Worming Horses – How often should you worm your horse?

Pasture Management advice for horses:

  • Keep horses with the same grazing companions for herd stability. Rest and rotate grazing and don’t overcrowd fields.
  • Poo-pick as much as possible, at least twice a week to keep parasite levels down. Cross graze pasture with other species if possible eg. Sheep and cattle.
  • Keep new horses separate until tested and treated accordingly.
  • Don’t worm and move; after worming ensure horses stay on the same pasture for a few days to help slow down resistance.
  • When first starting on a targeted worm control programme all horses should be tested when worming is due or slightly overdue to get a true result.
  • Check for resistant worms; if a positive result is found, treat the horse then sample again in about 10-14 days. If the wormer has been effective the second count should be either ‘no eggs seen’ or very low.

 When to test your horse for worms

There are two tests that should form the basis of an effective targeted worm control programme – worm egg counts for redworm and roundworm and the EquiSal saliva test for tapeworm. Both tests give statistical results for the levels of parasites present that can be used to determine whether the horse needs treatment or not.

You may also need to consider bots, pinworm, lungworm and liver fluke in your programme if you suspect a problem. Consult your vet if you have any initial worries about these types of worms.

When should you test?

A mature, healthy horse can follow a very simple pattern of testing and dosing. The basic idea is to test a small dung sample about three times a year to check for the presence of redworm and roundworm and a saliva sample twice a year to test for a tapeworm infection.

A suggested programme

Worming is only required if the tests indicate infection above a certain level. Complete the year by treating for possible encysted redworm in winter. Foals, youngsters, neglected or older horses will require more attention.

Faecal Worm Egg Count (FWEC)

FWECs should be carried out between spring and autumn to give an estimate of how many small redworm (stronglyle-type) eggs an individual horse is shedding in their faeces. Horses that are shedding high numbers may need to be treated to limit the level of infection on pasture. The frequency of testing should be determined with your vet’s guidance and based on your horse and its herd’s risk

Faecal Worm Egg Count Reduction Testing (FWECRT)

Following the results of the FWEC, or if advised by your vet, when you give your horse a dewormer we recommend checking that the treatment has worked.  This simple check gives reassurance that the dewormer did its job, killed the adult worms, and has significantly reduced egg numbers in your horse’s faeces.  Because of its importance in detecting dewormer resistance, many labs offer this reduction test free of charge.  Talk to your vet about performing FWECRT at least once per year to check that the different dewormer drugs are still working on your property.

Tapeworm antibody tests

These tests measure the antibodies to the tapeworm present in your horse’s saliva or blood. Tapeworm eggs are not shed evenly in faeces which makes faecal testing for tapeworm eggs unreliable. An alternative means of assessing whether horses have been exposed to tapeworms is to measure antibody levels in saliva or blood. Testing kits are available through designated manufacturers, or a blood sample can be taken by your vet.

The frequency of tapeworm antibody testing should be determined with your vet’s guidance and based on your horse and its herd’s risk (see risk indicator table below). Testing should ideally be carried out on all horses in the herd at the same time. The likelihood of infection is generally highest in autumn, if you plan to test annually this is the best time.

 Small redworm (Cyathostomin) blood test

There is a commercial blood test that measures antibody levels for small redworm. This aims to give an idea of exposure to small redworms in the preceding few months but at this time we don’t know for sure how long antibody levels are raised after infection has been cleared. The usefulness of this test to monitor small redworm burdens in horses or predict the risk of disease has not been established or validated fully in naturally infected horses at this time.

Tests for Pinworm

If pinworm is suspected, a sticky tape test can be used to detect any eggs that have been laid around the horse’s anus (dock area). The sticky tape lifts cell debris and potentially pinworm eggs. The tape is examined under a microscope to look for the presence of pinworm eggs.

Assessing the need for testing and appropriate treatment

The timing and frequency of testing and possible treatment should be determined on a case-by-case basis, depending on your horse’s and the herd’s risk of worm infection. The table below provides information on a variety of factors which will influence the testing schedule or possible treatment for your situation and management. You should discuss these points with your vet when developing a plan for your horse or yard.


1) Rendle, D et al. (2019). Equine de-worming: a consensus on current best practice. UK Vet Equine.