How often you should worm a horse is no longer answered by a fixed schedule - modern parasite control focuses on targeted treatment, testing, and reducing resistance. Routine deworming is being replaced by a smarter, evidence-based approach.

Key Takeaways

  • Routine, blanket worming is outdated and contributed to growing dewormer resistance across UK horse populations.

  • Faecal Egg Counts (FECs) help identify which horses actually need treatment, avoiding unncecessary dosing.

  • Different parasites require different treatments - there is no one-size-fits-all deworming plan.

  • The SMART Worming approach combines testing, risk assessment, and pasture management for sustainable parasite control.

Take the guesswork out of deworming your horse - view the schedule here.

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.

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.

row of horses outside

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 redworm or roundworm 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.

Horse Deworming Schedule

Season

Focus

Key Parasites/Actions

Recommended Treatment Approach

Spring (Mar-May)

Tapeworms

Tapeworm testing (high-risk horses)

Treat positives with praziquantel

Spring-Autumn (Mar-Nov)

Redworms

FEC every 8 weeks (high-risk) or 12 weeks (low-risk)

Treat high counts with pyrantel or ivermectin

Summer (Jun-Aug)

Redworms

Continue monitoring FEC results

Targeted treatment only if required

Autumn (Sep-Nov)

Tapeworms

Tapeworm testing (all horses)

Treat positives with praziquantel

Autumn-Winter (Sep-Feb)

Encysted redworms

Risk-based treatment

High risk consider moxidectin (or fenbendazole)

Winter (Dec-Feb)

Low parasite activity

Strategic control of remaining burdens

Ivermectin may be used if needed

For more information on worming foals and yearlings, and management practices to minimise worm burdens, read the full SMART worming guide.

Smarter Worming Starts Here

Routine deworming is being replaced by a targeted, evidence-based approach that protects your horse and helps prevent resistance. By using faecal egg counts and only treating when needed, you can take control of your horse’s parasite management with confidence.

Explore Viovet’s horse worm testing kits to get started.

horse worming range banner

This article was written by James Carrier BVSc MSc MRCVS. James is a veterinary adviser with Boehringer Ingelheim Animal Health, based in the North of England. His interests include infectious disease, sustainable medicine, and science communication.

An educational service from the makers of Eqvalan® oral paste for horses and Eqvalan Duo® oral paste. Further information available in the SPC or from Boehringer Ingelheim Animal Health UK Ltd, RG12 8YS, UK. ©2026. All rights reserved. Date of preparation: Jun 2026. UI-EQU-0064-2026. Use Medicines Responsibly.

Written by: James Carrier BVSc, MSc MRCVS (Guest Author)