Rotational Deworming… What’s the Right Choice?


Can you please discuss “appropriate” rotational deworming?

Due to the influx of deworming questions, we will tackle them in 2- 3 parts over the next few months.



Standing in the feed store, there are dozens of packages of dewormers, and the age old question of, “which one do I use now?” goes through every horse owners mind.  The answer to this question is not always a simple one.  To appropriately deworm your horse through the year, a rotational deworming program is essential. 

            Here in Colorado, we usually recommend quarterly rotational deworming.  Some herds may require more frequent or less frequent deworming, depending on fecal egg counts. (To be discussed here at a later date). 

Rotational deworming is exactly what it sounds like, rotating through different chemical classes of drugs throughout a year’s timeframe.  Though the name brand might be different, the active ingredient is the important part to rotate.  The idea behind rotating the chemical classes is to reduce the chance of a parasite developing resistance to a type of drug (much like antibiotic resistance).

            To begin rotational deworming this fall on an adult horse our recommendation is using an avermectin product.  There are dozens of avermectin products on each shelf, with various name brands (to name a few – Equell, Equimectrin, Ivercare, Rotectin, Zimectrin, and Horse Health Ivermectin and Quest Gel).  Avermectins have a very broad base of activity, but there are a few types of worms that are not killed.

            In the winter quarter, we usually recommend, for an adult horse a benzimidazole product.  When you’re at the counter, the easy way to remember is that you are looking for an active ingredient that ends with “azole.”  A few name brands in this class are Safe-Guard, Panacur, and Anthelcide EQ. 

            In the spring quarter (usually about the time you see us for spring shots), we rotate back to an avermectin product, but usually include praziquantel.  The praziquantel is effective against tapeworms.  The name brands in this class are Equimax, Zimectrin Gold, and Quest Plus.

            To come full circle and cover a full year, in the summer MVS likes to use a pyrantel salt based dewormer.  Some name brands in that class are Strongid Paste, Rotectin P, Pyrantel Pamoate paste and Liqui- Care P.

As another alternative to quarterly deworming, there is the option of daily deworming (feeding a small amount of dewormer every day).  Using one of these products, you still need to “rotate” and 2 times a year give a paste dewormer.  Our recommendations for these horses on daily dewormers are to use an avermectin once a year, and then a benzimidazole about 6 months later. 

            With appropriate rotation of deworming products, your horse should maintain a minimal parasite load. 

            Look for the next post regarding Fecal Egg Counts to round out your deworming knowledge.



In Summary:

MVS Rotational Deworming Recommendations (Quarterly Deworming Schedule):


         Fall:  Avermectin (Ivermectin or Moxidectin)

         Winter:  Benzimidazoles (Fenbendazole or Oxibendazole)

         Sping: Praziquantel w/ Avermectin

         Summer:  Pyrantel Pamoate


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