Rotating Wormers
Why “Rotating Wormers” is Doing More Harm Than Good
Let’s bust a common myth in horse care…
For years, horse owners were told to rotate between different wormer brands or active ingredients every few months. The idea was that this would “outsmart” the worms and stop resistance from developing.
But we now know:
This outdated practice actually speeds up resistance.
Here’s how:
Rotating without testing exposes worms to multiple drug classes — unnecessarily.
This means more frequent exposure to chemicals, even if your horse doesn’t need treatment. It wipes out the susceptible worms, leaving the resistant ones behind to reproduce.
Over time, that creates a worm population that no wormer can kill — and that’s a serious threat to every horse.
What should you do instead?
Switch to a Targeted Worm Control approach:
Test first with a Faecal Egg Count (FEC) to see if treatment is actually needed.
Only treat when egg counts are high, reducing chemical exposure.
When treatment is needed, choose the right active ingredient based on your horse’s history and resistance risk — not a rotation schedule.
Follow up with a FEC Reduction Test if resistance is suspected.
This strategy:
Protects your horse
Protects wormers from becoming useless
Saves you money in unnecessary treatments
Mal’s Equine Worm Egg Counts makes this easy with quick, affordable testing and clear advice.
FECs are just $15
No guesswork — just smart, science-backed care for your horse.
Message me to get started, or tag a friend who still thinks rotating is the way to go!
Reference: Information adapted from guidelines published by the American Association of Equine Practitioners (AAEP), the World Association for the Advancement of Veterinary Parasitology (WAAVP), and research by Dr. Martin Nielsen and others, which highlight the risks of rotational deworming and support targeted, test-based parasite control programs.
