Worming Schedule? - See post #8

Discussion in 'Horse Health' started by Acantha, Mar 21, 2009.

  1. Acantha

    Acantha Senior Member

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    I live in Northern California, right on the coast. The weather is very mild.
    I was wondering what wormer rotation is best? Is there a rotation that's better than the others?

    On December 15 I gave her Ivermectin, and today I gave her Fenbendazole. (yes, rather overdue, I know. D8) Does it matter what I give her next?
     
    Last edited by a moderator: Mar 22, 2009
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  2. JBandRio

    JBandRio Senior Member

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    Try a search here :) Quite a few threads on this very topic, with very good information :)
     
  3. crayon

    crayon Senior Member

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    I give my horse a different wormer every time I de-worm her. I rotate between Zimecterin Gold, Strogid, and SafeGaurd. They each have different chemicals so there are no immune wormies in there. :)
     
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  4. Acantha

    Acantha Senior Member

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    I'm asking because I've seen people say the rotation you should use depends on your location.
     
  5. crayon

    crayon Senior Member

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    hmmm. I don't know about that... I'm no expert on worming. But I just know that you need to rotate so that the worms don't become immune.
     
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  6. JBandRio

    JBandRio Senior Member

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    There is a fairly high resistance of parasites to both pyrantal pamoate (strongid paste) and fenbendazole (safeguard). So yeah, there ARE immune wormies ;)
     
  7. JBandRio

    JBandRio Senior Member

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    That is absolutely correct.

    Your particular horse might not have a fenbendazole- or pyrantel pamoate-resistant colony of worms. Or he might. The only way to find out is to know you have a parasite issue to begin with (fecal testing), deworm with one of those products, and do another fecal to see how much, if any, decrease in egg count there was.

    If your horse has a high resistance load to either of those, they are not a valid part of that horse's rotation.
     
  8. Ryle

    Ryle Senior Member

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    Actually, there is very high resistance to fenbendazole among strongyles and moderate resistance to pyrantel. Fenbendazole for adult horses is most likely a waste of money....in foals it's still useful for ascarids.

    Here is a repeat of my long-winded deworming post.


    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. 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 soon.

    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
    praziquantel

    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

    As for appropriate dosing intervals, you want to treat according to the egg reappearance period so that you are dosing to prevent continual recontamination of your pastures. This method means that you will be cutting back on your horse's risk of parasite infestation significantly after a year appropriate dewormings because you will have cut the number of parasite larva on your pastures. It also means that you won't be deworming at a time when there are no parasites in the system that will be susceptible to the product you are using next which happens if you dose too soon after ivermectin or moxidectin with pyrantel or fenbendazole because at normal doses these two chemicals only kill adults in the GI tract and if you've dewormed with moxidectin last 8 weeks ago there aren't adults there to kill and you've missed the migrating larva which will then start shedding eggs 4 weeks after you treat with either of these drugs and shed for the 4 weeks until you deworm again. Or if you dewormed with ivermectin 6 weeks ago and treat with either pyrantel or fenbendazole you will start seeing egg shedding into your pasture in 2 weeks because you didn't have adults in the GI tract when you dewormed last but they will be there in a couple of weeks. Or in the case where you actually do have adults for the pyrantel or fenbendazole (which again is not likely to be working) to affect because it's been 8 weeks since your last dose of ivermectin you will again have parasite ova being shed in 4 weeks because that is how long after the use of either of those drugs you start seeing adult egg shedding parasites in the GI tract. So deworming based upon Egg Reappearance Periods, you would deworm and then deworm again based upon what drug you used last--4 weeks later for pyrantel (or Fenbendazole, though the next day would probably be more useful LOL), 8 weeks after ivermectin or 12 weeks after moxidectin. In this manner, you can significantly reduce the parasite load on your pastures in a year's time.

    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?


    http://www.thehorse.com/Parasites/Parasites1204.pdf
    http://www.thehorse.com/ViewArticle.aspx?ID=7317#parasites

     
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  9. Ryle

    Ryle Senior Member

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    The newest recommendations as of June 2009:

    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 www.thehorse.com. 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.

    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.) http://www.thehorse.com/Video.aspx?vID=1…
    (Craig R. Reinemeyer, DVM PhD --parasitologist)
     
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  10. erusaertelttil

    erusaertelttil Full Member

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    GET A WORM COUNT FROM THE VET!
    its the only way to know for sure that your doing the right thing because every horse is different.
     

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