Horse Worming: It’s Not Just When You Worm, It’s What You Use

It’s a common rule of thumb to worm horses at the change of each season. Autumn rolls around, and it’s time to treat. Then again in winter, spring and summer – simple, routine, and easy to stick to. While that approach is largely correct, it can lead to some parasites being missed and may also increase the risk of resistance over time.

Moving from autumn into winter, things can feel like they’re slowing down. Pasture growth drops off, temperatures cool, and overall activity seems lower.

But parasite pressure doesn’t disappear – it just changes.

Some worms persist on pasture, while others remain inside the horse in different stages of their lifecycle. So even if you’re not seeing obvious signs, there can still be a burden there ticking along in the background.

During autumn, and into winter, the key worms to watch for are small strongyles, tapeworms and, in some cases, roundworms – each behaving slightly differently as conditions cool.

Which worms’ matter through autumn and winter?
Small strongyles are one of the biggest considerations at this time of year. Over the cooler months, they can sit in an encysted (dormant) stage within the gut lining. They’re not always causing obvious issues immediately, but they can build up and emerge later.

Roundworms tend to be more of a concern in younger horses but are still worth keeping in mind depending on your age groups.

Tapeworms are a bit different again. Unlike strongyles and roundworms, horses don’t pick up tapeworms directly from pasture. Instead, they’re infected by ingesting small pasture mites (oribatid mites) that act as an intermediate host. This means their lifecycle is slower and more seasonal, and they tend to build up over time rather than spike quickly.

Because of this, tapeworms are often targeted at specific times of year – with autumn being a common point to address them.

Why product choice matters
To target encysted small strongyles, actives such as moxidectin or specific fenbendazole programs are commonly used.

For tapeworm, actives such as praziquantel or pyrantel (at the correct dose) are typically used, often as part of an autumn treatment.

For roundworms, particularly in younger horses, actives such as fenbendazole or pyrantel may be used depending on the situation.

For broader parasite control, combination actives may be used where multiple parasites are being targeted at once.

During the autumn to winter period, the focus is often on managing existing burdens and targeting parasites that persist through cooler conditions.

This is where products such as iO Fenbender, iO Equiduo Liquid and iO Blade can play a role within a broader worming program, as they contain actives suited to targeting common parasites during this time of year.

Product choice should always be guided by what you’re looking to target, along with faecal egg counts, seasonal conditions and your overall worming approach. If you require further assistance, consult your local veterinarian.

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