Parasites affecting horses An overview

With a few exceptions worms are species specific which means that they can only survive and their lifecycle complete in certain animals. Redworm, roundworm & tapeworm are the biggest pathological threats to horses and the parasites for which we should test regularly. We may also need to consider pinworm, bots, lungworm and liverfluke in a parasite control programme.

Each group of parasites has specific characteristics, drugs effective to treat them and some have seasonal threats to be aware of; learn more about each of these and how to manage them here.

Endo - Internal Parasites of horses

Ecto - External Parasites of horses

‘Think twice before using wormers’*

*BVA guidelines on worm control for grazing animals

All the experts now agree that good worm control starts with using worm counts and tests, only adding wormer doses as they are needed. 

Resistance to wormers

Horse worms are evolving to become resistant to some worming drugs, especially those which have been around for a long time. This means that we can no longer rely on keeping horses worm free purely by giving them wormers. It’s much better to know what is going on and target the wormers at the wormy horses and at specific seasonal problems like encysted redworms, bots and pinworm. Using wormers sparingly should also mean that they stay effective for those times when our horses really need them.

Using worm counts and tests

Whether you have a single horse kept on an individual turnout or run a busy yard with mixed turnout a targeted approach can work for you.

How does a worm test programme work? 

A mature, healthy horse can follow a very simple pattern of testing and dosing. A dung sample is taken approximately three times a year to check for the presence of redworm and roundworm and a saliva sample twice a year to test for tapeworm. If all is well then no need to worm. Complete the year by treating for possible encysted redworm in winter.

Foals, youngsters, neglected or older horses will require more attention.

A word about encysted redworm

Encysted stages of redworm are not mature so don’t lay the eggs which are counted in the dung sample. It is important to treat with an effective product in the winter months then rely on worm count results over the next season.