Not veterinary advice. Worming plans should be set with your vet, who can test your horses and knows which products still work in your area. This article explains the current Australian guidelines in plain language.
If you grew up with horses in Australia, you probably learned to worm every 6 to 8 weeks, rotate the paste, and never miss a dose. That advice is now out of date for adult horses.
In 2025, the Australian Equine Parasitology Advisory Panel published the Australian Guidelines for Equine Internal Parasite Management (AGEIPM) in the Australian Veterinary Journal [1]. They're written for vets, but the message for owners is simple: test first, treat the horses that need it, and worm less often.
Why the old 6–8 week schedule is out
The guidelines describe interval (calendar) worming, "often every 6–8 weeks throughout the life of the horse", and state that it "is no longer recommended for adult horses as frequent and indiscriminate use of anthelmintics is a major driver of resistance" [1].
Resistance is no longer a future problem. The panel reports that resistance in small strongyles and roundworms (Parascaris) is widespread on Australian horse properties, increasing across all three available drug classes: macrocyclic lactones (such as ivermectin and moxidectin), benzimidazoles, and tetrahydropyrimidines (pyrantel) [1]. The RSPCA gives owners the same warning: overuse of worming pastes is leading to resistance, which means the products won't work properly in future [2].
You may still see "every 6–8 weeks" on product labels and some general care pages [3]. Follow the label for dose, but talk to your vet about frequency.
What you're actually targeting
- Adult horses: small strongyles (cyathostomins) are the main target. They were found on 72–100% of surveyed Australian horse properties [1].
- Foals and horses under 12 months: roundworms (Parascaris) are the main concern [1].
- Tapeworm: Australian data suggest low prevalence (under 5%), possibly because so many products include praziquantel or pyrantel [1].
The key test: the faecal egg count (FEC)
A faecal egg count is a simple lab test on a fresh manure sample that counts worm eggs per gram (epg). The guidelines call it "the foundation of practical diagnostics" and note that fewer than 40% of horse managers and vets use it [1].
The guidelines categorise strongyle egg counts like this [1]:
| FEC result | Category |
|---|---|
| Under 200 epg | Low shedder |
| 200–500 epg | Moderate shedder |
| Over 500 epg | High shedder |
These numbers describe how many eggs a horse is spreading on the pasture. They don't measure the total worm burden or how sick the horse is [1].
Here's the surprising part: in a sample of 729 adult Australian Thoroughbreds, 67% were low shedders [1]. Generally a minority (10–30%) of adult horses shed most of the eggs [1]. Worming every horse every 6–8 weeks means treating many horses that don't need it.
What the guidelines suggest for adult horses
The targeted (selective) approach [1]:
- Low shedders get at least one foundation treatment a year, to control tapeworm and bots and reduce the risk of large strongyles (Strongylus vulgaris) getting established. The guidelines suggest a macrocyclic lactone (ML) product, best given in spring or autumn when conditions favour worm transmission.
- Moderate to high shedders get two to four treatments a year.
- Your vet decides whether to use the "moderate" or "high" cut-off depending on risk, such as stocking rate, pasture cover and climate. Larvae do best at 15–25°C [1].
To work out who's a low or high shedder, the guidelines describe using 3–4 well-timed FECs through the year in a stable, closed herd [1].
Leaving some horses untreated also keeps a population of worms on the farm that haven't been exposed to drugs (called refugia), which slows resistance [1].
Young horses are different
The guidelines make an exception for foals, weanlings and yearlings: they may need more treatments than adults, but frequency should still be kept as low as possible [1]. Their summary suggests 3–4 treatments a year may be warranted for young horses, timed for spring and autumn, using an ML-based product with praziquantel in one of them, then moving to FEC-based treatment as the horse matures [1]. Your vet will tailor this.
Does your wormer still work? The FECRT
A faecal egg count reduction test (FECRT) is an egg count before treatment and again afterwards, to see how well the product actually reduced egg output on your property. The guidelines encourage owners to run one on-farm to find out which products are effective [1]. Ask your vet; it's the only way to know whether you're wasting money on a product the worms have beaten.
New arrivals: quarantine and treat
Incoming horses can bring resistant worms. The guidelines recommend [1]:
- keep new horses in a separate quarantine area away from the resident herd
- treat with actives from all three drug classes (your vet will choose the combination)
- ideally do an FEC before and 14 days after treatment
- collect and dispose of manure from the quarantine yard.
The RSPCA similarly suggests yarding new horses after worming and bagging their manure for the tip for at least three days, rather than composting it [2].
Paddock management does a lot of the work
Chemical-free measures matter as much as the paste:
- Pick up manure. The guidelines call timely manure removal "perhaps the most effective way" to interrupt the strongyle lifecycle. In warmer months, aim for 2–3 times a week where possible [1]. The RSPCA suggests daily, or at least every two days, in small paddocks [2].
- Be careful spreading manure. Harrowing and spreading are generally not recommended, except in very hot, dry weather that kills eggs and larvae [1].
- Don't overstock, avoid feeding on the ground where manure is present, and consider cross-grazing with cattle or sheep [2].
Dose by weight, not by guess
Under-dosing helps resistance develop. Agriculture Victoria notes that weight estimation is needed "for determining the correct dosage of worm treatments" [4]. Use a weight tape or our horse weight calculator, and round up to the next dose mark, as your vet advises.
A sample year for an adult horse
This is an illustration of how a plan built on the guidelines might look. Your vet sets the real one.
| When | What |
|---|---|
| Early spring | FEC on every horse |
| Spring | Foundation ML treatment for all, plus extra treatment for moderate/high shedders as advised |
| Summer | FEC; treat high shedders only if advised |
| Autumn | FEC; second treatment for moderate/high shedders |
| Winter | FEC to confirm categories |
| Once a year | FECRT to check your products still work |
Record every count, product and date in your horse health record, and set reminders with the care planner.
New Zealand
The 2025 guidelines were developed for Australian conditions, but resistance is an issue in New Zealand too, and the same test-first principles apply. Ask your NZ vet about local guidance.
Frequently asked questions
How do I collect a sample for an egg count? Ask your vet or lab for their instructions and container. Fresh manure is needed, labelled with the horse's name.
Should I still rotate wormers? Talk to your vet. The guidelines discuss drug rotation and combinations, and the best choice depends on which products still work on your property, which an FECRT will show [1].
The bottom line
- Stop calendar worming adult horses every 6–8 weeks.
- Get faecal egg counts done, and treat by result.
- Every adult still gets at least one treatment a year.
- Check that your wormer works with an FECRT.
- Pick up manure.
