Encysted Small Strongyles
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The Worms You Can’t See… But Should Know About!
Why a clean worm egg count doesn’t always mean a worm-free horse.
Did you know some of the most dangerous parasites in your horse might not show up in a regular faecal egg count (FEC)?
These invisible invaders are called encysted small strongyles (cyathostomins). They’re the larval stage of a very common worm – and they can hide in your horse’s gut wall for months or even years without laying eggs. That means a worm egg count might say “all clear,” even when a serious parasite load is brewing inside.
Why should you care?
When these encysted larvae suddenly emerge, they can cause a condition called larval cyathostominosis, leading to:
Rapid weight loss
Severe diarrhoea
Colic
Even death in severe cases
They don’t show up in a normal FEC – but here’s the important part:
FECs are still a crucial tool.
When larvae hatch and mature, they begin laying eggs – and that’s when we’ll suddenly see a spike in egg counts.
A sudden jump can be an early warning sign that encysted larvae have emerged, and action might be needed.
Regular FEC testing helps you:
Monitor worm burdens over time
Catch changes before they become a health crisis
Avoid over-worming or under-worming
Make informed choices about when (and if) treatments like moxidectin are necessary
What can you do?
Test with FECs every 8–12 weeks
Watch for weight loss or digestive upset
Use targeted treatments only when needed
Chat with your vet or a parasitology-trained professional (like me!) if you’re unsure
I’m here to help – with fast, affordable FECs and science-backed advice to protect your horse from the inside out.
Based in Tasmania
Qualified medical scientist with parasitology training
Horse lover and owner
DM me or drop off a sample at our local points!
📚 Reference: Based on AAEP and WAAVP parasite control guidelines and equine parasitology research, including cyathostomin lifecycle and larval disease risk.
aaep.org/guidelines/internal-parasite-control-guidelines
Image Source: Diagram courtesy of Westgate Labs. Used to illustrate the lifecycle of small redworms.
https://www.westgatelabs.co.uk
