horse parasite control

The American Association of Equine Practitioners (AAEP) has released an updated version of its parasite control guidelines for horses. The horse parasite control guidelines, first published in 2013, have been revised and to reflect recent research findings.

For the past several years, Martin Nielsen, DVM, PhD, Dipl. ACVM, Schlaikjer Professor of Equine Infectious Disease and associate professor at University of Kentucky (UK) Gluck Equine Research Center, in Lexington, has led the AAEP horse parasite control guideline subcommittee.

A key takeaway from the newly released guidelines: Different equine age groups have different parasite control needs. Fecal egg count surveillance is a necessity, but it should be applied in different manners in foals, yearlings, and adult horses.

In foals, the main target is the large roundworm (Parascaris spp), while small strongyles and tapeworms primarily infect yearlings. Adult horses typically have much lower parasite burdens than those in the younger age groups.

The guidelines identify a basic treatment foundation which should be considered for all horses every year. Fecal egg counts can then identify which parasites the horses are harboring (in foals and short yearlings), which horses are the higher strongyle shedders (adult horses), and whether the treatment worked as intended (all age groups).

Table 1 (below) summarizes the current levels of dewormer resistance in important horse parasites. All equine dewormers have resistance issues in at least one parasite category, and these are global trends. It is important to follow the guidelines and ensure that our horses receive adequate parasite control.

Table 1: Current levels of resistance documented in peer-reviewed studies in major nematode parasites to the three anthelmintic classes in managed horse herds. These are worldwide trends that have also been reported in several U.S. surveys.
Drug Class Cyathostomins Large Strongyles Parascaris spp
Benzimidazoles Widespread None Early indications
Pyrimidines Common None Early indications
Macrocyclic lactones Early indications None Widespread
Widespread: reported on multiple continents with high farm prevalences often above 80%
Common: reported on multiple continents with varying farm prevalences
Early indications: few single-farm cases of reduced efficacy (ascarids) or reports of reduced egg reappearance periods (strongyles)


Read the entire updated guidelines document at

Martin Nielsen, DVM, PhD, Dipl. ACVM, Schlaikjer Professor of Equine Infectious Disease and associate professor at UK Gluck Equine Research Center, provided this information.

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More information on Gluck Equine Research Center and UK Ag Equine Programs.