De-Mystifying De-Worming

Deworming Horses

So you’ve been told to de-worm every 6-8 weeks, and to rotate de-wormers. But when you get to the feed store, you’re attacked by thousands of shiny boxes and packets and daily de-wormers, pastes, powders, injectable, etc. So which is right for your horses and your situation?

To begin, it is important to understand a few things:

  1. All horses have some level of infestation – you are not killing all the parasites, just controlling the amount.
  2. There are several classes of parasites that you want to attack, ie. Ascarids, adult strongyles, larval strongyles, bots and tape.
  3. Parasites recycle: an infected horse will shed parasites in its manure. These parasites spread to the grass that is then eaten again by the horse, completing the cycle.

There are pros and cons to each type of de-wormer: pastes are a convenient, one-time dose that now comes in flavors in an attempt to make the application easier. Unfortunately, some horses get smart to it, will hold it in their mouths and when you’re not looking spit the neon green paste all over your black dog. The powder is a daily de-wormer that is spread over feed. If your horse is violently opposed to paste, this is a perfect compromise, and the idea behind it is that it administers a smaller dose on a daily basis to keep the horse’s stomach happy and keep the level of infestation low. Injectables should only be administered by a vet or someone very experienced with giving injections. This is a viable option if your horse would rather kill you than let you shove something in his mouth and will not eat his feed if a powder is added. Unfortunately, horses are smart, and most won’t let you stick them on a regular basis.

How often you de-worm is based on where in the country you are located. Climates that have wet, warm summers are more likely to have a higher infestation, but cold winters and hot, dry climates will keep the parasite population at bay. Also, the more horses/acre there are, the most likely they will be eating grass in or around manure, and the more likely they are to consume parasites. Ask your veterinarian and other local horsemen how often they de-worm.

Different classes of de-wormer attack different types of parasites. Below is a table borrowed from Univ. of Minnesota that explains which class of de-wormer kills which class of parasite. You want to rotate classes of de-wormers to target a different type of parasite each time and to prevent any one type from becoming resilient to the drug.

De-Worming Breakdown

De-Worming Breakdown

If you notice a horse having trouble putting on weight or is acting depressed or has a dull coat, you may need to reexamine your de-worming schedule. Fecal samples can be tested for levels and types of infestation by your vet.

I hope this has cleared up the topic of de-wormers. Write in and let us know if you have any de-worming stories, a tricky horse, success with one form of de-wormer or another, etc. We’d love to hear from you!


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