Equimax or Zimecterin Gold for Spring? I have both on hand and can’t remember which is better.
Quest Plus in the spring, Equimax in the fall. Never Zimecterin Gold–the carrier runs risk of chemical burns to the oral mucosa.
Quest Plus is kinder to the dung beatles that are more active in the spring.
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I alternate between moxidectin plus praziquantel and ivermectin plus praziquantel in the spring and fall. I’ve used Zimectrin Gold and never had a problem. Years of fecal tests show this regime is good for my horse, a former superspreader.
I do Moxidectin/Praziquantel in the fall (Quest Plus) and Ivermectin in the spring (I personally use Eqvalan Gold). Keep in mind minis cannot have Moxidectin so our mini just has Eqvalan twice per year.
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Ivermectin after the hard freeze for bots. And then fecal counts every few months to see if there is anything else to deal with. (I only have summer pasture so he’s in a dry lot most of the time, and I can’t recall the last time he got any other dewormer.)
I base my choice on fecals.
Generally horse, pony & mini get Equimax (ivermectin/praziquantel).
Given after Spring vax & fecal results.
Depending on load (if any), some get a 2nd dose 2 wks later.
Check with your vet for your area. Mine has me do the regular Quest (mox) in the spring.
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This is what we do.
What Simkie said
If you’re alternating Spring/Fall with ivermectin/moxidectin, please use moxidectin in the Spring and ivermectin in the Fall.
Ivermectin kills beneficial dung beetles, and they are most active in Spring and early Summer.
And yes, avoid Zimecterin Gold (Eqvalan Gold in Canada) - there’s no need to use it at all, when Equimax does the same thing without burning horses’ mouths, throats, and esophaguses (esophoagi? 
)
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I echo Simkie and JB. I never had a problem with Eqvalan Gold until I did, and it was horrible. The burns and inflammation took ages to subside, the whole side of her face swelled, and this was a horse who’d had Eqvalan Gold many times in the past.
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Omg?! I’ve never had problems with it that I know of and hadn’t heard of any either. It’s an expensive wormer tbh so I will have to look into that.
Just search in here for Zimecterin Gold in the subject line and you’ll find a few threads on this issue.
Quest in spring as well (west coast).
From a parasitology standpoint, it makes more sense to do moxidectin in the fall/early winter once temperatures are consistently low. This knocks down the encysted burden, which won’t have a chance to increase over the winter because the eggs are not larvating on the pasture once it’s cold. This of course isn’t relevant in warmer climates.
Ivermectin is rapidly losing efficacy (no really, we are working with a farm that has ivermectin-resistant cyathostomin populations - it’s here). For now moxidectin is the best bet anyway. They have the same mechanism of action though, so we’re getting ever closer to having zero anthelmintics that work. Yay.
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I would offer that if a horse has regular clean FECs, that an encysted colony isn’t a big concern. It’s true they can hang out for a few years until the time is “right”.
Resistance issues are a huge concern for sure. Ivermectin and even moxidectin have shortened ERPs now. Mox is the only real heavy hitter left, which makes it a good idea to not use it twice a year if you don’t have to. And given that the odds of an appreciable EL colony isn’t likely high for a horse with regular clean FECs (which is most of them), and given that the more we can let the environment take care of things, that is why I feel moxidectin in the Spring is the better choice, all else equal.
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This is incorrect. Fecal egg counts do not correlate to luminal parasite burden where cyathostomins are actively reproducing and releasing eggs, and they certainly do not correlate to the number of encysted larvae. The encysted stages are not producing eggs, and so a fecal tells you nothing about the number of encysted parasites.
This information has consistently been found in the literature and is why I am always adamant to point out to people that fecal results =/= parasite burden.
For example, in a larval cyathostominosis outbreak, only one horse presenting clinical symptoms of disease had a fecal over 200 EPG. All of the others were below the generally accepted treatment threshold - two wound up being euthanized.
Moxidectin and ivermectin are both macrocyclic lactones and have the same mechanism of action and drug target (glutamate-gated and GABA-gated chloride ion channels). Resistance to one will likely mean resistance to the other because ML resistance is generally believed to involve the drug target. This has been demonstrated on a farm where ML resistance to both drugs is clearly illustrated. That farm is absolutely meticulous about their parasite control program, which means ML resistance is likely far more widespread than we realize.
From the AAEP Parasite Control Guidelines (emphasis mine):
“Considerations for mature horses: Focus on control of cyathostomins. Depending on climatic conditions, one or two yearly treatments are sufficient to prevent occurrence of large strongyles. Consider including a treatment effective against encysted cyathostomins at a time when the mucosal burden is at its peak. Typically, this is more likely to occur towards the end of the grazing season, ie. fall in northern climates and spring in the more tropical and subtropical climates. Include a cestocide at least annually if they are a problem in your region.”
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I never said the encysted stages would produce eggs.
I said if a horse has regular clean FECs, the chances of a significant EL colony isn’t high. Why? Because while they can hang out for years, technically, the odds are that they aren’t likely to do that in an otherwise “clean” horse. And if you’re going to use Moxidectin in the Spring, does it really matter if a few ELs hang out over the Winter?
I also never said that egg counts are a direct correlation to the actual parasite load. But they are the best we have, and the leading parasitologists who have studied this for a couple decades have no issues with moxidectin in the Spring and ivermectin in the Fall
The link is good and people need to be aware of symptoms. But what was the deworming history of those study horses? That’s critical.
I realize the AAEP says to “consider” this protocol. They also say it depends on where you are.
“fall in northern climates and spring in the more tropical and subtropical climates.”
But if you’re in the North, and you use QP in the Spring (so in the May-ish timeframe assuming it’s warm enough), and it’s effective for about 12 weeks, you’re into August (or even maybe September if Spring was later and you dewormed later), by which time you’re hitting the end of grazing season.
Would it be ideal to use it in Sept/Oct in the North? Maybe. But then you’re going through Spring and Summer grazing with the potential for them to start building up, and wouldn’t that be a problem too:?
Fecal egg counts do not correlate to parasite burden - encysted or luminal. Just because a horse has a low fecal does not mean that it has a low number of luminal or encysted parasites. All a fecal tells you is how many parasite eggs that particular horse is contributing to pasture. Nothing else.
Paper #1
14 out of 23 horses kept in a pasture with high infection pressure and a questionable anthelmintic treatment history presented clinical symptoms of larval cyathostominosis. Only one of those horses had a fecal over 200 EPG.
Paper #2
Case studies where at least one horse (my academic subscription doesn’t work for this journal of course) presented with a negative fecal egg count, yet fecal smears showed larvae and the horse was diagnosed with larval cyathostominosis.
Paper #3
Horses presenting with larval cyathostominosis, many with negative fecal egg counts.
Paper #4
This study involved twenty horses presenting with larval cyathostominosis. All fecal egg counts performed at every time point during the study, including day zero, were negative.
It is certainly likely that some horses with low fecal egg counts have lower encysted burdens and lower parasite burdens overall, but that is demonstrably not always the case. This isn’t even something unique to managed horses. I’ve done fecals on feral horses who have never seen a tube of dewormer in their life who are negative for parasite eggs. Making an assumption that because a horse has a low fecal egg count, it will also have a low parasite burden, is simply incorrect.
I don’t have an issue with it either, but there is a reason why we recommend the opposite in general for much of the United States. The AAEP - made up of the leading equine parasitologists in the world - also recommends using this protocol for a reason. The idea is that horses are exposed to higher levels of infection pressure during the summer when more larvae are maturing to the infective stage and horses are grazing on pasture. In the fall, you knock down that encysted burden with moxidectin and it stays low over the winter since the larvae are unable to mature when it is cold.
It’s not a few encysted larvae hanging out over winter. It’s the largest mucosal burden, post grazing season, that is there over the winter. Treating in the spring does not prevent accumulation of mucosal parasites over the summer. That burden rises again over the grazing season, and is once again knocked down with a fall treatment. Again, just because your horse has a negative fecal egg count (which just means no eggs seen - most of them have a detection limit of 25-50 epg) does not mean there is not a parasite burden.
The currently reported egg reappearance period for moxidectin is about 12 weeks, but is starting to get much closer to around four weeks. ERP is the time it takes for eggs to appear in the feces again, not the amount of time where the drug is actively killing parasites. The prepatent period for cyathostomins is about eight weeks, so the infection is starting to build again within four weeks of treatment, or even immediately in some of these cases where we are seeing extremely shortened ERPs.
Yep. And they recommend treating when mucosal burden is highest. That would be at the end of the grazing season when they’ve spent an entire season gobbling up infective stages on pasture. In temperate climates, that is in the fall. In tropical and sub-tropical climates, that is in the spring. In climates without pasture, such as the southwest US and California, cyathostomins aren’t much of a concern. This article has good information.
I’ve participated in many meetings with many very large horse farms where we talk about their equine parasite control programs and make recommendations. Generally that recommendation is moxidectin/praziquantel in the fall and ivermectin in the spring. All I can do is state the science behind that recommendation. At the end of the day, it’s up to you and your veterinarian to decide what is best for your horse.
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