How To Strategically Deworm Your Horse

Written By: The Irongate Equine Team

Written By: The Irongate Equine Team

There are a few different schools of thought on deworming, and ours is, “less is more”. Instead of deworming your horse with every product available, we focus on what they need to be dewormed with, and how we can get the most bang for our buck.

What are the Goals of Strategic Deworming?

Strategic deworming is a program designed to:

  • Control clinical parasitism and environmental contamination;

  • Determine if parasites on the farm are resistant to any of the deworming products we intend to use; and

  • Prevent the development of parasite resistance (i.e. when dewormers don’t kill parasites) to deworming products in use currently.

  • It is not our goal to eradicate all parasites or to make moderate and high shedders into low shedders. Our goal is to treat clinical problems related to parasites, control environmental contamination, and treat your horse with the deworming protocol appropriate for him/her.

Why Should You Practice Strategic Deworming?

Your horse is an individual, and he should be dewormed that way. Fecal egg counts are performed to determine which dewormers are best for your horse and farm, as well as how often they should be used. We recommend that you perform fecal egg counts biannually until you’ve reached a consistent result for two years or more. Horses do develop a certain level of natural immunity to parasites as they are exposed to parasites over the course of their lifetime. However, this level of immunity may change if the horse’s immune status changes due to pregnancy, stress, performance levels or health issues, such as aging, illness or Cushing’s syndrome.

More does not equal better. Historically, it was common practice to deworm all horses every two months. However, in many horses, deworming every 8 weeks is far more frequent than is required to control that individual’s parasite issues.  This overuse of deworming products has put strong selective pressure on parasites, which has led to localized resistant populations of parasites – not to mention more pressure on your wallet than is necessary. 

How to Practice Strategic Deworming

Deworm the horses that are producing the most eggs. Typically, 20% of the horses are shedding 80% of the eggs into the environment. No stigma should be attached to these high-shedding horses. Their high shedding is merely a function of their innate immunity to parasites and does not suggest poor care. These horses should not be separated from the rest of their herd mates, either. Horses should be grouped by age (two-year-olds and younger should be separated from the rest of the herd) to reduce their exposure to certain parasites and to maximize the deworming program for that group.

Environmental control is also important. Management practices that can be utilized, although not always practical and/or possible, include the following:

  • Pick-up and dispose of manure in pastures regularly – this is the best dewormer of all;

  • Mow/harrow pastures regularly to break up manure piles and expose parasite eggs and larvae to the weather (when temperature is > 85);

  • Leave pastures empty for 4 weeks after mowing/harrowing pastures;

  • Rotate pastures with other livestock to break up life cycles of parasites; and

  • Avoid over-stocking and over-grazing pastures.

The theory of this deworming protocol is to deworm the horses that are producing the most eggs and therefore contaminating your pastures. Moderate and high shedders will be dewormed more frequently than the low shedders to decrease the number of eggs they are leaving in the pasture.

What Dewormers Will I Use?

There are many different dewormers on the market and it can be difficult to keep track of what you need to use on your horse. The goal is to limit the dewormers that the parasites are exposed to in order to slow the development of drug-resistant parasites while controlling the parasites your horse may come into contact with that are clinically significant. Here are the major deworming products we use, and what active ingredient is utilized.


How Do I Get Started?

Here is a great set of instructions you can keep for your records.

  1. Wait an appropriate amount of time after your last deworming.

    1. Wait 8-10 weeks after using Strongid, Panacur, or Anthelcide.

    2. Wait 12 weeks after using any ivermectin product (see above).

    3. Wait 16 weeks after using Quest or Quest Plus.

  2. Collect fecal samples for all of the horses in your herd. If your horse is under 12 months of age, you do not need to perform a fecal egg count – we already know that he’ll be a high shedder. Contact the office to develop a plan.

  3. Collect 1-2 fresh fecal balls per horse. Ideally, you will collect a sample that is free of dirt or bedding, that is from the middle of a pile, and that is less than two hours old. The easiest way to do this is to stall your horse for a few hours and collect from a fresh pile.

  4. Place the sample is a ziplock bag and express as much air from the bag as possible.

  5. Label the bag with the owner’s first and last name, the horse’s name and age, the date of the collection, the last time you dewormed the horse, and what deworming product you last used on the horse.

  6. The sample should be refrigerated, NOT frozen, until tested.

  7. Ensure that the sample is with the office or veterinarians within 5 days of collection. You can bring the sample to the office (we’re open from 8am – 5pm, Monday – Friday) or give the sample to your veterinarian while they’re at your farm.

  8. After testing, the office will contact you with each horse’s shedding class, and instructions for deworming.

    1. Low Shedder – Fewer than 200 eggs per gram of fecal matter.

    2. Moderate Shedder – Between 200 and 500 eggs per gram of fecal matter.

    3. High Shedder – More than 500 eggs per gram of fecal matter.

Please contact us with any questions or concerns that you may have.