Most adult horses are dewormed twice a year, once in spring after the last frost and once in fall before the first frost. But the smarter modern approach is to ask your vet for a fecal egg count first. That test shows whether your horse is a low or high shedder so you can target the right dewormer instead of blanket-treating.
Foals and young horses under three shed far more and need a more frequent, specialized schedule, and any new arrival should be quarantined and tested before it joins the herd.
With a herd my size and foals hitting the ground every season, deworming isn't something I eyeball. I lean on my vet, fecal testing, and a targeted plan rather than dumping the same tube in every horse.
Key Takeaways
- Deworm most healthy adult horses twice a year, in spring and fall, adjusting up only for confirmed high shedders.
- Start with a fecal egg count (FEC) so you treat based on what a horse actually sheds, not the calendar alone.
- Fall deworming targets encysted small strongyles and tapeworms, but it isn't an automatic rule for every horse.
- Foals need a specialized schedule, at least four dewormings in their first year, starting around 2 to 3 months old.
- Always quarantine and test new arrivals before turning them out with the herd.
Why Deworming Advice Has Changed
Knowing when to worm horses used to be simple: rotate a dewormer every couple of months and call it done. We now know that old habit created drug-resistant parasites, and the tubes in the tack room don't work as well as they used to.
The modern approach is more targeted and, honestly, easier on both your horse and your wallet. If deworming and other care words are still new to you, my beginner's guide to horse terms is a helpful companion.
For decades, owners dewormed every horse on the same rotating calendar whether the horse needed it or not. Parasites adapted, and today resistance to some dewormers is widespread. There are no brand-new classes of horse dewormer coming to rescue us, so protecting the ones we have is the whole game.
That's why vets moved to a strategic, evidence-based model built around fecal egg counts rather than the calendar alone. You treat based on what a horse actually sheds, not a one-size-fits-all rule. It's the same kind of shift toward smarter, science-backed care I try to bring to everything on the farm, right down to fun horse facts most people don't know.
Start With a Fecal Egg Count
A fecal egg count is a simple lab test on a manure sample that measures how many parasite eggs a horse is shedding. It sorts horses into rough groups:
- Low shedders: the majority of adult horses. They carry few parasites and need minimal deworming.
- Moderate shedders: a middle group treated a bit more often.
- High shedders: a smaller number of horses responsible for most of the pasture contamination. They need targeted, more frequent treatment.
Running an FEC before you treat tells you which horses actually need a dewormer and lets you choose the right product. Your local vet can run the test and read it in the context of your region and pasture.
A Modern Equine Deworming Program
A practical, resistance-conscious program for healthy adult horses looks like this:
| Timing | What it targets | Common active ingredients |
|---|---|---|
| Spring (after last frost) | Small strongyles, large strongyles | Ivermectin or moxidectin |
| Fall (before first frost) | Encysted small strongyles, tapeworms, bots | Moxidectin and/or praziquantel |
| Extra treatments | Only for confirmed high shedders | Based on FEC results and vet advice |
Two well-timed treatments a year cover most adult horses. High shedders get more, low shedders often get less. This targeted deworming keeps the products effective for the horses that truly need them.
Should You Deworm Horses in the Fall?
Fall deworming is valuable, but it isn't an automatic rule for every horse. The fall treatment is really about two specific targets: encysted small strongyles that hunker down in the gut wall over winter, and tapeworms.
A dewormer with moxidectin for the encysted stage plus praziquantel for tapeworms is the classic fall combination.
The nuance: whether an individual horse needs it, and exactly what product, should still tie back to your FEC results, your climate, and your vet's read on your area. In warm regions the parasite calendar differs from cold ones. So treat fall deworming as a strong recommendation to plan around, not a universal law you apply blindly to every horse on the property.
Foals, Yearlings, and New Arrivals
Young horses are the big exception to the "twice a year" idea.
- Foals: under three years old they shed far more eggs and are vulnerable to roundworms (ascarids). Foals typically need deworming at least four times in their first year, starting around 2 to 3 months of age.
- Yearlings and young horses: stay on a more frequent, vet-guided schedule until they mature into the adult program. This overlaps with other big milestones like weaning.
- New arrivals: always quarantine a new horse, run a fecal egg count, and treat before turning it out with the herd. This is how you keep resistant parasites off your property.
How We Handle Deworming at Running Springs
With foals arriving during breeding season, deworming here is a planned, vet-guided system, not a guessing game. The young ones get the closer schedule they need while they're growing, and any horse coming onto the farm goes through quarantine and testing first.
It's less product overall and better protection, which is exactly the trade you want. You can meet the horses I'm protecting in Meet the Herd, and see the wider menagerie in the animal kingdom at Running Springs.
Barn health days mean a lot of time on my feet. My Katie's Classics line is what I wear for every round of chores.
Final Thoughts on When to Worm Horses
The best deworming schedule isn't a rigid calendar, it's a plan built with your vet around fecal egg counts, your horse's age, and your region. Treat the horses that need it, when they need it, and you protect both your herd and the dewormers we can't afford to lose.
This article is general information, not veterinary advice. Always build your deworming plan with your own veterinarian.
Frequently Asked Questions
How often should you deworm an adult horse?
Most healthy adult horses need deworming twice a year, in spring and fall, adjusted up for confirmed high shedders based on a fecal egg count.
What is a fecal egg count and why does it matter?
It's a lab test on a manure sample that measures parasite eggs shed. It tells you whether a horse needs treatment and which product to use, so you avoid overusing dewormers.
Can you over-deworm a horse?
Yes. Deworming too often drives drug resistance and doesn't add protection for low shedders. Targeted treatment based on testing is the goal.
When should you deworm a new horse?
Quarantine it on arrival, run a fecal egg count, and deworm before turning it out with your other horses to avoid introducing resistant parasites.
About the Author
Hi, I am Katie Van Slyke!
I breed AQHA Quarter Horses at my family farm in Tennessee, stand two stallions, and document foaling season every year from the barn floor while sharing the daily realities of farm life.
I am incredibly lucky to share this journey with millions of friends across YouTube, TikTok, Facebook, and Instagram. You can read the full story of how it all started on my about page.
Sources
The general deworming guidance in this article is supported by the equine references below. Everything about my own herd comes from firsthand experience at Running Springs.
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