To worm on a schedule.....or not, I'm so confused!!! - The Horse Forum
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post #1 of 15 Old 06-20-2010, 12:05 AM Thread Starter
Green Broke
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To worm on a schedule.....or not, I'm so confused!!!

Now that I have a horse again, and I'm getting back into the swing of things, so to speak, I have been noticing that horse trends are definitely NOT what they were 10-15 year ago. I remember the kids at our stable showing WP wearing adorable little vests over tuxedo shirts with coordinating chaps, boots and hats...all coordinating with their saddle pads. Sadly, it seems those vests and chaps are gone in the WP show ring and so it would seem...are worming schedules?

I figured with all the new changes there were probably changes to newer and more improved dewormers. So I started doing some research to figure out a new schedule as I can't even remember the schedule I did use. It was Zimectrin, strongid, then something else...what was that??? Anyway...(I guess I started babbling), I found a lot of research online that says NOT to worm with dewormer on a schedule anymore because parasites are now building up an immunity to the dewormers??? I found 10+ articles, all by vets that say it's best to send your horsie's apples in for a spin cycle at the vets and they will tell you what parasites (if any) to treat. If they find nothing, you do nothing and you ONLY treat what they find.

So...what is your opinion of this? Do YOU still treat on a cycle, or treat the new way and why? Or do you have another plan that works even better for your horses? I have given thought to the feed through but my horse is in what I like to call a "public co/ed pasture" and I heard it only works if all the horses get it. I could be wrong. I also heard this also causes the parasites to build up resistance, but if that were true why do they have it??

Thanks for your opinions guys....
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post #2 of 15 Old 06-20-2010, 12:19 AM
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I only treat when I need to!

Honestly, its cheaper and less of a hassle. Instead of worming every other month, each time spending 20 bucks plus the gas to go and get it, and then trying to remember which wormer for which month, you go at the beginning of each season, spend spend 10-30 dollars on a fecal egg count (mine costs 20) and then the vet tells you EXACTLY what to go out and buy.

Its like on House, when they have no idea what the patient is sick with. House always prescribes "broad spectrum antibiotics" and then they would have to experiment with taking the patient off of each individual antibiotic till something goes wrong. Worming for a parasite that your horse may not even have is like the antibiotics. If House would just have his epiphany a little sooner, he could save himself a lot of grief.
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post #3 of 15 Old 06-20-2010, 12:34 AM
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I just do what my vet tells me to do. I also think it depends on if you board your horse or have them at home.

So far my moms horse has not been able to get rid of her worms, she has done two power packs since Jan. She is infested with round worms which is unusual for an adult horse. Luckily my friend and my horse were infested also but the power pack worked, and i haven't wormed my horse since jan. had a fecal tested and it was neg. He doesn't show any signs like he did before. My moms horse on the other hand, colic, bloated, and actually passing worms... gross.

I would get a fecal done, and talk to your vet about what he thinks your worming schedule should be. The worms are becoming resistant and i've talked to my vet and another vet my horse sees for his tumor,and he says the same thing, it's getting harder to deworm our horses, and we need to change what we are doing.
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post #4 of 15 Old 06-20-2010, 12:37 AM
Green Broke
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Have your vet to a fecal count on a fresh poop pile (not that expensive) and your vet can tell you exactly what your horse needs. I used to use the worming schedule through Pfizer and come to find out recently it's not very good for horses at all.

Your vet can come up with exactly what and how often your horse should be wormed.

Unless it weighs a ton... it's just a horse. Draft horse motto.
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post #5 of 15 Old 06-20-2010, 11:02 AM Thread Starter
Green Broke
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I agree and I think this is what I am going to do even though I think according to my boarding agreement I have Cinny on a schedule. I am going to use the stable's vet and ask him about it as well, that may just be an old contract that hasn't been updated to their vet's standards. I just really want to see what everyone else out here does currently. It seems so far the consensus is to "spin apples, then treat" am I right??
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post #6 of 15 Old 06-20-2010, 11:48 AM
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First, understand that you should always involve your vet in planning your deworming program and that's even more important now because strategic deworming should be done rather than following the old "deworm every 6-8 weeks rotating dewormers" which will no longer provide effective protection for your horse and will only help to build resistance. Along with the development of resistance is the fact that we now know that 20% of horses carry 80% of the parasites and those are the ones that need a more stringent deworming regimen while the other 80% of horses will need less frequent dewormings because they have a better resistance to parasites and thus don't carry big burdens even without frequent dewormings. . Add in the fact that environmental conditions vary all over the world and they have a direct affect on environmental contamination with parasite larve and on when infection rates are going to be highest in each situation. All of these facts mean that there is no "one-size-fits-all" deworming program. Some horses may only need deworming twice yearly while others like foals require much more frequent dewormings. So, rather than just following the old plan it's now recommended to practice strategic deworming--plan a program based upon the specifics of each horse and use diagnostic testing to ensure that the program is appropriate or to determine when deworming is necessary. This is to help reduce the number of dewormings to help slow the development of resistance while still providing adequate deworming for each horse. This is important because there aren't any new deworming drugs that will be hitting the market anytime soonIt is important to take all factors into account and know which horses are more resistant and which are less resistant in order to plan a deworming program that is going to be effective for minimizing parasite loads, minimizing the frequency of treatments and also minimizing the risk/rate of parasite resistance developing to the drugs in use.
So, rather than just following the old plan it's now recommended to practice strategic deworming--plan a program based upon the specifics of each horse and use diagnostic testing to ensure that the program is appropriate or to determine when deworming is necessary.
There are 4 classes of dewormer on the market:
benzimendazoles --fenbendazole, oxibendazole, other chemicals that end in -azole (there is a long list)
pyrantels---pyrantel pamoate (paste) and pyrantel tartrate (daily dewormer)
avermectins---ivermectin and moxidectin

Of those 4 classes, all but praziquantel are "broad spectrum" meaning that they kill several types of parasites. It is not necessary (or at least was not prior to the developement of parasite resistance) to rotate dewormers using these products to kill the most common parasites of horses. The "rotate to kill the different types of parasites" was necessary when we only had the much older drugs which were often only effective against one or two types of parasites. Praziquantel is the only one of the current drugs that is not broad spectrum and it kills tapeworms which the other drugs are not effective against unless you use pyrantel at twice the normal dose.

But, these drugs are not all as effective as they used to be because they have been over-used and mis-used for many years. Now we have parasites that are becoming and have become resistant to these drugs so we have to change our deworming strategies to help slow the build up of resistance while still minimizing the parasite load in our horses.

When planning a deworming program for adult horses, your main concerns are strongyles, tapeworms and bots in that order. (And this is where you can really see the big problem with deworming based on that link above.) Strongyles are the parasite with the most resistance issues--in more than 90% of areas tested these parasites are now resistant to fenbendazole and in more than 40% they are resistant to pyrantel. There has even been 1 study showing strongyles becomeing resistant to ivermectin. So, the standard rotation in that link you are likely not going to be effectively killing strongyles for 1, maybe 2 and even as many as 3 out of 3 dewormings.

For foals, your main concerns are ascarids, strongyles, tapes and bots. So you have the same concerns as with adults---resistant strongyles, but you also have the added concern of ascarids which are shown to be resistant to ivermectin in some areas of the country. Rotating is still a good idea in foals so that you balance possibly not killing ascarids with one treatment and then the next treatment killing ascarids but possibly not killing strongyles. However, it's probably best to stick to rotating either pyrantel or fenbendazole with ivermectin.

So, rotation options are limited at best and it's really not the rotation that is most important for preventing parasite resistance but appropriate dosing and treatment intervals.

You need to be SURE you are not under dosing your horses so always use a weight tape or measure your horse and calculate his weight. In studies even many vets were way off on weight estimations and they have the benefit of spending a few years working in situations where they get to walk horses onto scales daily to see what 900 lbs LOOKS LIKE.

Weight calculation information:
Body Weight Estimation of Horses KG calculation shown as well as a chart based upon heart girth measure (remember, the heart girth only assessment may be off by as much as 200 lbs just like weight tapes)
Horse Weight: Estimate It Easily How to calculate in pounds

For 40 years now, veterinarians have recommended that horses be dewormed every 8 weeks all year round and rotation of dewormers has been recommended for nearly that long. This is considered by many vets and horse owners to be “the recipe” for adequate and appropriate deworming of horses. However when you look at the research that has been done in the last 15 years you really have to question this practice. “’The recipe’ no longer represents an acceptable program for strongyle control” according to Dr. Craig R. Reinemayer, DVM, PhD of East Tennessee Clinical Research, Inc during a webinar presented via This means that deworming recommendations for adult horses need to be reconsidered because strongyles are the only significant nematode pathogen of mature horses. Continuing to use the same old deworming program will likely lead to heavily parasitized horses and further drug resistance. Instead, each horse and each situation should be evaluated to determine the reinfection rates and an appropriate deworming program for the individual.

It's now known that all adult horses living in the same situation do not necessarily need to be dewormed on the same schedule. 50% of horses in a herd will control parasite loads on their own due to natural resistance. Only about 20-30% of horses carry heavy parasite loads.
Thus each horse should be dewormed based upon an understanding of his own personal resistance to parasites. The best recommendation is now 2-4 dewormings a year based upon knowing which horses carry lots of parasites and which tend to carry little parasite load.

Cindy D.
Licensed Veterinary Technician
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post #7 of 15 Old 06-20-2010, 11:50 AM
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Rotational deworming is no longer an adequate or appropriate deworming program for adult horses. There are too many issues with strongyles developing resistance to 2 of the 4 most commonly used dewormers on the market---fenbendazole (more than 90% of areas tested have resistant strongyles) and pyrantel (around 1/2 of areas tested have strongyles resistant to this drug). And resistance is starting to be seen in strongyles to ivermectin---1st study showing it was done in KY in the last couple of years.

All adult horses in the continental US/Canada should be dewormed spring and fall with ivermectin/praziquantel or moxidectin/praziquantel. Other than those 2 standard dewormings, the rest of the deworming program should be based upon location and the horse's own resistance to parasites. The new recommendation is 2-4 dewormings per year based upon fecal egg counts used to determine the normal amount of egg shedding each horse does during the time of year when the weather in your area is most conducive to strongyle larva development and environmental survival. In the northern states in the US and in Canada, this means running a fecal egg count in the middle of summer (3 months after spring dosing if you used ivermectin or 4 months after spring dosing if you used ivermectin). In the southern US and Mexico you would be looking at testing in the middle of the winter (same time after spring deworming as listed above). Then based upon the number of eggs per gram of feces you can determine if you need more than the spring/fall dewormings and if so if you need 1 or 2 more dosings.

In the northern US and Canada, deworming should be discontinued during the winter months because the environmental conditions are not conducive to reinfection---that time of year has been proven to have extremely low reinfection rates. In the southern US and Mexico the opposit is true....deworming can be discontinued during the heat of summer because temps over 85 degrees lead to the infective strongyle larva dying quickly in the environment so the reinfection rates are lowest then.

For more detailed information check out the deworming webinar that was aired via The Horse magazine's website in April. Be prepared to sit for a while because it is an hour long presentation, but it's well worth the time. The veterinarian gives you all the information on strongyles and deworming in adult horses that you've always wanted to know and then some. It is a wonderful lecture. (And have plenty of paper and a pen.)…
(Craig R. Reinemeyer, DVM PhD --parasitologist)

When you are looking at testing fecal samples, you need to be having Fecal Egg Counts rather than fecal floatations (what most vets run) performed so that you actually get useful information. This is for 2 reasons:
1. fecal floatations are less accurate and you can easily end up with false negatives.
2. you need to know the number of eggs in a specific amount of sample to help determine the need for deworming.

You also need to know when to collect a fecal sample or you may get falsely low or negative test results because you are sampling too soon after your last deworming. The egg reappearance periods of the drugs on the market are important information because if you test within the egg reappearance period you are likely to get a negative or extremely low result simply because it's too soon after you dewormed to have adult egg-shedding parasites but you could very well have lots of immature parasites. So you get a false sense of security.

The ERPs for the commonly used drugs are:
fenbendazole and strongid--4 weeks
ivermectin--8 weeks
moxidectin--12 weeks

And then you would want to give at leat 4 weeks after that period before you collect samples so that you actually get a good idea for the kind of load your horse normally carries. This is very important because horses that have a good immunity to parasites won't need as frequent chemical deworming while those with low resistance will need more frequent dewormings.

Besides deworming, there are pasture maintenance practices that can help to minimize pasture contamination with parasite larva. Rotating pastures with other types of livestock (cattle, sheep, goats) can allow time for the parasite larva to die off before you put horses back on it but you have to have many months between rotations. Picking up feces at least every 2-3 days will also greatly reduce the parasite load on your pastures. (Doing this daily will keep the amount of feces you have to shovel at one time down ) Dragging pastures to break up feces during the very hot, dry southern summers will also help lower parasite burden on pastures, but if you do it during moderate weather it will only help to spread the larva around.

Whatever deworming information you read, make sure it's up-to-date. Many articles and recommendations are based upon old information and that can lead to wasting money and providing poor parasite control for your horses.

Here are some questions to help you and your vet determine the risk of re-exposure and re-infection for your horse’s particular situation.
1. How old is your horse?
2. Is she turned out or stalled?
3. If turned out is it a dry lot or pasture? How much acreage?
4. Do you pick up feces out of the turnout every 2-3 days?
5. Are other horses in the pasture too? If so do they get dewormed regularly? What are their ages?
6. Do you have extreme weather---summers over 100 degrees for extended periods or winters below 40 degrees for extended periods?

Cindy D.
Licensed Veterinary Technician
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post #8 of 15 Old 06-20-2010, 11:52 AM
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If you can have reg. fecals done, and the fecals show no need to treat, I would not treat. If you can't have reg. fecals done, I would worm as usual.
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post #9 of 15 Old 06-20-2010, 12:14 PM
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Worming as usual is generally a waste of money and going to increase the speed with which parasites in your herd become resistant to the drugs you are using.

Having fecals done is simple---you can either drop of a sample at your vet's office or even mail them in to a lab like Horsemen's Lab.

Cindy D.
Licensed Veterinary Technician
Ryle is offline  
post #10 of 15 Old 06-20-2010, 01:44 PM Thread Starter
Green Broke
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I think Smart Pak even has a test kit where you send in a sample and they test egg count in theirs...and it was reasonable, and I have seen some others online too. I think my stable announces when a vet has an appointment to come..I seem to remember an email last week saying he was coming and if we needed samples run to leave a fresh sample in a labeled bag with them.
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