These Internal Parasite Control Guidelines were revised by the AAEP in May 2024. You can access the entire guidelines document by clicking the Download Resource button.

Parasite groups discussed in these guidelines include: Cyathostomins (Small Strongyles), Large strongyles, Anoplocephala perfoliata (Tapeworms), Parascaris spp. (Roundworms; Ascarids), Strongyloides westeri (Threadworms), Oxyuris equi (Pinworms), Gasterophilus spp. (Bots), Habronema and Draschia spp. (Stomach Worms), Onchocerca cervicalis (Neck Threadworm).

Key take-home messages from these Internal Parasite Disease Control Guidelines are:

  • Perform fecal egg count reduction tests (FECRT) annually to ensure that you are using effective dewormers in every herd or barn.
  • Recognize that no anthelmintic will eliminate all parasitic stages from a horse.
  • Continue using fecal egg counts (FEC) once or twice a year to stratify horses into low, medium, and high shedders to reduce pasture contamination.
  • Deworm all horses at a baseline rate (once or twice a year) and target selected horses more often based on FEC (strongyle high shedders).
  • Do not use FEC to diagnose disease in horses; there is no correlation between FEC and disease-causing parasite life stages.
  • Discontinue deworming all horses with fixed intervals year-round (e.g., every 2 months), and stop blindly rotating anthelmintic classes.


Resource Type

  • Guideline


  • Parasites

Publish Date

May 31, 2024