andrew Weaver 1:39
Yeah, so I just recently started at NC State. I’ve only been here just about a year, not quite even a year yet. And so, I’m getting the research program and extension program kind of off the ground here at NC State, and we’re starting some projects this summer. But, I can give you a little bit of a background on my past research and what I’ve done through graduate school. So, I grew up in Michigan originally. I went to Michigan State and got involved with the sheep program up there, and through some connections ended up at Virginia Tech with Dr. Scott Greiner for my master’s degree, and did some work with hair sheep, with Katahdins, looking at “terminal sire options,” as we call it—essentially breeds that we can utilize in a crossbreeding system to improve carcass quality and animal value while maintaining parasite resistance in our commercial hair-based ewe flock that’s predominant here in the southeast United States. Spent two years there, and then got to know Dr. Baldridge up at West Virginia University in Morgantown, and ended up going up there for my PhD, a focus more on this genetic resistance to internal parasites, and that resistance, the mechanism of resistance, and the genetics that kind of undermine—underroot—that resistance in Katahdin sheep. And so, I spent a few years up in Morgantown working specifically with Texel, and Katahdin sheep, looking at those immune mechanisms, and then graduated last spring in the heart of COVID, and moved down here to Raleigh and started at NC State. So, most of my work has been with understanding both between breed variability and parasite resistance, as well as within breed variability and parasite resistance.

Deborah Niemann 3:28
Okay. And, even though most of your research has been done in sheep, we can really apply what you’ve learned to goats, because I haven’t seen much research on genetic variability of parasites in goats. But, this is something that, you know, once people understand the concept behind this, and the genetic selection tools that you use and everything, this is something that we can definitely apply to our goats. I heard Faffa Malan, the person who invented the FAMACHA chart—there’s a video on YouTube of him talking about how most people who have sheep and goats, they’re acting like a nurse, whereas really we need to be acting like a lion. That, you know, when animals are in the wild, the ones that have heavy worm loads and are weak and anemic and slow are the ones that are going to get eaten by the lion. And instead of being the lion, as owners, we’re constantly being the nurse, and constantly propping up these animals that just don’t have the genetics to resist that. So, can you tell us a little bit about the genetic selection tools that you used to determine which breeds, or even individual animals, had the best resistance?

Andrew Weaver 4:49
Yes, so the common metric that’s utilized to understand parasite resistance is fecal egg count. And so, fecal egg count is simply a measure of the number parasite eggs in a given quantity of fecal matter that you collect from that animal. And so, there’s a lot of metrics, there’s a lot of, you know, tools we can use—like you mentioned, FAMACHA scoring—that we can measure and try to assess the level of parasitism in the animal, but really, fecal egg count is probably the best in terms of quantifying true resistance. You know, a lot of times you’ll hear about resistance versus resilience. And a resilient animal is an animal that, you know, can certainly be infected, but one that can maintain some level of performance despite that infection. But, at the end of the day, they still have parasites in their gut; they’re still shedding eggs all over your pasture that can then, you know, develop and infect other animals. And so, while a resilient animal is one that itself might be just fine, it could certainly be propagating that parasite infection to other animals. A truly resistant animal is an animal that is able to identify that parasite infection, prevent that parasite infection from even taking place, thus decreasing or greatly minimizing or eliminating the fecal output of those parasites. So, you don’t get a fecal egg count, you have no egg shedding on your pastures, and no propagation of those parasites within your flock and your farm. And so, really, those resistant animals are the ones that we want to focus on, and fecal egg count is the best tool that we have available to measure that right now.

Andrew Weaver 6:32
So, the fecal egg count, it’s a fairly simple technique that most people can learn how to do. There are several labs around the country that offer those services. A lot of veterinarians are able to do fecal egg counts as well. And, as a PhD and not a veterinarian, we can use fecal egg counts as a quantitative tool—to assess the number of parasite eggs that are there to use as a selection tool—but we cannot use it as a diagnostic tool. So, those of us that are doing fecal egg counts outside of a veterinary practice, we’re simply using it as a genetic tool, a trait that we’re selecting on. If you’re curious about, you know, using it as a diagnostic to identify what worms are there, is the parasite level indicative of needing deworming, that would be something you’d need a veterinarian to do. And so, certainly, you can work with your local veterinarian and have them done. If you’re using them as more of a selection tool, you can often have them done at a lower price to be used simply as a selection tool.

Deborah Niemann 7:37
That was one of the things I noticed, because when we were dealing with dewormer resistance, I learned how to do fecals. And I never actually changed my mind about what I was going to do with the goat based on that. You know, I would see that the body condition would be terrible, the eyelids would be anemic, and I would do a fecal, and it would have an enormous egg count. You know, and so it was like, “Okay, why am I doing these fecals?” Like. it always just confirmed the fact that this goat needed a dewormer, which I already knew based on their poopy butt and skinny bones and anemic status. But, what was really interesting was doing it on goats who didn’t have problems. And that was one of the times when I, like, really became a believer in all the research I was reading, was when I had a buck who was dying from parasites. Because this was, like, back in the day when most people were saying, “Oh, if one of your goats has worms, they all have them. So you should deworm all of them.” So this one buck just had tons and tons of worms, and could not even stand. He was not able to stand for a whole week before he died. And I ran fecals on all the other bucks in his pen, because I had—I call it the “voices of veterinarians past” who were, like, screaming in my head, “Give all the bucks a dewormer!” And I did fecals on them. And I could barely find any eggs at all. And they were all in there together. So, like, obviously, there was a huge difference between this one goat and the other bucks that were in that pen with him. So, can you explain, so what was the difference between them?

Andrew Weaver 9:18
So, there’s an old rule—it’s the 70/30 rule. Seventy percent of your worms are generally carried by 30% of the animals in your flock. And so, this kind of goes back to that whole idea of, you know, selective deworming practices rather than deworming the entire flock or herd, because really, it’s just a small portion of that flock that most of those worms are contained within. And so, the vast majority—you know, 70% of your flock—generally has very low parasite burden. It’s really just those 30 that are carrying the vast majority of the worms. And so, the key is to identify those 30, and, you know, those are the 30 animals that you either want to select against, don’t keep replacements out of, they’re the 30 that you might want to consider culling, or changing your management practices to address the susceptibility of those 30.

Andrew Weaver 10:06
And so, when we do fecal eggs counts, for example, the key is, you know, don’t just do a fecal egg count on, you know, maybe 1 or 2 animals, but do fecal egg counts on the entire flock and do those counts at the same time. Because what we’re looking at is the variability within a flock, within a herd, within that breed, to understand which animals are more susceptible, and which ones are more resistant, when given the same opportunity for infection. So, that’s what we call “contemporary grouping;” we’re providing animals with, essentially, the same environment. We’re giving them the same opportunity to be infected, we’re giving them the same opportunity to perform, and some of those animals will get very infected, and some won’t. And there’s genetic ties to that variability. And, if we can measure that variability, if we can assess and we can quantify that variability, now you have a tool that you can say, well, they had the same opportunity to be infected, and, for some reason, this group of goats over here was able to prevent or greatly minimize that infection compared to these other goats. So those goats with very low fecal egg counts are individuals that are worth keeping in the flock, are worth keeping progeny out of. They’re the ones that are going to, more likely, have those mechanisms that can prevent and minimize that infection, and are going to be more genetically resistant. So, the key is understanding that variability in the context of a contemporary group—a group that has had an equal opportunity for infection—because then you can select, you can find those animals that are more resistant, you can identify that 30% that has most of the worms, and you can cull against them, or you can deworm maybe just that group instead of the entire flock. And you can address just the parasitism in that smaller group, hopefully maintaining a little bit more dewormer efficacy, minimizing just blanket treatments.

Deborah Niemann 11:57
I know a vet who raises meat goats, and she is very strict about culling. She says if a goat needs a dewormer more than once in its life, it goes to the locker, because she wants to be able to maintain a herd that is just genetically resistant to worms. So, what exactly is the mechanism for genetic resistance? Why are some goats going to be more resistant than others?

Andrew Weaver 12:26
That’s a great question. And a lot of the work that Dr. Baldridge’s does lab has done has helped to elucidate some of this. And it really is rooted in their immune response. And so, whether an animal is resistant or susceptible, all that is controlled by “is their immune system able to recognize and respond to that parasite infection?” And so, the classic model is with sheep. We think about the St. Croix sheep; it’s a Caribbean breed, it’s a breed that was developed, originated, in a very hot, humid area where parasites are extremely prevalent, and really, those sheep don’t survive unless they are resistant. I mean, natural selection alone has identified those animals that are very resistant, and the vast majority of St. Croix sheep are very resistant to internal parasites. On the opposite end of the spectrum, we have sheep like the Suffolk sheep. Suffolk sheep have not been greatly selected for parasite resistance, and they’re a breed that tends to be much more susceptible to parasitism. And so, we can take those breeds—they’re two different breeds, they kind of fall on either end of the spectrum in terms of susceptibility and resistance—and we can give them worms. We can give them what we call “infective larvae.” And we can look at how their immune system responds to that parasite infection. And so, we’ll raise these sheep in a confined area, an area that doesn’t have any parasites. The parasite that we’re primarily interested in is called Haemonchus contortus, it’s the parasite, really, of greatest concern to small ruminant production across the world. It’s a blood-consuming parasite. And so, we culture Haemonchus worms, and we can take those infective larvae, and we drench—we give those infective larvae to the sheep. And those sheep, because they were raised in a barn where the parasite is not present, those sheep are naive. They’ve never been exposed to the parasite before. So, when we give them those worms for the very first time, it’s the first time their bodies have ever been exposed to that parasite infection. And, we can look at how they respond during that first—what we call a “primary infection.” And then we can monitor that infection. We use fecal egg counts, FAMACHA scores we call “pack cell volumes,” a measure of hematocrit level, red blood cell percentage. And so, we’re measuring anemia status in those animals to make sure that none of them get too infected, or if they do, we treat those animals and eliminate that infection. But we can do this in a very controlled setting. And we monitor that infection for about 4 or 5 weeks, then we deworm all those animals, clear the infection, let those animals rest for a couple of weeks, and then we give them a secondary infection called a “challenge infection.” So, we give them another round of these infective larvae. We look at how does their immune system respond to the second time they see it. Because the more time we’re exposed to an antigen, a pathogen, the better our immune systems are at responding to that that pathogen. And so it’s the same way with worms, that the more times they’re exposed, generally, the better off they are. And that’s why young animals, whether they be lambs or kids, generally get much higher levels of infection, have much bigger problems with worms, than our older animals, our more mature animals, because they’ve been exposed a lot. They’ve seen the parasite, and their immune system has developed adaptive immunity to that parasite infection, and they’re able to respond better.

Andrew Weaver 16:03
So, we use these controlled infections. And then we monitor the antibody response; we monitor the cellular immune response during those controlled infections. And what we’ve seen is, like in our St. Croix sheep, that cellular response actually occurs about 4 days earlier than what it does in the Suffolk sheep. So, the immune system is able to recognize that there’s worms there, there’s worms in my gut, and it’s able to activate that immune response, and send those cells to the site of the infection, and do something about it. It’s able to do that about 4 to 5 days earlier than what it is in the Suffolk. And that difference, that delayed response in the Suffolk, allows that parasite time to establish, set up camp, essentially, inside the gut of that animal, and continue on with its life. Where, in the St. Croix, that early immune response, it identifies the parasite is there, and it says, “You’re not setting up camp here; you’re not going to live here.” And it’s able to eliminate that infection.

Andrew Weaver 17:08
And it does that in a few different ways. We get what we call a Th2, a T helper cell type 2 response, which is typically associated with parasite infections, as well as allergic reactions. And the term that’s commonly used to describe a Th2 response is “the weep and sweep” response. And so, “weeping,” we get mucous release, we get increased, you know, fluid flow essentially, as well as what we call “sweeping”—we get gut contractions that essentially wash, that sweep, that push that parasite infection out of the animal and make it a very unfavorable environment in the gut for that parasite to establish and continue to develop. So, we get that Th2 response, that weep and sweep response; it’s going to essentially flush those worms out. We also get, now those immune cells create what we call NETs, or neutrophil extracellular traps. Essentially the cells, they release their DNA—we actually have images of this that are pretty cool. Of these cells releasing their DNA, binding up the infective larvae, and when the larvae can’t swim anymore, they simply get washed out of the gut with the rest of the gut contents. It’s important to understand that the parasite does not attach to the wall of the gut. The parasite has to swim to maintain position. So, anything that stops that parasite from swimming, from moving, is going to cause that parasite to get washed out of the gut. And so, these cells are actually able to release their DNA, bind up the larvae, prevent them from swimming. That, in combination with that Th2 weep and sweep response, causes those parasites to be washed out of the gut. And then, Dr. Shepherd did some work looking at ATP energy levels within those larvae, and was able to identify, in those parasite resistant breeds, their immune cells, when they are exposed to those larvae actually cause a reduction in energy within those larvae. We get a reduction in ATP, reduction in larval energies, that can suggest increased larval death. If you have less energy, then you don’t want to swim anymore, and you’re more likely to get flushed out as well.

Andrew Weaver 19:25
So, summarizing all of this, the cells are responding earlier—4 to 5 days earlier—when they get there, they’re binding up these larvae, they’re decreasing their energy, they might be causing some of them to die. And then, that Th2 response flushes all of those larvae out of the gut. We get no larval establishment, we get no adult worms, and get no fecal egg count, and we have a truly resistant animal.

Deborah Niemann 19:48

Andrew Weaver 19:49
So, I know that was a bit of a long-winded response, but hopefully that summarized it.

Deborah Niemann 19:53
Yeah, I love it! That is great. It is so fascinating to hear exactly how that whole immune response works in terms of something like worms, you know? It’s… I don’t know, it’s kind of easy for me to understand it when you’re talking about microscopic bacteria and viruses and stuff like that. But, this is the first time somebody has really explained to me how the immune system can react to something that is more of a physical threat, like a worm, rather than something that’s just microscopic, like bacteria. And also, too, you made a really good point that I just want to repeat, because it’s really important for people to understand that the barber pole worms don’t attach themselves to the gut. That is, like, one of the most common misconceptions, that people think that they just attach themselves to the gut and just suck the goat dry, which is not the way that it happens at all. They’re just… I think, Dr. Joan Burke, when she was on, she said, they just kind of scratch and then suck up the blood that is released. So like, they’re drinking it, like, tiny drop by drop, but when you have thousands of them, those drops really add up.

Andrew Weaver 21:09
Yes, so they… They have a little tooth called a “lancet,” and they just scratch away at the lining of the gut, of the abomasum, and, like Dr. Burke said, consume that blood that’s released. And, you know, an adult female will only consume about 0.05 mLs of blood per day, which doesn’t sound like very much. But, if you have 1,000 worms that are there, that’s a 50 mL tube of blood every single day. And, on maybe a kid that only weighs 30 pounds, a 50 mL tube of blood every single day—that’s a lot for that animal to keep up with in terms of, you know, regenerating those blood cells and not becoming extremely anemic. And that’s where the barber pole worm has its terrible reputation and those side effects that we classically know with the barber pole worms.

Deborah Niemann 21:58
Yeah. And the reason it’s so important for people to understand that they’re not attached is because there’s a horrible rumor online, that actually slows people down, like, people don’t want to give their goats a dewormer. And the myth varies. Some people say, “Oh, this only happens with oral,” or “Oh, this only happens with injectables.” But, the myth is that if you give a dewormer to a goat that has a really heavy parasite load that all of the worms release at once, and then the goat bleeds to death. Which, the worms are not attached. So that is just completely wrong. Sometimes, even though you give a goat a dewormer, they still die, because they were too far gone. So, I just always, like… I like to bust any myths that I can do when I’m doing these and have, you know, professionals on here talking about, like, the way it really works, you know, the actual mechanisms. So, can you tell us a little bit more about how people can select for genetic resistance in their own herds?

Andrew Weaver 23:00
Yes. So, it kind of goes back to the old saying, “If you don’t measure it, you can’t select for it.” And so, first and foremost, you have to start measuring. And this is true for any trait. I mean, if you want to improve growth, you need to start measuring weights. If you want to improve prolificacy, or, you know, kids survival, you need to start selecting those animals that have more kids and keep those kids alive. The exact same is true with parasite resistance. If parasite resistance is something you’re interested in, the first thing you have to do is just start measuring it, start paying attention to it. And, just by paying attention to it, you will start identifying those animals that require less treatment, that have better FAMACHA scores, that have lower fecal egg counts. And that is the easiest and simplest way to begin this process of selecting for those more resistant animals.

Andrew Weaver 23:50
And so, simple tools that you have available on your farm that you can do, you know, keeping track of deworming records. Utilize selective deworming. Those individuals that need treatment, make a note of that. Make a note of when they require that treatment, what you treated them with, was that treatment effective, and keep track of those records. And a lot of producers use this, just simple deworming records, and culling those animals that require more treatment. And it’s not necessarily going to happen overnight. But over the course of 5 years, 10 years, you’re going to end up with a flock or herd that doesn’t require as much dewormer treatment. And so, that can be a very simple tool to use. FAMACHA scoring… After you’ve completed the FAMACHA certification process—there’s an online resource now available for that. So you can go online, and you can take some modules, complete the educational component of that, you submit a video, and you can complete your FAMACHA certification. Once you’re certified, you can then purchase an official FAMACHA card and use that system to identify those animals that may need treatment. And so, that’s a great tool. Again, it’s a great on-farm tool; you can use it out in the field. It’s just a little card you can carry with you when you’re out working with those animals. You know, any producer can use it. It’s relatively inexpensive. It’s a great resource as well. And then, like I said, you know, fecal egg counts, they take a little bit more work to collect. They take, potentially, a little bit more financial investment to have those processed. But, that’s going to be the tool that really tells us what animals are more resistant versus susceptible, rather than maybe just resilient. And so, I encourage folks to utilize fecal egg counts, if at all possible. Those fecal eggs counts, you can do them yourself; you can send them to one of the labs. If you visit the American Consortium for Small Ruminant Parasite Control, we have a bunch of resources available related to these tools. And one of them is some of the labs across the country—one in Texas, Louisiana at LSU, and then West Virginia—they offer fecal egg counts for producers at, I believe, $5 per sample. And so, it’s relatively inexpensive, especially compared to maybe some local options.

Andrew Weaver 26:09
We also have, when you want to move to the next step in the selection process and maybe utilize a tool that’s a little bit more accurate, we have what’s called “estimated breeding values.” And, estimated breeding values are simply genetic predictors of an animal’s genetic merit for a given trait. And these estimated breeding values are generated by the National Sheep Improvement Program in collaboration with Sheep Genetics down in Australia. And, we take all of our raw data that we collect, we take those fecal egg counts, we take growth data weights, you know, number of lambs or kids born or weaned And we submit all of that raw data, that information that we collected on the farm, we submit that to Sheep Genetics down in Australia, and they run some very advanced statistical analysis and generate these estimated breeding values. And these estimated breeding values, they control for a lot of environmental factors, and so we have a much more accurate selection tool as a result. It also pulls in pedigree information. So, based on maybe the resistance of mom and dad, that helps us predict the resistance of the offspring. And so, we get a much more accurate selection tool with these estimated breeding values, and we can use what we call “the fecal egg count estimated breeding value” to identify animals that are more resistant or more susceptible.

Andrew Weaver 27:35
I mentioned, the National Sheep Improvement Program is the organization that runs this analysis and the generation of this genetic information. But this technology, these tools, are available to goat producers. Participation is much greater on the sheep side, but I certainly encourage goat producers to get involved. It’s open, it’s available. And certainly, if you’re interested in this, I would certainly be happy to answer any questions and work with anyone later on. But, we can take those fecal egg count breeding values, and they fall in a range that is expressed as a percent change. And so, we’re looking at, you know, change in fecal egg counts based on genetics. So really, on the low end, negative 100 would be as low as we can go, because 100% reduction in something is taking it completely away. And so, animals with a fecal egg count estimated breeding value of negative 100 would be what we call the most parasite resistant animals. On the other side of the spectrum, we have animals within the Katahdin population, for example, that are close to 1,000 on fecal egg count estimated breeding value. So that’s 1000% increase in fecal egg count based on that animal’s genetics. And so, we can utilize this genetic tool and make substantial genetic progress, I guess, much faster than using those raw measurements alone. And so, really, when we think about, you know, where we’re going in animal breeding, what’s the next step, where are we going in the future, these genetic tools are a great resource to identify and select for those more resistant animals.

Deborah Niemann 29:08
Yeah, as you’re talking about this, I’m thinking about some of the sheep breeds, like Florida Cracker and Gulf Coast Native, that have really high resistance to parasites, which makes sense, because they have been on this continent for, like, 400 or 500 years. And so, you know, everything was organic then. Like, if they didn’t have the ability to survive… Because those are sheep breeds that live in the very wet, humid Southast, which is, like, the most wonderful place in the world to live if you happen to be an intestinal parasite. And, you know, if we look at our goats, most of our goat breeds have not been around for that long—well, they’re nowhere near that long. But, I mean, like, Nigerian Dwarfs, which is what I have, have only been around, like, maybe… Like, not even 100 years. Boers really got big, you know, in the 90s, so. And, we took these poor animals out of a desert and brought them, you know, onto the plains of Georgia and all these other places in the Southeast. So, like Faffa Malan said, like, we need to be the lion, because as a vet professor said to me years ago when I was dealing with all this, you’re never going to get control of it with drugs, because the worms are always going to be one step ahead of you. So we can’t just say, “Oh, what’s the best drug to give them?” Because, just because it works today does not mean it’s going to work next month.

Andrew Weaver 30:35
Right. And you made a great point there. I mean, we have breeds that have come from areas of the world that we’ve brought to the U.S. that, where they came from, it was the desert. They were not exposed to the same level of parasite burden as what we see here, and what these Caribbean hair sheep have been exposed to. And so, you know, breeds like the Boer, in the sheep world, the Dorper—those are breeds that come out of very dry climates. And so, typically, those breeds are a little bit more susceptible, because over their years of development, they haven’t really been forced to become more resistant. And so, it’s important to understand that that variability within—we have some breeds that are, you know, more susceptible or more resistant. Some of that depends on where the breed originated, and what it was selected for. Goats are naturally browsers, rather than grazers, and so if given the opportunity, a goat is going to reach up in the air and eat something, essentially, above itself or at its head’s height. And, up high like that, they’re not exposed to parasites to that same degree that animals—sheep—that are going to eat off the ground. And so, goats, their natural behavior has not resulted in them being exposed the same level of parasite burden as what some of the sheep have. And so, because of that browsing behavior, you know, it’s great from the standpoint that, if they’re allowed browse to consume, they’re going to generally have lower infection levels, because that browse is going to have a lower parasite burden. But, when we do take those goats and we force them into a grazing environment, and we make them act like sheep, and make them graze and eat forage off the ground, those animals are now going to consume a lot of parasites that naturally they would not normally be exposed to based on their—their natural browsing behavior, I should say.

Deborah Niemann 32:27
Yeah. This has been so informative and helpful. One of the things, I think, if people are listening to this, they might also want to listen to the interview I did with Susan Schoenian where she talked about the periparturient egg rise. Because that just fits in perfectly with everything you were saying about the immune system, and how, well, this goat just gave birth, and so now its immune system is not concentrating on the parasites like it was the day before it gave birth. So, I think, just putting all the information from these two episodes together, I think, will really help people understand the whole relationship between things, like, you know, the immune system, and kidding, and resistance to the worms. Is there anything else you would like to add, before we wrap up, that you think people need to know about this?

Andrew Weaver 33:21
I think, I mean, I think the big take home points are, you know, if you want to begin selection for parasite resistance, first and foremost, you have to start measuring those traits associated with parasitism. And that can be deworming frequency, it can be FAMACHA scores, it can be fecal egg counts, depending on how involved you want to get. And then, once you start measuring those traits, identifying them, you know, start to understand that variability within your own flock and make selection decisions on that, explore the opportunities for some of these genetic tools that are out there. And they’re a much more accurate selection tool than the raw data alone. So, explore some of these genetic options, and identify those animals that have lower fecal egg counts, that require less deworming, that have better FAMACHA scores. And those are the animals that you should be, you know, keeping around in your flock, you should be keeping daughters out of, and generating replacements from, So, again, it’s just one tool in the toolbox. When we think about parasite management, it really needs to be an integrated program. And unfortunately, there’s no one golden ticket that will solve all of our problems, unfortunately. And so, it needs to be a combination of these genetic practices and making our animals more resistant in combination with selective deworming practices, and good pasture management, and things like that to make more of an integrated systems type approach to this management.

Andrew Weaver 34:43
And I will say, the American Consortium for Small Ruminant Parasite Control, they have a lot of resources available at their website,, and a lot of what we’ve talked about today, it’s all summarized there. We have a fact sheet on genetic selection for parasite resistance. So, I encourage you to check out those resources that are available, and look at, you know, what are some other options, as well, that we can incorporate along with these genetic tools to improve parasite management on your flock.

Deborah Niemann 35:13
This is great! This has been so helpful and informative for people. Thank you so much for joining us today.

Andrew Weaver 35:20
I really appreciate you having me, and my information is on the WormX website, as well. My email and contact information are there. So, if you have any questions or would like more information, don’t hesitate to reach out and send me a message. I’d be happy to help in any way I can.

Deborah Niemann 35:34
Thank you so much.

Deborah Niemann 35:37
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Genetic Resistance to Worms in Goats pin graphic

1 thought on “Genetic Resistance to Worms in Goats”

  1. This is what the focus of selective breeding should look like…it only makes sense that by human hand or nature, the week die to make room for improvement in adaptation to the challenges of an organisims enviorment. I was disscussing low input farming as a theory as a part of my philosophy of decivilization a decade ago…everyone said it wouldnt work because you couldnt compete with big ag. That of course is not at all the goal…rather the development of strains of livestock and crops that dont need artificial chemicals, heavy machinery, or the denuding of the earth to produce a modest, and nutrient rich harvest, with a resonable amount of labor.
    Upon purchacing my land, i determined it to stepe and rocky for cattle to thrive evaan if i cut the forest and planted grass…i had eaten goat frequently at a jamacian restaurant in richmond when i lived there….so i began to plan on having goats, as i think we need to produce more of our own food. A neighbor told me or his struggle and toil with goats made me question this idea. Upon educating myself on breeds of goat, and there diffrent strengths, his misstake was clear. As mentioned in this podcast, boers are not fit for wet climates…i dicovered spanish goats were capable of surviveing and reproducing without human interferance! I recently found a lady with a hands off flock in my biosubregion,south east appalachia, and have been talking with her about buying a few next summer. Sustainable low input food production IS possible! Thanks for the website, its full of gems.


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