For a long time many owners dewormed on a fixed calendar — every three or four months, whether the horse needed it or not. Today vets instead recommend targeted (selective) deworming driven by fecal egg counts. This guide explains why, and what it means in practice.
Important: This is a general introduction, not veterinary advice. Which tests to run, which product to use and at what dose are always decided by your veterinarian based on your specific horses and your grazing.
Why routine deworming fell out of favour
Worming every horse on a routine, regardless of need, has driven a growing problem: resistance. Parasites develop tolerance to the dewormers, and because very few new products are being developed, it’s important to use the ones we have sparingly and precisely. So the modern principle is: only treat the horses that genuinely need it, at the right time.
The fecal egg count drives treatment
The foundation of modern deworming is the fecal egg count (analysis of worm eggs in the manure). The test shows which horses carry a high parasite burden and actually need treatment.
| Step | What you do |
|---|---|
| 1. Take a sample | Collect a manure sample per your vet’s instructions, often before turnout and during the season |
| 2. Analysis | The sample is analysed for worm eggs (EPG — eggs per gram) |
| 3. Treat as needed | Horses with high egg counts are treated; low shedders are often left untreated |
| 4. Follow up | A check sample can confirm the product worked |
This way the right horse is treated at the right time, instead of everyone getting a product unnecessarily.
Prescription-only in many countries
One important thing to know: in several countries — including Sweden — equine dewormers are prescription-only. You obtain them through a vet or pharmacy after they’re prescribed, not freely off the shelf. That means your vet is involved anyway — take the chance to ask for a plan covering the whole yard at once. (Rules vary by country, so check what applies where you are.)
Season and grazing routines matter
Deworming is tied to grazing. A few general principles:
- Removing droppings from paddocks reduces infection pressure more than any dewormer — parasite eggs spread via manure on the pasture.
- Rotating grazing (not keeping the same horses on the same ground year after year) helps break the parasites’ life cycle.
- Youngsters and older horses may need closer follow-up than healthy adults.
- New horses should have a fecal egg count before being turned out with the rest of the yard.
Common mistakes to avoid
- Worming “just to be safe” without a test — it accelerates resistance.
- Underdosing by guessing the horse’s weight. Weigh it or use a weigh tape.
- Forgetting the poo-picking and assuming the product solves everything.
- Not documenting what was given and when — especially in a yard with many horses.
Keep the treatment history in one place
Just like vaccinations, it’s easy to lose track of which horse got what. In EquiDuty you log each treatment with a date, so you and your vet can always see the history — and so the right horse gets the right follow-up. Read more about how the health journal and full horse registry work in our post on vaccinations and the health diary, where all health information lives.
Modern deworming is about doing less, but doing it right. Take fecal egg counts, follow your vet’s plan, look after the paddocks — and let a digital record keep track of the rest.