Baa's and Bleat's - The AASRP Podcast
Baa's and Bleat's - The AASRP Podcast
Dairy Goat Drugs with Dr. Michelle Buckley
Join us for a discussion about subclinical mastitis in dairy goats caused by non-aureus Staph species (NAS) with Dr. Michelle Buckley. This research was completed during her time as a post-doctoral associate at Iowa State University with support from the USDA National Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Program, Mitigating Antimicrobial Resistance Across the Food Chain, Grant/Award Number: 2021-69015-33501. Dr. Buckley is currently an Assistant Professor of Clinical Practice at Texas Tech University: https://www.depts.ttu.edu/vetschool/about/meet-our-team/faculty/michelle-buckley/
In this episode we discuss two drugs that can be used in an extra-label manner to address subclinical mastitis in dairy goats during the dry period: Orbenin DC (cloxacillin benzathine) and ToMORROW (cephapirin benzathine). Dr. Buckley's work evaluated how long it took for both drugs to leave the goats' bodies after administration in both meat and milk as well as how effective they were at curing subclinical mastitis due to non-aureus Staph. She also evaluated antimicrobial resistance development due to treatment with these long-acting intramammary products.
The published work that we discuss is titled "Pharmacokinetics of long acting cephapirin and cloxacillin after intramammary administration in dairy goats" and it can be found in the Journal of Veterinary Pharmacology and Therapeutics here: https://onlinelibrary.wiley.com/doi/10.1111/jvp.13445
Additional publications will be added to the episode notes as they become available.
As part of this research, the Dairy Goat Extension and Education website was developed to provide veterinarians and producers with resources for ensuring antimicrobial stewardship and milk quality in dairy goats. This website includes short video training modules as well as electronic records templates and other useful resources: https://www.dairygoatextension.org/
As we mention several times during this episode, the drug use discussed here is extra-label and will require extended withdrawal recommendations to avoid violative residues in the food supply after use. Please contact the Food Animal Residue Avoidance Databank for guidance here: http://www.farad.org/
If your company or organization would like to sponsor an episode or if you have questions about today's show, email Office@AASRP.org
M I C 50.
Sarah:Hi, and welcome to our next episode of Boz and Bleats. Today we are talking to not only my good friend, but also the producer of Boz and Bleats, Dr. Michelle Buckley. So it's been rough for us to get started recording because we've been chatting so long here. But so she just finished her research, her residency at Iowa State. So she's going to tell us all about her super interesting research in the GOAT world. Welcome, Dr. Buckley. How are you doing?
Michelle:Hey, Sarah. Thanks so much for having me. I'm doing great. It's so good to have some time to catch up. I feel like we cross paths in meetings and never really get to actually talk very much. So it's good to see you.
Sarah:Okay. So give us a background. Tell us where you started, how you got here. You've been and worked at a million places and a million schools. So just give us the highlights.
Michelle:Oh my gosh. I don't know if that's a good thing or a bad thing. So yeah, I was born and raised outside Rochester, New York. So we do crop farming. I didn't grow up with livestock. I begged my family every Christmas for a pony and thankfully never got one. Um, but I had an ant with horses, so I got my fix that way. And I was thinking I would be an equine vet when I went to college. I went to a tiny little engineering school in Hoboken, New Jersey called Stevens Institute of Technology. And I played volleyball there and rode on the equestrian team. And riding fancy horses made me realize that I actually shouldn't be an equine vet. But I say I'm a reformed horse girl. And yeah, so did undergrad there, got my master's at Montclair State University because I didn't get into vet school the first year that I applied. So there you go. Then I got into vet school at Western University of Health Sciences in Southern California and never thought I would live in Southern California, but off I went, and I'm very thankful that I did. It was a really great experience for me, and their unique curriculum really helped me gain the skills I needed to, I think, be successful, or what I consider somewhat successful so far. I haven't quit yet. And then I was in practice for four years out there, did small animal GP and emergency, and I had my own ambulatory um food animal practice as well. And I taught during that time with my alma mater and realized I really loved teaching. And so when the opportunity presented itself to pursue a PhD in a pharmacology residency at Iowa State, I realized that was kind of the next step for me in my educational career. And so my passion is educating people about where their food comes from and how we keep it safe.
Sarah:That started this new role. Where are you now?
Michelle:Oh, yeah, that's right. I'm at Texas Tech now. I'm an assistant professor of clinical practice at Texas Tech.
Sarah:And that's the brand new vet school down in Texas, right? It is, yes, yes. All right. So it's coming along nicely.
Michelle:Yeah, we have our first class graduating this spring. We're really excited.
Sarah:And you guys are trying to be large animal focused, at least somewhat.
Michelle:The goal of the school is to produce practice-ready veterinarians to serve rural and regional communities. And so their fourth year is a distributive curriculum where they are out in clinics in Texas, a lot in the panhandle, some in Oklahoma, some in New Mexico. But it definitely we try and make them well-rounded practitioners. But we do have a pretty strong food animal group here. They get a lot of hands-on lab experience in the first three years.
Sarah:And they learn about cats and dogs also.
Michelle:They do learn about cats and dogs, yes. They have surgery labs with small animals, and there's there's animals on site from the local shelter that we spay and neuter and do behavior training and stuff like that. So, yes, I I'd say it's a well-rounded curriculum.
Sarah:Awesome. I know a lot of people have just been interested about how that's been coming because we heard about it for so long. So I just thought people might enjoy a little update. Yeah. Um, so let's jump in. We are talking about goats actually today. So some of Michelle's research is published, some is not. We're gonna kind of talk about it in like broad strokes about what she looked at. So jump in. What were what are we talking about today, Dr. Buckley?
Michelle:All right. So the title of the grant that funds my research was Improving Antimicrobial Stewardship in Dairy Goats to assure food safety and milk quality. And the project was funded by a USDA grant from the National Institute of Food and Agriculture's Agricultural and Food Research Initiative competitive program, which is specifically um focusing on antimicrobial resistance. So if you listened to season one of this podcast, you heard me read that information off after every episode. Or maybe before every episode. It's it's in there. We focused on subclinical mastitis in dairy goats specifically due to non-aureas staph during the dry period, and we targeted, we did targeted dry treatment using two different intramammary antibiotics that are approved in dairy cattle in the U.S.
Sarah:I think a lot of pet goat people may not understand dry treating. So in the dairy world, you know, we milk and then when they are two months away from calving, we we dry them off of milking, and that's their dry period. And so that usually consists of a tube of intermammary antibiotic that stays in there the whole time of their dry period, does not get milked out. And so it has a much longer acting job than something that if they are you're just treating them for mastitis during their lactation. Some people will also use a product that's almost like a plug. Is that still common? I've been out of the dairy circle for a while, but is is like the gel stuff still common in the dairy world?
Michelle:Yeah, that's a good point. So intramammary antibiotics are pretty common in dairy cattle, but the internal teeth sealants, I think that's what you're talking about. Yes. Some producers will use them and some won't. The complaint is that they hang around after the cow freshens and it can get kind of messy. So, yeah, some folks will use them in the bovine world. In the dairy goat world, I've never met a producer that used that.
Sarah:Yeah, they're getting close to we want them to have a dry period that's gonna rejuvenate their udder, make their next lactation much stronger, much healthier, much better. They just need a break. And we just want to make sure they go into that next lactation with the healthiest udder possible. So you looked at what I call the non-scary staff. And so I think everyone understands subclinical means they aren't sick. Right. So these bacteria are in there and they're they're not great, but they're also not causing a fever, not causing her to be off feed. So, but you want them to go into their neck lact next lactation healthy. So it's very important that we hit this if we need if it needs to be addressed. So that clears up hopefully dry period, dry treating, subclinical mastitis, just in case anybody's unclear about those topics. Okay.
Michelle:Yeah. Awesome. The tricky thing about the non-aureus staffs is yeah, they don't always cause that clinical mastitis like we tend to see with staph aureus, even though they can do both, just like staph aureus can do both. You can have your subclinical infections there too. But they're really good at like digging into the udder and getting comfortable and avoiding the immune system. So if they hang out there for the whole dry period and you're not milking the goat every day and potentially pulling those pathogens out, they're they really make themselves comfortable. And chronic infections can decrease uh milk yield, they can impact your components. A lot of times when you see like lopsided udders, which I feel like we see a lot in dairy goats, that's a sign that that smaller half of the udder was infected with a non-aureus saph or some other pathogen, but it's a sign that there was subclinical mastitis there and it hung out for so long that it basically eliminated a lot of the productive milking tissue and replaced it with scar tissue. And that's what those things do if they're allowed to hang out.
Sarah:So and I feel like a lot of people have that backwards. They think the smaller, tighter ones are the healthier ones, which is actually absolutely the opposite.
Michelle:Right. Right. And by the time that half of the other shrunk, like you really can't get that function back. So finding these infections early and treating them is really important to maintaining the productive life of the animal, really.
Sarah:Yeah. So how common are those subclinical infections, do you think?
Michelle:So subclinical mastitis is pretty common in dairy goats. Some studies have actually demonstrated up to a 50% prevalence on farms. And these are studies from all over the world. So management practices might be different that impact that prevalence. But most of the studies are going to report somewhere between 20 to 30% prevalence or maybe a little bit over 30%. And then non-aureus staphs is are by far the most common pathogen group associated with subclinical mastitis.
Sarah:Yeah. And some of those management stuff would be like bedding, you know, where they go for their dry period, genetics. There's all sorts of stuff that's going to affect the prevalence of subclinical on your farm. That's a whole utter prep. Yeah, that's a whole other podcast. Um okay, so let's jump into the drugs that you were looking at and give us a little intro. Just start us out with the two that you kind of looked at in these first studies.
Michelle:Yeah, so we only looked at Orbenin DC, which is cloxicillin, and then tomorrow, which is a Merc product. So Orbenin's a BI product. Shout out BI. We and then they they didn't sponsor this, but you know, thanks for making a dry tube. And then tomorrow was the other product that we use, which was a Merc product, and the active ingredient in that is cefapyrin. So I'm gonna refer to both of these drugs as their actual drug names just because we're not sponsored by either of the companies, and sometimes there are multiple products that have the same active ingredient. So the important thing is the active ingredient here. So both the cloxicillin and the cefapyrin products are formulated with a benzetane salt. So when you look at the label, you'll see the big trade name at the top, and then you'll see the active ingredient underneath. And so it's cloxicillin, benzithane, cefapyrin, benzithane. And that salt is specifically designed to make the product stay in the mammary gland for a longer period of time. So that's why we use these products for dry-off and dry period, and that's why we would use a product like today instead of tomorrow for lactating because the salt that it's formulated with doesn't make it hang around very long. So it has a shorter milk withhold.
Sarah:Right, exactly. Yeah. Okay. All right. So then let's jump into the study. Let's talk about obviously they were all does because does are who lactate. And so, how did you pick those animals? Give us a little bit about the like procedures of this first study.
Michelle:Yeah, so for all of the studies, the inclusion criteria was the same. The doughs had to be generally clinically healthy, two functional halves, no clinical mastitis at dry-off. We looked at farm records to be sure that all the animals that we enrolled in the studies had not received antibiotics within 30 days of enrollment because we didn't want anything else to potentially be in their system that would impact our results. And then animals in the milk residue study, specifically in the efficacy study, also had to have a target dry period of 60 days, but we allowed for a range of 50 to 90 days.
Sarah:Unlike a lot of the retrospective studies we've talked about in this podcast, these animals did not have mastitis. At least this first one, you you said something about the efficacy study, and that's later. This one wasn't look, we're not looking to see how how the drugs treated it. We're looking to see how long they stay in the system. Like we're looking at other things than tr actually treating mastitis right now.
unknown:Right.
Michelle:Yeah, right. And we'll we'll talk about it a little later in this podcast. But yeah, our first study was a pharmacokinetics study, which like I feel like everybody's eyes glaze over when I say the word pharmacokinetics. So I can abbreviate it PK, but really all pharmacokinetics means is we're just looking at how the drug moves through the body, especially how fast it gets out.
Sarah:So these does we specifically were you were specifically looking for healthy animals, not animals with mastitis. So that that was not the point of this. And that's how all drug studies work for humans and animals. You don't start with sick animals. You want to make sure that you know they're healthy first before we see how they how they work. Right.
Michelle:Okay. Yeah. So this study is called pharmacokinetics of long-acting cephipyrin and cloxicillin after intramammary administration in dairy goats. I know it's a mouthful. This one is published, and it was published in the Germ Journal of Veterinary Pharmacology and Therapeutics earlier this year. So yeah, it's a little bit technical, but we'll try and bring back the clinical relevance at the end of our summary.
Sarah:We're just gonna do the takeaways. We're not gonna get down into the mud. So, okay, so let's get into the details of the study. So you dried the doughs off, and then what'd you do?
Michelle:Yeah, so we had 12 doughs in each treatment group. 12 doughs got saphiran, 12 doughs got cloxicillin. We gave each dough a full tube in each half of their udder, which is really important. When you in practice, when you are dry treating or administering mastitis treatment to any dairy animal, you should be using a full tube. And I know a lot of my dairy goat producers in practice wanted to use a half because it's a smaller animal than a cow, but you should do a full tube because all of the studies that we do are full tubes. So and their udder is actually like not that much smaller than a cow.
Sarah:Solid point.
Michelle:Anyway, yeah. We treated all 24 doughs, and then we just collected blood samples. So the goal of the study was to actually look at what the drug was doing inside of the animal's circulatory system in the blood, if it even got there from the udder, and then how long it took to get out. Because this is a really easy study to do. It doesn't require a lot of intensive sampling or sacrificing of animals to collect tissues. You're just drawing blood. And we did that for a week to just get an idea of how long the drugs are hanging around.
Sarah:Were they all the same breed?
Michelle:We had a mixed bag. We had mostly saunens and alpines just because of the farm that we were able to find to work with.
Sarah:But similar size. It's not like you were having Nigerian dwarfs and similar size dairy breeds. Okay. Okay, so this was kind of a straightforward blood draw, not too bad. So, what it what was the takeaway on this study?
Michelle:So this study actually surprised us. And we did this study. We didn't actually do the study chronologically first. We did this study because we ran one of our tissue, our meat studies first. Uh, and we were really confused by the results because we couldn't find one of the drugs. So we were like, okay, we got to get a better idea of what's going on. Let's do a PK study. So this study actually gave us a better understanding of why we got weird results on that meat study because it showed us that the drugs aren't acting the same, even though they're both formulated with that benzethane salt. The cefapyrin product, that tomorrow product, actually was getting out of the system a whole lot faster than the cloxicillin. So, for example, just to give you an idea of how different the drugs were, the average half-life of cefapyrin of tomorrow in these goats was seven hours. And the average half-life of cloxicillin was 77 and a half hours. Yeah.
Sarah:Which is bad, right? We want it there for a long time. We want it to cover them through a lot of the dry period, correct?
Michelle:Yeah, it is interesting because the cloxicillin, the orbenin product, does have a prevention label, which would mean that the drugs hanging around long enough to like keep bacteria from becoming a problem during the dry period, not just curing infections that they have at the start of the dry period. We can get into that a little bit more later. Okay. So interestingly, even though they didn't get out of the body at the same amount of time, they actually both reached about the same concentrations. And it just took the orbenin a lot longer to leave the system than it did the the tomorrow, the cepapyrum product.
Sarah:Okay. So this PK study, you went back and you just you learned very quickly that how long they kind of how how long it takes them to peak and how long it takes them to leave the body.
Michelle:Correct. The thing about a PK study for an intrammary treatment is that the memory gland is kind of selfish. It wants to hold on to the drugs that you put inside of it and it doesn't actually let a lot of that drug out into circulation. So this was just kind of a roadmap for us. It was just a guide to help us plan how we were going to schedule our follow-up studies. So we knew we would have to sample longer for the cloxicillin and that the cephipirin, we needed to make sure we were getting some good sampling points early in the study so that we didn't miss it.
Sarah:Yeah, that's important. But I mean, obviously, when you think about it the other way, saying that the mammary gland is selfish, it keeps it in, it also keeps things out. That's why we have to treat mastitis intramammarally and not parental, right? So the road roll runs both ways with the mammary gland. It's like don't come in and don't come out.
Michelle:Right. Yeah, it's very protective. Yes, that's a great point. We sometimes will use systemic treatments for mastitis if the animal is like clinically systemically ill. But yeah, the mainstay, especially of like mild mastitis treatment, should be intramammary.
unknown:Yeah.
Sarah:I mean, it does interact with the body, it's not a completely separate entity, but it doesn't want to interact as much as some of the other organs for sure. Okay, so check on that study. Are we ready to move to the next?
Michelle:Yes. All right. The next study that we ran was the tissue residue study, which I kind of mentioned already. This was the study where we were trying to determine meat withdrawals. So to do that, we have to dry doughs off again, and then we let these doughs hang out. So the first study that we ran, the first tissue study that we ran, we let these doughs hang out for 21 days. So three weeks before we sampled anybody. And during that study, we sacrificed four animals from each treatment group. So eight animals every week from 21 days post-treatment all the way out to 49 days. So it was basically a month of sampling once a week. And when we got the analysis back from our analytic chemistry group, we actually didn't find any cefapyrone in any of the tissues at any time. It was just gone already. And the cloxicillin was pretty spotty too. The last residue that we identified was 35 days post-treatment, and that was only in half of the livers. We weren't finding it in muscle or kidney at that point. And those were the three tissues that we sampled. So that was kind of where we started. So then we did the PK study, and we're like, okay, let's go back to the drawing board. We need to do another meat tissue residue study and let's plan it out a little differently. So we knew we had captured the long part of it, but now we had to do the short period right after treatment so we could make sure that we were getting a better idea of what these drug concentrations were looking at early on. Um, so for the cefapyron animals, we needed more data points. So we actually sacrificed three doughs that were treated with cefapyrin one day after treatment, two days after treatment, four days, and then six days post-treatment. And then we needed a little bit more information on cloxicillin. So we only sampled three animals for that at three days post-treatment, and then three more animals seven days post-treatment.
Sarah:Okay. Yeah, this has got to be something that Farad's gonna be like. It's so awesome to have more information to you.
Michelle:I really hope so. That was that was really the goal of this study. Uh to get that information.
Sarah:I know I've talked about Farad in previous podcasts, but just for anyone that doesn't know, Farad is the organization that. That when we're not sure about a meat withhold or milk withhold or an animal gets a medication it shouldn't have, or we're using something off label, they're the ones that paw through all the research about that drug and give us a milk and meat withhold. And so they're a great resource for veterinarians to help keep the food, the animal food products safe for consumers. So I don't want to just throw that out there without people understanding. But so Michelle is one of the pe Dr. Buckley is contributing to the research for them to use. If you know someone's like, oh, I just ate my goat that I just dry treated. Am I okay? And it's like, well, hopefully you use tomorrow.
unknown:Right?
Michelle:Yeah, yeah. And Farad does a really awesome job of staying current on the literature. I see on Facebook all the time. People are like, does anyone know the withdrawal for this drug? And it, I always just want to be like, use the other F word, not Facebook. Go to Farad.
Sarah:And you're free. It doesn't cost us anything. It's just an email. It's really easy to do.
Michelle:Your tax dollars pay for it. You should use it. It is much more academic than Facebook. And they're updating the recommendations all the time. So that's why, you know, some some recommendation that someone got six months ago may not be relevant today.
unknown:Great.
Michelle:So that's my plot for Farad. Thanks for doing what you do. You go. Okay.
Sarah:So now we're on to the second meat study where we're wanting to see shorter instead of starting longer.
Michelle:Yep. Yeah. Okay. And so basically that study for the cefapyron dose, we still didn't find any cefapyron in any of the tissues at any time point. Even 24 hours after they were treated, we were not finding that drug in muscle, liver, or kidney. So it is either not getting into those tissues at measurable levels, or it's getting in and getting out so quickly that we didn't find it. So then the cloxicillin, we got a lot more data on that. And I think based on that study, we were pretty well able to characterize the tissue residue depletion of that drug in dairy goats. So we can't make any recommendations as far as withdrawals go, but I'm really hopeful that Farad will be able to. And my general guess is that they're gonna say that cefapyrin probably needs a shorter meat withhold than the cloxicillin product.
Sarah:And so I think this is something that practitioners can even take away right now.
Michelle:I would say generally, if you have your choice between like cephapyrin type product or the cloxicillin product, at least the long-acting products, it does seem like the cephapyrons leaving faster. So if you're really worried about residues and getting them back in the tank as quickly as you can, then that might be the product to go with. But also we know there's concerns with like availability. We'll get there, right? Right. Hopefully.
Sarah:Okay. So the milk study.
Michelle:Yeah. So with that, we treated 22 animals with each drug, and then we let them go through their dry period. So unlike the tissue study where we were sacrificing these animals, the milk study animals just got to go back into their herd, and we actually did these samples on farm at a commercial dairy. So they went through their dry period, and then once they started kitding, I was there at every milking to milk them into a separate floor pail individually and then collect samples from each dough. And we actually tested the milk on farm using a commercially available assay just to give us an idea of like, okay, does she still have detectable levels of residues, or are we maybe getting below that, below the bovine tolerance levels anyway, since that's what those tests are uh set up for. And then we saved the rest of the milk and sent that into our analytic chemistry lab where they can do much more accurate evaluations and detect drugs at much lower levels than those on-farm tests can. And so we actually use that when we were presenting data in our study, but the commercial test was just so that we had an idea of how long I needed to stay in a hotel and milk goats twice a day for while I was five months pregnant. Oh my. Good times, good times.
Sarah:Yeah, yeah. Okay. Well, you know, and I it's always nice because then this helps you validate those on farm tests a bit, right? So this is just one more way of being like, you know, because this is a great way for producers to be like, Am I gonna dump this milk because I accidentally, you know, milked a hot goat into it? Um, so there's no reason not to have one more way to validate these on-farm tests, right?
Michelle:Yeah, I mean, so my pharmacology hat's gonna come out right now when I tell you that the on-farm tests are not as accurate as the lab tests. And so we know that.
Sarah:Like everybody knows that, yes.
Michelle:So the tolerance is zero, right? And that's based on the lab tests.
Sarah:Yes, as well as should be nobody wants to drink antibiotic milk.
Michelle:Exactly, exactly. So even though we have a tolerance that is above zero in cattle, that's not the same for off-label use. And so the tolerance is zero for these guys. So you're you're not gonna be able to detect all the way as low as you could on the lab test, but also most processors are using these commercial tests, so it's probably an accurate estimate for producers. And honestly, the difference is, you know, parts per billion at this point. So these are really, really tiny numbers that we're talking about.
Sarah:But they do run some through mass specs, so don't get comfortable.
Michelle:Yeah, don't get comfortable. That's what Fear Ad is for. You should still be following their recommendations, but also it's always a good idea to test doughs before you start milking them back into the tank, even if you've gone through the whole withdrawal period and everything.
Sarah:Yeah, right. Exactly, exactly. Okay, so what'd you find?
Michelle:So it was a pretty similar story to the PK and the tissue study. We only found residues in three out of the 19 dose that were treated with cefapyrin and actually made it through the whole study without needing any other antibiotic treatment. And the last residue that we found in the cefapyrin dose was at 60 hours post-kidding, so two and a half days. We found cloxicillin in 11 out of the 21 dose that completed the study, with all but four doughs having undetectable residues by 48 hours post-kidding. So most of the doughs were done shedding by 48 hours, but we had a couple hanger oners. And one dough actually was positive for 14 milking. So she was positive for a full seven days. And we stopped sampling her after those seven days because everybody else was negative, and it just wasn't really feasible for me to stay at the hotel or drive two and a half hours out to the farm and then stay there for the day and then go back. So yeah, it just really didn't make a lot of sense for us to continue sampling her, but she hung on for a while. So we had a much bigger spread of data again. I think this is going to be reflected in the withdrawals that Farad will come up with, but I don't know what those will be.
Sarah:How much do you think? And if this is a dumb question, cut it out, Michelle. But how much do you think the fact that they were getting milked when we were dry treating them affects it? You know what I mean? Because normally you put it in there and you're not milking them.
Michelle:No, we didn't we didn't milk them right after they were treated. They went through their dry period and then we started milking them when they kitted, like you normally would.
Sarah:Normal lactation. Okay, so it had already been in there. So that's why it was out so fast after you okay.
Michelle:I think it's a really relevant question, and a lot of it sometimes that like doesn't come across. I don't communicate that very well. So thank you for asking a very helpful question, Sarah.
Sarah:Okay. So we've looked at how long it's in, and so now I think this is the most interesting part, the ethicus stuff, right? This is what's next. So so let's jump into what's working and what's doing a good job.
Michelle:Yeah, yeah. So this one also is in for review right now. So hopefully we'll be able to share it with you all in a published version in the next year. I don't know. Sometimes it takes a while.
Sarah:That's how research works. That's fine.
Michelle:We were looking to evaluate pathogen prevalence on three commercial goat dairies, and we also wanted to evaluate how effective these two drugs were for curing non-aureus staff subclinical mastitis compared with not treating that subclinical mastitis. Um, so the dairies we worked at were in California, Iowa, and Wisconsin. You know who you are. Thank you for being awesome. We loved working with all three of you.
Sarah:Um three of my favorite states. So I love it.
Michelle:Yeah. We did it for you, Sarah. That's really how we played with it. We also factored in the fact that these three states are the three highest, have the three highest population of dairy goats in the country.
Sarah:I didn't know that of Iowa. So interesting.
Michelle:Yeah, it's number three. So, and it worked out really nicely because we collaborated with UC Davis on this project. So they collected our California samples, and then I was driving to Wisconsin once a week to milk books. So we sampled every eligible dough. So those eligibility criteria I talked about at the beginning at the beginning, a week before her scheduled dry-off. And we that means we cultured, we collected milk from each half of her udder and cultured it. Anyone who had at least one half that was positive for non-aureus staff, and we randomly assigned them a treatment of either cefapyron, cloxicillin, or no treatment. If the dough only had one infected half and the other half didn't have a pathogen, then we left that half untreated as a negative control, but we kept it on the study. So we tracked what was going on in both T's. If she was infected in both halves, she got a full tube of treatment in each half. Okay. Makes sense? Yep. Cool. So they were allowed to go through their normal dry period per farm protocol, just like the milk residue study. And then once they kitted, we collected another milk sample for culture within the first seven days after she kitted. And then we followed them for 120 days in milk to see if any of them developed mastitis or died or were culled. And we also tracked milk production and somatic cell score via DHI testing during that period.
Sarah:So this is such a huge, awesome lesson for everyone to take away. Targeted dry therapy. So everyone doesn't get a tube. Those that need it get it, those that don't, don't. So going back to being good stewards of the antibiotic world, this is something that everybody can do on farm, right?
Michelle:Yeah, yeah. It it can have its challenges as far as management goes. If you're not used to separating treated and untreated doughs as they come fresh, it can be a bit of a challenge. And we need to have some different modes of identification. So, like collars or leg bands, which we all know goats are really good at getting rid of, but also keeping them in separate pens, which they're really good at jumping out of. So it's a little bit more of a management challenge than in cattle, where they will very willingly keep their leg bands on. I mean, not all the time, but most of the time. And they stay in the pens that they belong in, usually, not always, but much less of a problem. So yeah, I do want to emphasize that we recognize there are some management challenges that go along with ensuring that we aren't getting residues in the milk supply and keeping treated animals separate from non-treated animals until they're supposed to go back. But yeah, this should be the goal is targeted dry therapy for those that have a pathogen that we know is likely to be susceptible to the drugs we have available, which is probably non-Orea staff if it's a goat.
Sarah:Great, great. So did it do it? Did our non-scary staffs die?
Michelle:Yeah, yes. So just to talk about the prevalence for a second. So we sampled just over 1,500 halves, and uh just under 60% of them did not have any growth, and 39% were positive for non-aureus staffs. So we only found 16 staph aureus halves in that whole sample population, which I was pretty impressed by. I expected the prevalence to be higher. We had a couple of other pathogens, some streps, a carinibacteria, a moraxella, but vast majority was non-aureus staffs. And we found that our randomization worked, which is great because that was my job. But we had a pretty even distribution of pathogens across the treatment groups. So we felt good that there wasn't really any bias in that part of the study. Perfect. Good, good.
Sarah:Okay, so that's a good, a good representation, I feel like. Some were infected, some weren't, some had different pathogens. So Right.
Michelle:But yeah, it gave us a good idea of what we are seeing on commercial goat dairies in the US because a lot of the data that we have on this stuff is international. And so it's always good to know what's going on in your neck of the woods.
Sarah:Yeah, that's true of all our small ruminant stuff. Right. It's like, oh, look at this, no, that's the UK. Oh, look at this, no, that's Australia.
unknown:Yeah.
Michelle:Still relevant, but it's good to confirm that this is what's happening here too.
Sarah:Yeah, except they have very different legal drugs.
Michelle:So that's what That's also very true, yes.
Sarah:Especially when you live on the Canadian border and your colleagues are in a different country.
Michelle:That's wow, geez, I didn't even think of that.
Sarah:Anyway, continue side note.
Michelle:So yeah, your original question was did the drugs work? And yeah, they were pretty effective. Cefapyron had an 85% cure risk, and cloxicillin was just under it at 81%. So those were, as far as statistics go, like those are the same. So then when we look at our untreated HABs that had an infection, but we didn't do anything about it, they only cured 54% of the time. So that was a significant difference. And I think it's important to note that the drugs that we used are like first generation cephalosporin. That's what cefapyron is. So it's kind of a wimpy drug. It's not very broad spectrum, but it got the drugs that are the most common problem. And the cloxicillin is a penicillin, but also relatively wimpy, not very broad spectrum. So we don't need big gun antibiotics to be dealing with these subclinical infections in the vast majority of these cases.
Sarah:And by big guns, we mean spectromass. We need we mean the ones that are really hot and heavy, then you don't need those just because that's what your dairy farmer friend loves to use.
Michelle:Yeah, we don't need to throw shade, but you don't need spectromass right away. So especially not for subclinical infections. Right, exactly.
Sarah:Yeah, these goats aren't even sick. Right.
Michelle:Right. Let's save the big guns for a more intense infection or maybe something that we aren't having success uh treating with our smaller guns.
Sarah:Okay, so target therapy is working. Are these goats getting reinfected? That's probably something to talk about, also.
Michelle:So these intramamory antibiotics don't actually have like a preventative capability. That's more where we would use those teat sealants, the internal teat sealants to prevent new infections. So, really, the the purpose of this study was to look at cures, but we did to keep track of new infections. And the new infection rate for each of the drugs, cloxicillin was 25%, cefapyrone was 27%. So both of them did have some level of reinfection, but nothing, they weren't significantly different. The new infection risk for untreated halves was 32%, and that was not statistically different from the two treatments. The p-value was 0.99, and we're looking for anything smaller than 0.05. So there's no preventative qualities that we could identify for these products, at least in dairy goes.
Sarah:Are you surprised by those since one stays in so much longer? Was that a surprising outcome?
Michelle:That's a good question. But when I think about how the drug stays in the body, it's still at decreasing levels. So just because we can measure it doesn't mean that it's at a level that's gonna effectively act as an antibiotic. Okay. So yeah, it makes sense to me. And then when we looked at those halves that were not infected at dry-off, but were associated with an infected half, so they were attached to a goat that had an infection on the other side of the udder. Um, those actually had a 35% risk of developing an infection during the dry period. So even if they weren't infected originally, they could become infected. And again, that wasn't different from any of the other treatment groups. So everybody's at an equal risk.
Sarah:Interesting. Okay. I mean, that makes sense to me. That's that seems like a track. Okay, so let's talk about the infections that didn't cure.
Michelle:Yeah, yeah. So that funnels us into our next study, which looked at antimicrobial resistance and antimicrobial susceptibility. And also we did a little bit with virulence factors, which I'm not really going to cover too much because it wasn't the main point of the study. But we did have 34.6% of infected halves that had the same pathogen isolated at the two sampling points. So if it was staph caprae at dry-off, we cultured the same thing post-kidding. So we considered those to be non-cures. We also took those new infections. So whether it had a different species cultured at dry-off in post-kidding, or if it didn't have a pathogen at dry-off and then did at post-kidding, we took all of those and we used them for our final study. So the thought was that those isolates would be the most likely to have resistant features that we wanted to look into a little bit further and kind of figure out what those might be.
Sarah:Okay, so now we're gonna move on to what we're crawl calling antimicrobial sub susceptibility testing. Okay, now we're moving on to what we're calling antimicrobial susceptibility testing. That's hard to say. We'll call it AST. And so basically, we're trying to decide whether a bacteria will be killed by a certain ambiotic or not. So the bacteria is exposed to a bunch of different concentration of the various drugs during these kinds of testing, and we see how much of the drug that takes to kill it. So this is one way we come up with dosing a lot of time for our antibiotics. And so then this is based on data that connects those numbers to clinical outcomes, right? We get an idea of whether each of the drugs is likely to be effective treatment or not. So, I mean, this is super important as kind of the next step.
Michelle:Right. So when you susceptible when you submit culture and sensitivity data, they're using some methodology that's this or something similar to spit you back out that SI or R that shows susceptible, resistant, or intermediate. So for our purposes, we aren't giving you that SI or R in this study. We're just describing how things responded to the different concentrations of antibiotics.
Sarah:So if you're a producer and you have some any kind of infection that won't clear, your vet is probably gonna take a sample, send it to the lab, and they're gonna tell you which antibiotic is gonna work best for that infection. So if you've tried an antibiotic and it hasn't worked, this is usually the next step. And the results we get back from wherever we sent it will have the S, R, or, I. And so this is very common in vet medicine. A lot of the vets use it all the time. But as producers, this may not be something that you're seeing, but it's something very common for the rest of us.
Michelle:Yeah. And I will say that even a lot of veterinarians probably don't understand how much goes into giving you one of those three little letters as far as the data behind it. But I think the main takeaway that we need to understand is that the people who set those what we call breakpoints of does it qualify as susceptible or resistant, they're from a group called CLSI, the Clinical Laboratory Standards Institute. And they're really, really smart people and they're really good at their jobs. And they're always looking for new data that helps them to determine whether the concentration they see in the lab is going to correlate with a clinical cure in the animal. Unfortunately, they don't have breakpoints for pathogens in small ruminants. So they will give you an SI or R, but it's going to be based on data that's not from small ruminants. It's probably based on cattle or another species. And it's not always for the drugs that we are using. So that's my caveat about susceptibility testing. It can be a helpful guide, but I would say for small ruminant mastitis, it it may not actually be worth your while to submit for sensitivity. Culture, very valuable. Sensitivity at this point, I think you get as much information as you need from knowing the pathogen that you're dealing with.
Sarah:Okay. Okay. So, okay, so what are the drugs that you guys looked at for this?
Michelle:Yeah, so we used a commercially available mastitis plate for this lab susceptibility testing. So the drugs included in that plate were ampicillin, ceftieopher, which is that spectromast product, which is basically the equivalent of the cephipyrin product that we used, erythromycin, oxicillin, which is similar to the cloxicillin product that we used, penicillin, penicillin novobiocin, perlamycin, sulfidimethoxine, and tetracycline. So again, this was just a commercially available mastitis plate looking at drugs that are or were approved in the US for treating mastitis at one point. Okay. So when we looked at the test results, we use what's called an MIC, which is the minimum inhibitory concentration. So that's the lowest amount of drug required to kill the bacteria. And when we have MIC data for a group of pathogens and antibiotics, we can start using that data to track patterns. And we really didn't see any changes between the two time points. So we looked at dry-off and then compared them to the post-kidding samples. We really didn't have very many changes. We had a few drugs that actually decreased between those two periods. So it actually got lower. It took less drug to kill the bug on the post-kidding sample than the dry-off sample. And then only tetracycline increased its EC value. And that was increased from two micrograms per mil to four micrograms per mil. So not a huge increase, but we did see a small change. All of the isolates that we tested were inhibited at the lowest concentration that we tested for both cephalatin or the cefapyrin and the cloxicillin. So that seems to be killing them pretty easily in the lab. Doesn't 100% correlate with the conditions in the udder, but at least in a petri dish, they die pretty fast with those drugs on board.
Sarah:It sounds like that's a phenotypic evaluation where we look at how the bacteria responds to the drug. So tell me about the genotypic evaluation you did and how that ties in.
Michelle:Yeah, so we we took those same isolates and we sent them over to our genomics group at Iowa State and had them do whole genome sequencing. And then they look specifically for genes that we know are associated with antimicrobial resistance. And to make a long story short, we saw a lot of antimicrobial resistance genes within the population, both to beta-lactam drugs, which was the class we used, and other classes of drugs that we were not using on these GOATs. And there were actually two genes that were present in every single isolate that we looked at. One that conferred resistance to aminoglycosides and one to trimethoprim. But we only found one gene that was associated with resistance to beta-lactams, and that's the BLAZ, the blocky gene. Um, and it was only found in 45% of the isolates we evaluated. So there wasn't a good genetic explanation for why some of the why these infections didn't cure. So even though there's, you know, it could be that they didn't cure because of resistance, there it's likely that there could have been something else going on. So when we we compared the anicrobial resistance genes for those non-cured infections that had the same pathogen at both time points, and 44 out of 52 of those isolates matched 100% of their resistance genes. So they looked exactly the same. We think those are probably the same bug at both time points. Some of them didn't match though. And so the lowest matching percentage we had was 83% between time points, and we're not really sure if this dissimilarity is due to changes in the pathogen's genome. Like it is the same pathogen, but it it got some genes or lost some genes during the study period, or if maybe we did cure the infection and then the animal just happened to get reinfected with a different pathogen of the same species. So it looked like a non-cure to us because we were just looking at two different time points. Does that make sense?
Sarah:Yes.
Michelle:So does that mean that the isolates would have been resistant to the trimethoprim or the amino glycosides if you had tried to treat them with either of those, do you think the tricky thing about looking at genes only to evaluate resistance is that doesn't always translate into what the bacteria is going to do. It just means it has the potential to do that. So hard to say without actually doing the work, but I think that's one thing to remember if you do go diving into the literature is just because we say that something was resistant or had a resistance gene doesn't mean that that gene is turned on and functioning and impacting the way that the bug responds to the drug.
Sarah:Right. We're back to the genotypic, phenotypic constant battle. Okay, so that makes sense to me. I'm sure some people are glazing over, but that's okay. Stick with us. Okay, so that was a lot of pretty technical information. Let's bring it back around to a clinical level to make it relevant to our producers and listeners. Kind of give us the moral of your story here, Michelle, from your research.
Michelle:Yeah, so the moral of the story is we don't actually see much evidence of antimicrobial resistance development in non-aureas staphs that are causing subclinical mastitis with targeted dry therapy with either cefapyrine or coxicillin benzetane products in dairygos. And even the isolates that demonstrated phenotypic resistance behavior, where they, for our intents and purposes, didn't cure the infection, they didn't actually all have a genetic reason for it. And when we look at our susceptibility testing, none of them should have responded that way because they were all inhibited at very low concentrations of drugs. So that's why we evaluate things in several different ways. So obviously, this isn't a license to go out and use dry treatment all willy-nilly. We still need to adhere to judicious use principles and do our best to only be treating animals who actually need therapy, which will actually save producers money by spending less on drugs and having less animals with milk withholds that need to have their milk dumped. But also it decreases our concern about imminent resistance developing by using this therapy that we know is helpful for keeping goats healthy and extending their productive life within our herd.
Sarah:The two phrases I never want to hear with antibiotic use is kitchen sink and willy-nilly. Neither of those ever apply when you're using antibiotics. Okay, is there anything you want to add about your study? Did you feel like we checked all the boxes of you what you felt feel like is important here? I hope so. Yeah, we didn't. Yeah, yeah. This is this is so interesting. And the funny thing is, we just spent 40 minutes talking about like six years of your life.
Michelle:Yeah. Yeah.
Sarah:Okay, so so here it is, a wrap-up question that you hear every month. Um, so what do you see as the next problem that researchers need to think about and address in our small ruminant medicine? Remember, shoot for the moon or focus on what you love. It's up to you.
Michelle:Yeah. Oh gosh, there's so much room for more knowledge, small ruminants and camelids. I think even camelids need it even more. Obviously, with my pharmacology training, I think we need to have a lot more, a lot better understanding of how drugs are handled differently in small ruminant and camelid species versus cattle, which is what most of the data is on. And so looking at these clinical efficacy studies and residue studies, or even just pharmacokinetic studies, and there are some really awesome researchers out there who are working hard at getting some baseline information already. So, yeah, obviously we've got a lot of room to learn in pharmacology. Also, Rosie Bush mentioned vaccines when she was on here. And man, we need some more small ruminant-specific vaccines, especially for respiratory disease, Q fever, Q fever, yeah. There's there's plenty of things. Abortions, we we don't even have access to the vaccines that have been developed, and even those vaccines aren't super effective. So yeah, I think vaccines and drugs are are two tools that as veterinarians we reach for pretty often, and there's definitely a lot of room, which is job security for some of us. Absolutely, absolutely finding funding for those projects can be a challenge, but the USDA has really recognized the lack of information that we have and has really stepped up in funding more small ruminant specific projects. So I'm hoping that we'll get more useful data on a lot of this soon.
Sarah:Awesome. Yep. I think those are all great answers. There's there's so many things that can be the answer to this question because we still have such little information about so much of small ruminant medicine. Yeah. For sure. Well, I just want to thank Dr. Buckley for taking time out of her very, very, very busy schedule. She is about to defend all of this work. And so everybody can wish her luck. By the time you're listening to this, she may be done. So we'll be done. Whether it passed or not is another story, but I will be done. All right. So thank you so much for listening to the November issue of Boz and Bleats. And I hope you all enjoy your turkey day. Thanks, Sarah. Take care. Bye.
