Deworming Cheat Sheet

Deworming Cheat Sheet
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Parasite control is an important part of your horse’s health management. Since parasites develop resistance to commonly used deworming drugs, rotation is no longer the recommended strategy. Here’s what you need to know about the new world of deworming.

First, Some Key Pointers:

    • The goal of modern equine deworming is not to kill all parasites within the horse; rather it is to limit their numbers so that the horse remains healthy.


    • Not all horses have the same worm burdens and therefore should not all be dewormed in the same way. Fecal egg counts (FECs) done by your veterinarian will help determine how frequently you should deworm your horse.


  • The old eight-week rotational-dewormer plan is out the window. Most adult horses only need to be dewormed twice yearly, unless they are high egg shedders, which your vet can determine with a fecal exam.

The New Way to Deworm

Once you and your vet have determined it’s time to deworm, here are some tips:

    • Choose a dewormer with your veterinarian’s help. Lots of parasites are resistant to drugs like fenbendazole throughout the U.S., but in certain locations, it’s still effective against ascarids. Ivermectin and moxidectin are generally effective against small strongyles and bots, as well as Habronema, the cause of summer sores.


    • Determine your horse’s weight with a weight tape so you administer the proper dose of dewormer. Many tubes only go to 1,200 pounds, so large warmbloods and draft crosses may need part of a second tube.


    • Make sure your horse actually receives his full dose of dewormer. This means he can’t spit it out and leave half of the tube on the ground. Administering less than the full dose of dewormer only encourages faster development of parasite resistance. (Flushing hay and grass particles out of his mouth with the hose beforehand works well.)


  • Write down what dewormer you gave and when; records are key for proper parasite management.

The American Association of Equine Practitioners has an excellent handout providing further details on the sometimes-confounding subject of deworming horses at

This article originally appeared in the April 2016 issue of Horse Illustrated magazine. Click here to subscribe!


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