11/09/2026
"Why does my horse need worming when other horses in the paddock don’t?"
With spring FEC results starting to go out, this is a question we hear quite often at FECC.
And the answer comes down, in part, to something called the 80:20 rule.
Around 80% of parasite egg contamination on pasture can come from just 20% of horses, these are our higher shedders.
By identifying and treating these high shedding horses when appropriate, rather than automatically worming the whole herd, we can significantly reduce the number of parasite eggs being added to the pasture while avoiding unnecessary treatment of lower-shedding horses.
This leads to the follow up question - “My horse is a high shedder, should I be worried?” Being a high shedder does NOT mean your horse is unhealthy or that you should be able to look at them and see they have worms. It simply means your horse tends to shed more parasite eggs in their manure than other horses. My own horse is a consistent high shedder and I would defy anyone to identify that just by looking at him. He is just talented at shedding parasite eggs.
And that's exactly why we test. Two horses can share the same paddock, have the same management and still return very different FEC results. For our low shedding adult horses, that may mean they don't require treatment this spring and can potentially wait until our late autumn/early winter treatment period.
Keeping in mind individual circumstances matter. Previous treatments, new horses entering the herd, age, reproductive status, health, pasture conditions and weather can all influence our recommendations. Foals, young horses, pregnant mares and some older or unwell horses may also require a different parasite-management approach.
That's why FECC asks you all those questions when you submit a sample! We aren't just looking at a number, we're looking at your horse and their individual risk.
Test before you worm.