Parasite Control in Horses


Horses can become infected with both ectoparasites (lice and mites) and endoparasites (worms). The effect of a parasite infection on the horse's health depends on the number and type of parasite involved. Generally, the higher the parasite burden, the higher the risk of clinical disease.


Clinical signs can vary anything from a dull coat and lethargy, to severe weight-loss, diarrhoea, colic and in more severe circumstances death.

Infections with ectoparasites are often identified through examination of the horses coat. It can be almost impossible to identify those horses with high endoparasite infections just by looking at them. It is therefore important for the horse owner to be able to identify and control endoparasite infections in their horses.


Traditionally horses have been treated with dewormers (anthelmintics) at set intervals throughout the year, however this regime can lead to unnecessary use of anthelmintic drugs in horses. This practice of unnecessary use is contributing to worming resistance, similar to antibiotic resistance in humane medicine, and therefore we encourage our clients to follow a strategic worming plan.


Strategic worming plans target those animals that are contributing to pasture contamination the most, due to having higher egg-producing worm burdens. A common myth is that having a herd of horses free from any worms at all is the aim of worm control. This is untrue and the aim of a strategic plan is to maintain a low level of parasites that are susceptible to wormers or “in refugia”. This prevents having a completely naïve herd and allows for the herd to develop a level of natural immunity to the parasites. The use of anthelmintics (wormers) only plays a part in a strategic worming plan. The most important aspect of controlling equine parasites is pasture management as this is the main source of infection.


Best Practice Guidelines


  1. Remove all droppings from pasture at least twice a week. This helps reduce contamination of the pasture from parasite eggs and larvae that are passed in the horse's droppings

  2. Try to keep stocking density to a minimum

Rotate grazing with non-equines eg sheep and cattle to interrupt the parasite life-cycle

Conduct faecal egg counts (FEC) on all horses and only administer a wormer to those with a count >200epg

Worm all horses at the end of the grazing season (late autumn/winter), irrespective of FEC, with a wormer that targets encysted red worm (currently a wormer containing the drug moxidectin and try to avoid use of this wormer at all other times)

  1. Test for tapeworm (either blood test or saliva test) once a year and worm accordingly

Quarantine all new horses for 72hrs after administering an appropriate anthelmintic before allowing onto grazing


We are able to provide collection kits in order for you to conduct FEC on the horses in your care. We are then able to offer advice as to which horses require treatment and the most suitable wormer to use. Please contact the office for more information.



Some of the most popular worms in horses are as below:


  • Large & Small Redworms (Strongyles/Cyathostomes)


  • Round worm (Ascarids)


  • Pin worm (Oxyuris equi)


  • Tapeworm



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