Episode 183
For the Love of Goats
An abscess on a goat does not automatically mean caseous lymphadenitis (CL). In fact, a study looking at 10 years of diagnostic testing at the Washington Animal Disease Diagnostic Laboratory found that roughly two-thirds of samples submitted for targeted CL culture came back negative.
In other words, two-thirds of the goats that had an abscess did NOT have CL.
In this episode, Deborah Niemann talks with Dr. Craig McConnel of Washington State University about what the study found and what those results mean for goat and sheep owners.
They discuss the difference between culturing an abscess and using a blood test to look for antibodies, why a positive blood test does not always mean an animal has an active infection, and why screening tests should not automatically be used to make individual animal decisions.
They also talk about Johne’s disease, OPP/CAE, test sensitivity and specificity, prevalence, and why it is important to have a plan for what you will do with both positive and negative test results before you test.
Featured Guest
Dr. Craig McConnel is a professor at Washington State University, where he serves as Director of Veterinary Medicine Extension and Director of Continuing Veterinary Medical Education. He earned his DVM from Washington State University and later completed advanced training in ruminant medicine, veterinary clinical studies, and epidemiology. His research has focused on livestock health, disease epidemiology, herd management, animal well-being, and the economic impacts of disease in dairy and ruminant systems.
For more information
- Prevalence and demographic trends of Corynebacterium pseudotuberculosis (Caseous Lymphadenitis) in domestic goats and sheep: A ten-year retrospective study from the Washington Animal Disease Diagnostic Laboratory
- Episode 88 – Testing Goats for CAE, CL, and Johne’s
- Episode 87 – CL in Goats: Caseous Lymphadenitis
- Episode 91 – Johne’s Disease in Goats
- Abscesses and CL in Goats (article)
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Transcript
Intro 00:03
For the love of goats! We are talking about everything goat. Whether you’re a goat owner, a breeder, or just a fan of these wonderful creatures, we’ve got you covered. And now, here’s Deborah Niemann.
Deborah Niemann 00:18
Hello, everyone, and welcome to today’s show. I am really excited about today’s guest.
Deborah Niemann 00:24
I just realized it has been four years since we talked about caseous lymphadenitis here on the show, and last time it was with Dr. Claire Burbick, who was also from Washington State University, and that was in episode number 88, and she talked about biosecurity testing in general, and this is actually an extension of that talk.
Deborah Niemann 00:45
We’re gonna really get into the nitty-gritty here because Dr. McConnel was one of the researchers who looked at 10 years of CL test results at Washington State’s diagnostic lab, which is where I personally send all of my tests, so it felt cool reading the study and going, “Oh, I’m part of all those negatives that they got.”
Deborah Niemann 01:06
So, welcome to the show today, Dr. McConnel.
Dr. Craig McConnel 01:08
Yeah, thank you for having me. Appreciate it.
Deborah Niemann 01:09
So, in case somebody missed those last episodes, which was four years ago, and they’re not real clear on what CL is, could you tell us a little bit about it?
Dr. Craig McConnel 01:17
Yeah, I’ll do my best. Now, to be fair, I have become a non-clinical vet over the last few years, and am now really buried in research here at WSU and Vet Med Extension.
Dr. Craig McConnel 01:26
But basically, caseous lymphadenitis is an organism that causes abscesses, and those abscesses in small ruminants, or other animals, to be fair. But typically, we think of it in terms of small ruminants, can be either superficial or internal. And so, therefore, they have some production limitations, but they also can end up impacting things like meat quality or wool quality in sheep. And ultimately become problematic from the standpoint of spreading throughout a herd, throughout a flock, and possibly leading to, like I said, production losses, but also just general impacts on well-being.
Deborah Niemann 01:57
Yeah, because I think a lot of people who are slightly familiar with it, think that it’s just a cosmetic thing. I’ve actually heard people say that you know it just looks ugly because there’s an abscess, but they can actually wind up with abscesses internally, like on the lung, which is where it winds up affecting their general health.
Dr. Craig McConnel 02:12
Yeah, exactly. And obviously, the trick there is if it’s not superficial, where we can see it, and it is internal, they can go undiagnosed for quite some period of time, and they can ultimately have those impacts, either production limiting or just impacts on an animal’s well-being again, without us knowing it for you know an undefined period of time that becomes diagnostically challenging.
Deborah Niemann 02:32
And then this is one of those big three that I always encourage people to test for because you don’t want it in your herd because it is not curable and it is highly contagious. Can you talk a little bit about why it’s so hard to get rid of it once it is on your farm?
Dr. Craig McConnel 02:47
Yeah, actually, can I circle back real quick though to the big three because I do want to make mention that the reason we looked at this was driven by an interest in the larger landscape of biosecurity impacts of both lentiviruses and Johne’s or Mycobacterium avium paratuberculosis alongside CL and caseous lymphadenitis.
Dr. Craig McConnel 02:48
So we ultimately explored this data set through some funding that we got through USDA and through a mechanism called the National Animal Disease Preparedness and Response Program, which allowed us to establish some baselines by looking at these 10 years worth of data, so that we’ll have some baseline understanding of what’s out there in the event that we start seeing changes due to some, you know, unfortunate introduction of a foreign animal disease or otherwise that might look similar. So that was actually what drove this whole project in the first place.
Dr. Craig McConnel 03:32
In answer to the question you just asked, though, about managing CL within a farm and ultimately the issue within that biosecurity space, the organism itself is really resilient. It’s really tricky to remove from an environment. I actually just did a refresher, by looking at the Merck Veterinary Manual to kind of see what’s out there currently in terms of talking about both the treatment space and the cleaning up space.
Dr. Craig McConnel 03:55
And as you just said, the treatment space is effectively non-existent. There are some listed opportunities for attempting to treat, but you’re really not going to cure. But then within the landscape of an environment, within you know your herd scenarios, once you’ve got the contaminant, it’s just really tricky to remove it. And I actually pulled up some data we put out into one of our newsletters. I think it was three or four years ago, and I have to look at this other screen. That’s why I’m looking away.
Dr. Craig McConnel 04:18
Where we pulled up some data that we had done through our field disease investigation unit here at WSU within the vet school to look at some sampling that was done at a fairgrounds that had had some contamination. Animals had been allowed into the fairgrounds that had CL, and so we were able to take samples from a washing area, a barn walkway, a weight scale, a few pens and fences, and ear tag applicators, and then we did some culture and PCR work on that, and ultimately the PCR work is what we focused on.
Dr. Craig McConnel 04:44
And I was just looking at the data we’d put out there, and in that line of sampling, we had the presence of CL, Corynebacterium pseudotuberculosis, which is the organism that causes CL, on two ear tag applicators, one of which had been disinfected with chlorhexidine.
Dr. Craig McConnel 04:59
And we think that the reason it still had the CL was — I’m sort of conflating the disease with the bug — but the Corynebacterium, as an organism, was because there was a little organic matter still attached to it, which harbored the organism. Whether the organism was alive or not, I’m not sure because that was a PCR result.
Dr. Craig McConnel 05:15
But to come back to your question about the contamination and the management within the farm and the environment, it just persists and it can be around, and it’s quite tricky, and it can hide in little places like an ear tag applicator, which means that you then move it from the next animal or to the next animal, and if that is a live organism, then you’re potentially infecting the next one. So that’s the trick with this thing; it’s really resilient.
Deborah Niemann 05:35
Yeah, and I was just so amazed and impressed and excited when I saw your study because it does cover 10 years and 139,000 submissions covering 121,000 animals and 20,000 herds, which that’s the biggest sheep and goat study I’ve ever seen in terms of like the number of animals. So this is like really really valid. Just in case anybody wonders, like, well, how many animals were included here? It was huge. So, what findings surprised you the most?
Dr. Craig McConnel 06:07
Yeah. So, actually, and before I answer that question, this is a good opportunity for me to say that that data set is huge, and it was really unwieldy. And if you read through the paper and you have a chance to look at it, what you’ll see is that there’s a lot of missing pieces, which meant that we could get the tally of prevalence related to those 139,000 samples, but when you start breaking it down by sex or by breed or by other discriminators, we’re missing tons of data because things don’t get recorded when they go into the kind of data sets, which is the limitation.
Dr. Craig McConnel 06:34
But we still have thousands and thousands of you know samples and individuals to look at for each of those different discriminators. But this is an opportunity where I need to say that Hanna Sihler, who is a fourth-year veterinary student here, who took the lead on this paper and on this project, did a phenomenal job because this data set was so unwieldy, and she had, luckily, a background in data management at a high level with coding and some skill sets that I don’t have actually. She was able to pull this all out and do what she did, and therefore she’s the first author on the paper.
Dr. Craig McConnel 07:02
Okay, so I wanted to mention that because these kinds of studies are quite tricky, and that’s why they don’t get done. That’s why this data doesn’t exist out there. It’s just it’s hard work to get at it. As far as the surprising results, I think you and I had spoken previously about the fact that the culture results indicated that roughly two-thirds of culture results that were submitted for targeted culture of this organism came back as negative, which means that there are a whole lot of abscesses out there that actually aren’t related to Corynebacterium.
Dr. Craig McConnel 07:31
And while people who are in the field and maybe submitting these samples may know that, I think those of us in general sort of think that the assumption is: if you’ve got an abscess, it’s probably going to be CL, and that doesn’t seem to hold true.
Dr. Craig McConnel 07:45
And I was actually looking at some data that Claire Burbick, who you mentioned before for that episode 88, had brought to light a number of years ago when we put together a newsletter article. And she suggested that the data that they had in-house at the time suggested around 60% of culture results were coming back negative as well.
Dr. Craig McConnel 08:00
So these results stand up against sort of anecdotal work that they had done without this larger data set, and then really put it in the framework of roughly two-thirds of those samples that are being targeted for culture based off of what somebody thought would probably be CL are not necessarily CL.
Deborah Niemann 08:15
Yeah, and I just think that’s so important, especially for people who, like, spend a lot of time on social media, where if you mention an abscess on an animal, so many people will just instantly say, “Oh, that’s CL. It’s all doom and gloom and horrible.” And the reality is, which I said this over and over and over again, you can’t tell by looking.
Dr. Craig McConnel 08:34
Right.
Deborah Niemann 08:35
And some people are scared to get it tested because they’re like, “I don’t want to know because I don’t want to have to think about putting down this animal.” And the reality is, there’s a two-thirds chance that it’s going to come back negative. And if it comes back positive, then okay, you have a decision to make. But at least you know what you’re working with.
Deborah Niemann 08:51
And I definitely practice what I preach because when I have found abscesses on my animals, I get the vet out there, I do the culture, I send it in to your lab, and they’ve all come back negative, including the one who I really was mad at this goat because it was like it came back as just like normal skin bacteria, and it was like right there below her jaw, like right where the classic CL is. I mean, you know, I freaked out more on that one than any of them, and I’m like, how could you injure yourself there?
Dr. Craig McConnel 09:23
Right, right.
Deborah Niemann 09:24
Like, you know, why couldn’t you injure yourself and get an abscess somewhere else at least?
Dr. Craig McConnel 09:30
Yeah, I mean, it’s funny. Again, I think it’s just one of those things that we’re all worried about CL. Therefore, it must be the problem.
Deborah Niemann 09:36
Yeah.
Dr. Craig McConnel 09:36
But, you know, for those of us who’ve worked in the livestock space in general, small ruminant or large, abscesses are just part of the game. They’re everywhere. They’re around all the time, and ruminants in general are really good at walling off infections and making abscesses. That’s what they’re made to do. So it’s not uncommon to have abscesses, and they certainly don’t need to be CL.
Deborah Niemann 09:56
When you think about, especially, like, what goats eat with the browse and everything, they get in there with all kinds of brambles and prickly plants and stuff. And honestly, I feel like it’s surprising they don’t get a lot more abscesses if they’re out in the woods and consuming a lot of browse.
Dr. Craig McConnel 10:12
Yeah, exactly. I mean, they’re certainly open to those sorts of superficial infections all the time. So anyway, I think that was the most surprising finding for me in general. The other prevalence measures made more or less sense. We didn’t find a huge prevalence of immune responses and that, you know, I sort of expected that, but yeah, it was definitely the culture results that really brought to light the fact that we do want to be aware that if we don’t look, we don’t know.
Deborah Niemann 10:36
So there’s actually two different kinds of tests that you talk about in this study, one of them is the culture, which is what you would do if you have a goat with an abscess. You need to get the vet out there to get that culture sent into the lab. But the other one is this biosecurity test that Dr. Burbick talked about when she was on the show four years ago, and that’s the biosecurity test: one tube, 3 mL of blood, red-top tube. Send it to your lab, and it gets tested for CAE, CL, and Johne’s — all three.
Deborah Niemann 11:06
Again, we’ve had all negative tests on our CL and the others too, except for one CAE test way back, like over 20 years ago, that was a false positive. But everything else has been negative through all the years, and again, so the blood test is completely different. It’s a screening test for your whole herd because you can’t swab pus that’s not there. So how do you know if you have, you know, just purchased some goats that have internal abscesses or something that you can’t see? And that’s the purpose of the blood tests. So can you talk a little bit about the blood test and what it looks for?
Dr. Craig McConnel 11:44
Yeah, so the one that we use here is called an SHI, and it’s a synergistic hemolysis inhibition test, which is just looking at antibodies. So it’s looking at an immune response to an organism and telling us whether or not there’s an indicator that that individual animal has seen the pathogen and mounted a response to it. The liability with any immune response tests, though, is that if you’re testing a younger kid or younger lamb, you can have potential maternal antibodies. So they drink the colostrum, they absorb the antibodies — those are now in the system as well. You can have vaccination.
Dr. Craig McConnel 12:15
Now, I know CL is a little tricky on the vaccination side. I’m actually, to be honest, currently not totally sure if we even have a vaccine that anybody is getting access to. It seems like that’s become a bit of a challenge. But if an animal has been vaccinated against CL, then they’re going to have an immune response, and that vaccine is not considered a DIVA vaccine. And DIVA vaccines are vaccines that make an immune response that is differentiable from a natural immunity. And so, if an animal is vaccinated to CL, you cannot differentiate that from natural immunity, which means that an antibody response could be infection, but it could also be vaccination.
Dr. Craig McConnel 12:49
So that becomes the issue with any of the antibody-driven tests: is that there are options for demonstrating immunity — maternal immunity, vaccination, or infection. That means that when you get the result, you may or may not actually be dealing with an active infection. You may be dealing with previous exposure or otherwise. So that’s important because, as you just said — and I’m really glad you said it — the serologic screening tests should be used as screening tests.
Dr. Craig McConnel 13:12
And it’s common that people want to use them as individual diagnostics to make choices for the individual animal. But you really should be careful about that. I’m going to defer a little bit here away from CL and talk about Johne’s for just a second because we’re talking about the biosecurity screening, and they all become part and parcel.
Dr. Craig McConnel 13:29
We just published another paper off the same dataset. It’s in the American Journal of Veterinary Research (AJVR). Easy to find. It’s open access. You can search for Johne’s, WADDL, McConnell, and AJVR, and you’ll find a paper that’s equivalent to the CL paper. In the Johne’s space, historically, the serum has been, unfortunately, used in many cases to make individual animal decisions on farms. It’s meant to be used exactly as you said, Deborah, to create a landscape of whether or not my herd may be infected. So now I can start thinking about how I’m going to manage the individual animal through things like fecal culture, fecal PCR, to see if they’re actively shedding, to ultimately manage the infection pressure within my herd.
Dr. Craig McConnel 14:10
In the Johne’s landscape, there’s now two ELISAs available. One’s an IDEXX; that’s a historic one. It has poor sensitivity, which means that it doesn’t do a good job of actually identifying animals with infection. There’s a new one called VMRD, also an ELISA, that has apparent increased sensitivity, but is sort of an unknown application in the real world. So it’s been established to have a high sensitivity. It should identify infected animals at a higher level than the IDEXX.
Dr. Craig McConnel 14:36
When you compare the data across the landscape of, again, over 100,000 samples from WADDL for 10 years, what we found is that the VMRD was showing about a sixfold increase, on average, both individual sample or herd level, relative to the IDEXX.
Dr. Craig McConnel 14:36
And that becomes this huge issue in the small ruminant space about what lab do you use, which tests are they running, and oftentimes people are getting positive tests where previously they got negative because the lab that they’re now using might have switched over to a VMRD. That VMRD test is the only validated test for small ruminants. Therefore, some labs have decided to use it, including WADDL, for a period of time until they reverted back to IDEXX because of some unknowns about how to actually apply the results.
Dr. Craig McConnel 15:13
So the point is, whether we’re talking about CL or Johne’s, whenever we’re talking about antibody tests, the diagnostic capacity of the test is as important to understand as the application of that test to your herd, and in all cases, the application of the diagnostic test should be to identify the likelihood that the herd or flock is infected, not to make individual choices at the serologic level. You then want to do the culture, or then want to do the PCR, to start having a larger conversation about the individual animal and how do I manage that animal as they come into kidding or lambing maternity pen, or exit post-lambing, post-kidding, into, you know, the neonatal pen.
Dr. Craig McConnel 15:52
And are they shedding? Are they giving infection pressure? All that sort of thing. So I wanted to highlight that because, whether we’re talking about CL, or Johne’s, we’re now working on the lentivirus — so OPP/CAE (ovine progressive pneumonia/caprine arthritis encephalitis) — paper on the same dataset. It is really important to understand the utility of the test, and the reality is that different tests have different capacities for actually identifying infection or non-infection. And that’s, that can be a little tricky, but it’s important to know.
Deborah Niemann 16:18
Yeah. So when I had that goat over 20 years ago that came back positive for CAE on the screening test, we decided because she had daughters who had nursed from her who were negative, which is why it was like okay, this is probably a false positive. But to be sure, we did a PCR on her and on her daughters to make sure that we were not getting false negatives on her daughters. All of the PCRs came back negative, and that goat actually lived a very long, healthy life. She was the most long-lived goat on our farm. She lived to be 16 and a half, so she was obviously a very healthy goat.
Deborah Niemann 16:54
So, what would be the next step if somebody got a positive on a CL blood test?
Dr. Craig McConnel 17:01
First question is: What’s the age range? Is it possible that this is a maternal antibody? If so, then that animal might not actually be infected, but the dam might have been. So that’s part of that conversation.
Dr. Craig McConnel 17:01
Second question is: Is it possible that there’s vaccination in the background? In which case, there could be exposure — or sorry, there could be an antibody response because of the vaccine. It has nothing to do with infection.
Dr. Craig McConnel 17:20
Third question is: Is it possible that they had an infection and cleared it? And this is just an immune response that indicates an animal is not carrying.
Dr. Craig McConnel 17:28
And, to be honest, this is where I start going off the rails a bit in terms of my expertise because I don’t know what the odds are of an animal being exposed to CL through, like, that ear tag or ear notcher that I just mentioned, seeing the organism, mounting a response, but never actually maintaining an established infection.
Dr. Craig McConnel 17:46
I don’t really know how those overlay, but you certainly want to ask the questions: Is it possible that this animal just has an immune response but not an infection? But then you go from there to: If I think that this actually is real, it probably has an infection, it’s mounting an immune response.
Dr. Craig McConnel 18:01
Then it becomes a question of: Is there an opportunity for shedding and infecting my premises? Are there superficial abscesses that have the potential to leak the organism that I ultimately need to manage? Versus, this animal might be realistically infected, but it’s internal. In which case, I have the welfare perspective, I have the production aspect, but I don’t necessarily have to concern myself so much with the contamination space because I’m not seeing open abscesses. I mean, that’s CL.
Dr. Craig McConnel 18:29
Johne’s, you start asking the question about shedding through feces or in utero. And so you know you’re kind of working through those steps of this likely to be real? And if so, then what are the next steps to reduce infection pressure?
Dr. Craig McConnel 18:40
And or what’s my risk aversion? Do I just remove these animals regardless? Because I can, and that becomes part of that larger conversation. And it is an important conversation to have, obviously, for everybody. The risk aversion becomes a big question for all of these diseases.
Dr. Craig McConnel 18:56
We’ve had a lot of conversations around this, around Johne’s. If you’re managing a small flock, it’s basically your pet, you know, your pet space, and you’ve got Johne’s-positive animals or CL-positive animals, but there don’t seem to be any production limitations or manifestations that would be impacting welfare, then, at some level, it doesn’t matter.
Dr. Craig McConnel 19:12
If you’re showing those animals and you want to have negative because you don’t want to take the disease to other premises, or, you know, that becomes part of the entry space, you have to have negative, then that’s a different conversation.
Dr. Craig McConnel 19:23
So I think it is really important that we’re always thinking about what are you going to actually do with your test results before you even get the test result. And this comes up all the time. Why are you running the tests in the first place? You should never run tests if you don’t know what you’re going to do with the answer. And if all you want is a negative answer, but you’re not prepared to deal with a positive, then you probably need to rethink whether or not the test should even be run.
Deborah Niemann 19:45
I think it’s important for people to know that because a lot of times, people think that a positive just automatically means that the animal has to be put down, and that is definitely not the truth. Like, you don’t have to do that. There are so many other options for that.
Dr. Craig McConnel 20:02
That really came to light with the Johne’s when the VMRD test came online and we were seeing a lot more positives where there had always been negative. The question was: Are these false positives? Was the specificity maybe not as high as we thought it was? And specificity is just saying the likelihood of identifying a truly negative animal, which means that you can end up having false positive if the test isn’t particularly good.
Dr. Craig McConnel 20:20
So the trick with these diagnostic test characteristics is that their application in the real world is actually dependent on the prevalence. So the positive predictive value of a test, as an example, is driven by the prevalence. If you have a really low prevalence in a population, your positive predictive value is ultimately not good, for lack of a better way of putting it.
Dr. Craig McConnel 20:41
So, like in your case you described, we had the one positive. It sounds like your herd is negative. In other words, there is no prevalence. And so, if you had a specificity of 99%, that means one out of 100 can be expected to give you a false positive. And in your case, that was the one. You got the one.
Dr. Craig McConnel 20:57
If you have a prevalence of 50% you have a massive disease load. The positive predictive value actually becomes a much higher prediction. It actually is — it’s much more valuable, and you’re more likely to have true positives than false positives. So that becomes part of the conversation as well.
Dr. Craig McConnel 21:10
And so, back to your point, when you get the results, you don’t necessarily need to make the abrupt decision to cull or to euthanize or to do anything until you sort of have that, take a deep breath, think about what we’ve got, think about whether or not this is likely real. We’ve always had negatives, and now I have a positive. Is that likely real, or is that likely to be my one false positive that’s expected at some point? Are there additional diagnostic tests that can be done to validate this? Because there’s usually another test you can do to start making those comparisons and then make the decisions.
Dr. Craig McConnel 21:40
And unfortunately, sometimes people do what you just suggested, which is I get a positive, I make a rash decision, and it’s not really based on the reality of the situation.
Deborah Niemann 21:48
Yeah, I know somebody who had a positive Johne’s test, and she contacted me because she was like, “So I should put him down, right?” And I was like, “No, you should do more testing.”
Dr. Craig McConnel 21:49
No, definitely not.
Deborah Niemann 21:59
Yeah.
Dr. Craig McConnel 22:00
We have whole herds and flocks that were euthanized because of that.
Deborah Niemann 22:03
Yeah.
Dr. Craig McConnel 22:03
And, you know, you just say, “Oh no, no, no.” We, you know, again, that was so rash. Like, let’s take a step back and do some additional diagnostics.
Deborah Niemann 22:11
Yeah, and in that case, she did put the goat down, and the necropsy came back negative for Johne’s. She’s like, “I should have listened to you.” I was like, “What can I say?”
Dr. Craig McConnel 22:18
I mean, that makes you feel good, but it’s not the answer.
Deborah Niemann 22:20
Yeah, yeah. I’m like, “I’m sorry, I was right.” Like…
Dr. Craig McConnel 22:24
Honestly, the study, alongside I teach epidemiology here in the vet school. It’s been really good for me to sort of rethink the diagnostic testing space and the on-the-ground part of it because the results are one thing, but it’s the application of those results within the environment that you’re talking about that actually matters.
Dr. Craig McConnel 22:41
And I know that I’ve done clinical work for years, but you still kind of have to have a reset sometimes to think about how you’re going to take those results and use them. And ultimately, like I said, really every test should be run with an understanding that a positive or a negative has an outcome that I should already have planned for. You never want to be caught out with, “I’m going to run this test, but I don’t know what I’m going to do if I get a result.”
Deborah Niemann 23:00
So, what was the percentage of the blood tests that came back positive?
Dr. Craig McConnel 23:06
What we found on the SHI tests, overall, number of sample submissions and individuals. So, on the sample level for goats, 3.7%. At the individual animal level, because some individual animals provided more than one sample, over a hundred thousand individuals. Again, 3.9% prevalence.
Dr. Craig McConnel 23:22
At the sheep level, sample prevalence 9.9, individual 10.7. And then within the herds for goats, we found 9% and within the herds for sheep, 18%. So you know, really at the individual and sample level for goats, we’re talking around 4%, and sheep, we’re pretty much talking about 10%.
Deborah Niemann 23:40
Yeah. So again, for anybody who’s scared to test, the numbers are really very low in terms of how many test positive.
Dr. Craig McConnel 23:47
Yeah, exactly. And if you go through the paper, you see that we broke it down by how many samples were tested for a given herd. We didn’t have herd size, per se, but we did have the information to suggest that you submitted 10, somebody else submitted 20, somebody else submitted 30 over these years. And the more samples that were submitted from a herd, the more likely that they were to have a positive.
Dr. Craig McConnel 24:07
So we think that that was related, one, to herd size, but also probably due to herds being deemed infected that were doing ongoing testing and, you know, kind of following that through. So there’s kind of a combination pattern going there, which ultimately means that there’s a whole lot of herds that are negative, and then you’ve got a smaller number of herds that are positive. And so, when you start breaking it down by individual animals and individual samples, there’s an overrepresentation at the herd level for those positives. So yeah, to your point, people shouldn’t be afraid to test because, you know, it’s entirely likely that you have a negative herd.
Deborah Niemann 24:39
Yeah.
Dr. Craig McConnel 24:39
But again, if you’re going to test, be prepared for the positive, and then have a plan for, you know, if you get it.
Deborah Niemann 24:44
Yeah. Although I always tell people that it is really a good idea to buy from herds that have a history of negative tests.
Dr. Craig McConnel 24:53
Yeah, absolutely. I mean that’s the best case scenario, right? If you’re going to have an open herd, then really thinking about your source stock is this huge, and doing the best you can in that space.
Deborah Niemann 25:03
And the other thing, too, that sometimes people don’t think about that if you want to get sheep to bring onto your farm, and they’re going to have any kind of interaction with your goat, you’re going to do a leader-follower in the pasture with one of those species, that over 9% of the sheep were positive. If you bring in sheep that are positive, they could infect your pens or pastures or whatever, and then your goats could wind up positive.
Dr. Craig McConnel 25:28
Yeah, exactly. The trick with our sheep results was that we only had around 18,000 samples versus 120,000 goat samples, so it is a much smaller representation. I think that we have a more selective sampling range on the sheep side, more targeted sampling probably, in many cases, which is more likely to give you positive results because you’re, you know, you’re getting specific people who are interested. But you’re not wrong, if you’re bringing sheep into a goat scenario, or vice versa, you know, you just got to keep in mind that it’s entirely possible that that could be the infected animals. So pre-testing, quarantine, all of the above become part of the layout for bringing any animals into a herd or flock.
Deborah Niemann 26:05
Yeah, absolutely. And I think, from what I’ve seen, it does not seem that there are that many people who have sheep who test. The dairy goat world, it seems to do a lot of testing, but it does not seem to be so much with sheep. And if you’re not testing, then you’ve got all these animals running around out there infecting each other. So, to me, it’s not surprising that the sheep are testing higher when people do start testing.
Dr. Craig McConnel 26:30
Yeah, I mean, you’re, you know, you’re living in this space more than me, so I don’t doubt that you’ve got plenty of folks who just don’t do any testing, and that is what it is. And again, maybe it doesn’t really matter in certain scenarios if there’s really no evidence of illness, morbidity, or mortality. But it does matter if you’re exposing your animals to that source, and, you know, that’s where the game is played, obviously, at the biosecurity levels, knowing that going in.
Deborah Niemann 26:53
Were there any unanswered questions about CL that you had when you got done with this?
Dr. Craig McConnel 26:59
You know, one of the questions I would love to ask — and there was no way to ask it with this data set — would be the overlap of parasitism with these outcomes. In my clinical time, I worked in Australia for a number of years, been in Colorado for a while, and then now I’m up here in Washington, from Idaho originally. I think, particularly in the goat world, parasites, parasites, parasites are my top differentials, always. It’s just a tricky thing to manage. Everybody knows that.
Deborah Niemann 27:23
Yeah.
Dr. Craig McConnel 27:23
But what I don’t know is that overlap between that space of management and some of these disease states, and whether or not there might be some compromise that helps drive some of the outcomes that we see. I’d love to know that. I don’t really know how to even ask that question without, you know, a line of funding that is pretty substantial, but it would be quite interesting just to see if, in fact, some of this management is actually tied together across the landscape of multiple infectious agents. But that’s outside the premises of the study in general.
Dr. Craig McConnel 27:52
And honestly, I was pretty happy with what we found. I think the trickiest part, like I said when we started this conversation, is this: the data that is in hand in these kinds of data sets, has huge gaps because not every submission comes with all the information that you’d love to have. And so, you know, it’s a bit of a frustration because you’d love to be able to give answers at a more robust level across the full data set, so people would have those in hand. But that just doesn’t exist, and that is what it is. And so we do our best with the kind of data that we have in hand.
Deborah Niemann 28:18
Yeah. Is there anything else that you think people need to know about CLor the testing that we haven’t talked about?
Dr. Craig McConnel 28:23
I don’t think so. I mean, I think we’ve really hit the high points. I will say it’s a fairly easy read. It’s open access, so if people are interested in the paper, it’s in Small Ruminant Research — easy to get at. But no, I think we’ve really touched on the key points, which come down to, if you’re going to run diagnostic tests, understand that the serologic testing in general is meant to establish whether or not there may be infection pressure within a herd.
Dr. Craig McConnel 28:45
Then the question becomes one of the management space, not, “We’re going to remove all the animals, we’re going to kill or cull.” It’s just establishing whether it might be there, and then having a second look at the situation. And alongside that, I know I’ve said this multiple times, but I’ll say it again. Before any testing is taken forward, you really should have a plan for if you get the results you don’t want, because it’s nice to just have a strategy in hand so that you’re not surprised if you get those results.
Deborah Niemann 29:10
That’s one of the things that I’ve talked through with some people that I’ve worked with because it’s one of those things. Like, I always say the answer to most questions is, “It depends,” and this is one where it depends on so many things. Like, are these pets? Are they backyard milkers? Are you showing? Are you selling offspring? There’s so many things that would factor into what you do. How much land do you have? How much housing do you have? Like so many things, you know.
Deborah Niemann 29:38
And if it is a beloved animal, you know, maybe you do have a milking herd or a show herd or whatever, and this one beloved animal that you bought because you felt sorry for it at the sale barn, and now you regret it. You know, there’s probably a way that you can keep that animal on your farm without compromising everybody else if you really want to do that.
Dr. Craig McConnel 29:58
Yeah, exactly. I think that’s the key. It does depend. And honestly, that’s tricky because you get a result. It’s kind of — it is black and white. It’s a positive or a negative, and so you feel like your response should be black and white as well. And that’s just not the case in most scenarios.
Deborah Niemann 30:11
Well, thank you so much. I got so excited. Like I told you in the email, I got so excited when I saw that two-thirds of cultures come back negative because, if you hang out on Facebook much, you know it’s almost 100% of people saying, “Oh, you’ve got CL,” if you talk about an abscess. So I want people to know that is not the case, and that they should not be afraid to test. I have been very relieved every single time I have sent you guys pus in a tube.
Dr. Craig McConnel 30:39
Yeah, that’s good. I’m glad, and yeah, you’re like the case scenario for why you should do it, just to get some clarity and some peace of mind in many cases. Yeah.
Deborah Niemann 30:49
Yeah, exactly.
Dr. Craig McConnel 30:50
Yeah. Awesome.
Deborah Niemann 30:51
All right. Thank you so much for joining us today.
Dr. Craig McConnel 30:54
My pleasure. Absolutely. Thanks for inviting me.
Deborah Niemann 30:56
And that’s it for today’s show. If you haven’t already done so, be sure to hit the subscribe button so that you don’t miss any episodes. To see show notes, you can always visit fortheloveofgoats.com, and you can follow us on Facebook at facebook.com/lovegoats podcast. See you again next time. Bye for now.
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