So, you did fairly major intestinal exploration? For something else and this was incidental? I hope you didn’t do this looking for the ELs
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Sorry, I thought you were responding to my comment about my horse’s encysted small strongyles… The encysted small strongyles were found in a biopsy of the hind gut wall.
I was. And I’m now curious why a biopsy was done. I’m also still hoping that invasive biopsy wasn’t done for the sole purpose of finding ELs
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What are ELs?
Encysted larva? Just guessing?
I think you’re probably right given the context.
@JB Did we say “let’s do a biopsy to see if there are encysted small strongyles”? No. Were the encysted small strongyles what we were looking for in doing the biopsy? Yes. The biopsy was a “we tried everything else, maybe we’ll find something with a biopsy” option - and we found the encysted ones.
The horse must have picked up a lot of small strongyles at once, which must have had synchronized development for a while as fecal counts showed very low egg counts. We had ruled out worms early on (now I would repeat the fecal counts, but then we didn’t know) so we weren’t expecting the encysted ones. We then did another fecal and opted for the two step deworming when that one had a high egg count.
I mean, those are kinda the same thing - did you mistype? I will say this again: all horses are going to have a parasite load. Period. They are all going to have both encysted and adult small strongyles. Most anthelmintics (edit: I guess I shouldn’t say most, it’s really half considering that ivermectin and moxidectin are the only products that still work in most places) that still work don’t cover encysted stages, the macrocyclic lactones are quickly losing efficacy, and efficacy isn’t 100% for any of the drugs anyway. It’s very strange to me that a veterinarian wouldn’t expect to see any encysted larvae at all. It just doesn’t make any sense. There was no reason to even do a biopsy, just treat with anthelmintics. It’s cheaper and less invasive and very safe.
EL does stand for encysted larvae, and a fecal egg count doesn’t tell you anything about the number of encysted larvae, or even the amount of adults. A negative fecal egg count is simply “no eggs seen;” many methods have a detection limit of 25-50 eggs per gram so essentially the result is “less than 25/50 eggs per gram” - it does not mean there are no parasites present in the horse, or even that the horse is not shedding any eggs at all.
Not only that, but even a biopsy has some major issues, especially since you have to take samples from the proper location, and there is quite a lot of variance depending on where you take samples from even within the the same organ (see: https://www.sciencedirect.com/science/article/abs/pii/S0304401719301918). If the goal is a yes/no answer versus a quantitation, then it’s pretty safe to assume yes, there are encysted larvae. It would be pretty incredible to see a horse without any small strongyles present in their GI tract!
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This is part of our assumption, yes. Adult horses don’t maintain a population of ascarids, although they may be exposed in the environment, especially on breeding farms, yet they typically maintain immunity for life. Quite interesting, and we don’t really know why or how this happens, and it’s something that ought to be studied more closely. It would also be a very worthy study to compare the health of horses that grow up without parasites to an anthelmintic naive herd and a managed herd, but it would be ridiculously difficult, expensive, and unethical since the horse(s) would have to live in a sterile stall 24/7 for their entire lives. Plus there’s no way to confirm they are parasite-free until necropsy - could you imagine running a project for multiple years only to find out the horses somehow got parasites?! That would be horrible, hah. I would cry.
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No, I didn’t mistype. Did you stop reading? 
The sentence following what you quoted explained the difference.
We weren’t looking specifically for encysted larvae. We found encysted larvae. Dealing with them resolved the problem that had prompted the biopsy in the first place. So no, we weren’t looking for them, but they proved to be what we were looking for. Clear as mud? 
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Ah I see what you mean, the encysted larvae were what you were looking for in doing the biopsy as in that you found them, treated for it, and that solved your issues. It’s still interesting to me that your vet didn’t just go ahead and have you do an anthelmintic treatment just to cover your bases, despite seeing no eggs on the fecal. It’s a pretty harmless option, but I’m an academic, not a veterinarian, so perhaps they had a good reason.
Multiple fecals are always a good idea though! There’s a ton of variation caused by which bit of poo was grabbed, which subsample from that poo was used to do the fecal, who prepped the sample, how well they’re trained, and on and on. God forbid they forget homogenize the sample again before putting it onto the slide, because they’re probably going to get a negative result or an absurdly high result, depending where they take their sample from in the slurry. And remember: no eggs seen does not mean there are no eggs or that the horse doesn’t have worms, just that they aren’t contributing to infection pressure on the pasture (another interesting research question that we don’t know the answer to is why some horses are low shedders and others are not) 
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We had done the fecal, and the horse had been dewormed early on in the many month hunt, so we had already ruled worms out as a possible cause. It’s not surprising that the vet didn’t randomly order more deworming as that was the time of the transition to fecal based deworming from the rotational deworming method. There was a strong push to not randomly deworm as it would do more to increase resistance than to help the horse if it wasn’t necessary.
The biopsy really was a Hail Mary sort of thing. We weren’t expecting anything and even with the results of nothing abnormal, but there are a bunch of encysted strongyles the vet wasn’t convinced that they were the. cause. Given nothing else to go on we tried deworming for encysted strongyles and got results.
What I found interesting is that this horse was consistently a high shedder for a few years after this, but has become a consistently low shedder in the past few years. 
It can fluctuate with age. Typically we see younger horses shedding high numbers, middle aged horses moderate to low, and then they tend to increase again as they get older. It might be immunity, genetics, environment, worm species composition, microbiome, deworming regimen, or some crazy combination of all of the above! And of course, as with everything science, it’s not a hard and fast rule; some horses are low for most of their lives, others are high. It’s something I’m really interested in studying at some point in my academic career.
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My understnding is that the concern abou tQuest Plus is that SOME horses have a strong allergic reaction to the substance that makes it “gold”.
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I think it’s Zimectrin Gold to which a number of horses have had bad reactions. That dewormer is an ivermectin-praziquantal combo.
A while ago, there was a lot of concern (some of which was overhyped) about moxidectin causing bad reactions, particularly in foals and underweight horses.
There’s also been some concern with dewormers causing a huge die-off in worms that can then cause a bad reaction in the horse. Often (IIRC), that’s a result of the dying worms releasing a toxin as they die, and it’s that toxin that causes the reaction. But moxidectin paralyzes the worms and causes them to die gradually, which lessens the risk of a massive die-off in a short period of time.
Here’s a short review of moxidectin and how it works:
Review of the use of moxidectin in horses
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Isn’t equimax the same thing?
Same active ingredients, different carrier. It’s the carrier that’s a problem with Zimecterin Gold.
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I thought I’ve heard the dye is the issue with ZG? I’m not sure though, I use equimax instead.
For quest plus, from what my vet tech friend explained awhile ago is that most dewormers are tested to see what their “overdose range” is. Most of them you’d have to give them like 15-20x the recommended dose before you’d start seeing big problems. However, Quest plus has a lower threshold around 5-6x before you start to have problems so that’s why foals can have issues because they’re little and it’s just easier for someone to go way over the recommended dose.
Thanks you 
That makes more sense.
I agree! I need to ask some of my fellow parasite geek friends if they have run across any literature
So many things to be studied in horses just aren’t feasible 
