For years, deworming was one of the most routine parts of horse care. Buy a dewormer, stick to a schedule, rotate brands every few months, and repeat across the whole yard. It felt practical and proactive.
But parasite control has moved on.
Today we know far more about how worms behave, how resistance develops, and how our deworming habits directly affect the long-term health of our horses. This has led to a shift away from blanket, routine deworming, and towards a more targeted, evidence-based approach.
Why did deworming need to change?
Dewormer resistance is no longer a theoretical concern. It is real, increasingly widespread, and affecting horses across the UK. Parasites are adapting to the products we have relied on for decades.
Although there may seem to be a wide range of dewormers available, they are all based on just five main classes of active ingredients, and for now there are no new ones waiting to replace them.
Once resistance develops, our options become increasingly limited.
The five main active ingredients used to treat worms in horses include:
- Fenbendazole, ivermectin, moxidectin and pyrantel, which target worms such as redworms, roundworms and pinworms.
- Praziquantel, which is effective against tapeworms and is only available in combination with ivermectin or moxidectin.
- Pyrantel can also treat tapeworms when given at a double dose.
Protecting the effectiveness of these products is essential.
Which worms matter the most?
Not all worms pose the same level of threat, and not every horse faces the same risks. In adult horses the primary parasites of concern are:
- Small and large redworms
- Roundworms (mainly in foals and youngsters)
- Tapeworms
This is why evidence-based deworming, guided by testing is now widely recommended.
Faecal Egg Counts (FECs) are a key part of this approach. They show which horses are actively shedding eggs and which aren’t.
One size doesn’t fit all
Different worms respond to different products, and resistance patterns vary between species. This means that choosing the right dewormer matters just as much as choosing whether to deworm at all.
The SMART Worming Principle
Sustainable parasite control isn’t about doing nothing; it is about making informed choices. The SMART Worming principle combines:
- Regular risk assessments
- Evidence-led testing such as faecal egg counting (FECs)
- Advice on the appropriate, targeted treatment
- Advice on good pasture management
Factors such as age, grazing habits, stocking density, exposure to new horses, and previous test results all influence a horse’s parasite risk.
The SMART Worming schedule provides a clear, practical framework for assessing risk and planning treatments throughout the year. You can find it here:
An educational service (from the makers of Eqvalan® oral paste for horses and Eqvalan Duo® oral paste (UK only)). Further information available in the SPC or from Boehringer Ingelheim Animal Health UK Ltd, RG12 8YS, UK. ©2026. All rights reserved. Date of preparation: Apr 2026. UI-EQU-0064-2026. Use Medicines Responsibly.