Strategic Deworming

Strategic Deworming

These recommendations were updated October 2018 and are relevant to horses in Wisconsin. These recommendations are for horses 3 years old and older. They are not appropriate for pregnant mares and horse under the age of 3 years old.

Strategic deworming (SD) allows us to minimize the risk of parasitic disease in individual horses while minimizing the amount of chemical deworming medication the horse is exposed to. It also controls parasite shedding into the horse’s environment and minimizes the risk of the parasites developing resistance to the deworming medications. SD involves using fecal exams to evaluate the parasite load of each horse. Each horse is dewormed based on his or her results. Based on SD, most of our horses will be dewormed only 1-2 times per year! The remaining horses will be dewormed either 2-3X per year.

How to collect a fecal sample for examination (FEC):

  1. Label a clean zip-lock baggie with the horse’s name and date of sample collection.
  2. Place 1-2 fecal balls in the baggie. Sample should be less than 12 hours old.
  3. Remove as much air from the baggie as possible and zip it shut. This creates an anaerobic environment that prevents the eggs from hatching and developing in the sample.
  4. Refrigerate the sample until it is turned in for evaluation.


  • March or April or May- Check FEC on every horse.
  • Horses with FEC result of 0-200 eggs per gram (epg) do not get dewormed.
  • Horses with FEC >200 get dewormed.
  • Horses with FEC >500 get a FEC again 12-16 weeks after deworming.


  • Horses with spring FEC >500 need a FEC 12-16 weeks after spring deworming.
  • Of those horses any with a FEC >200 get dewormed.


  • September or October or November-Check FEC on every horse
  • All horses are dewormed. Even horses with 0 epg need to be dewormed for migrating strongyles, bots, tapeworms and pinworms that are not detectable by fecal exam. Not all dewormers kill migrating strongyles and tapeworms.


  • Horses with fall FEC >500 needs a FEC 12-16 weeks after fall deworming.
  • Of those horses any with a FEC >200 get dewormed.

To summarize the above: All horses get a fecal check spring and fall.  Summer and winter fecals need to be done on horses that had a FEC over 500 epg in the previous season. Dr. Weidenkopf will make individualized recommendations on which product to use and when to give it.

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