Worming used to be simple: you dosed your pony every six weeks with a tube of paste and that was that. We now know that approach — routine, calendar-driven worming of every horse regardless of need — has created a serious problem: worms are becoming resistant to the drugs we have. The modern approach is smarter, cheaper and better for your pony: test first, treat only when needed, and manage the pasture to reduce infection in the first place. Here is a clear, practical guide for pony owners.
Why the old approach no longer works
For decades, the standard advice was to worm every horse every 6–8 weeks, rotating between different chemical classes. This killed most worms — but the few that survived passed on their resistance to the next generation. After decades of this, some worm species are now resistant to one or more drug classes, and there are no new equine wormers being developed. If we lose the drugs we have, worm-related disease will become far more common and far harder to treat.
The solution is targeted worming: using worm egg counts to identify which ponies actually need treatment, and only treating those. This slows resistance, saves money, and is better for your pony's health.
The parasites that matter
Small redworm (cyathostomins)
The most common and significant parasite in UK ponies. Adult worms live in the large intestine and lay eggs that are passed in droppings. Larvae can encyst (burrow into the gut wall and go dormant) — sometimes in huge numbers — and emerge en masse in late winter or early spring, causing a dangerous condition called larval cyathostominosis, which can be fatal. Encysted larvae do not show up on standard worm egg counts.
Tapeworm
Tapeworms cluster at the junction of the small and large intestine and can cause colic, particularly spasmodic colic. They do not reliably show up on faecal egg counts — a saliva test or blood test is used instead.
Large redworm (strongylus vulgaris)
Once the most dangerous parasite, now rare in the UK thanks to effective worming over decades. Larvae migrate through the blood vessels supplying the gut, causing potentially fatal thromboembolic colic. It is worth knowing about but is uncommon in well-managed ponies.
Roundworms (ascarids)
Mainly a problem in foals and young ponies under 4 years. Adult ponies develop immunity. Large burdens can cause poor growth, coughing (larvae migrate through the lungs) and colic.
Pinworm
Less harmful but very irritating — female pinworms lay eggs around the anus, causing intense itching and tail-rubbing. Not a health emergency but a nuisance and a sign to review your worming programme.
Bots
Bot flies lay eggs on the pony's coat (usually legs or shoulders) in late summer. The larvae are ingested and live in the stomach over winter. Not usually harmful in small numbers but treated as part of a winter worming plan.
Worm egg counts: the foundation of targeted worming
A worm egg count (faecal egg count, or FEC) is a simple, inexpensive test. You collect a fresh sample of your pony's droppings, put it in the container provided, and post it to a lab. The lab counts the number of worm eggs per gram (epg) of faeces and tells you whether your pony needs worming.
Most adult ponies have a low egg count and do not need treatment. A small number — called "high shedders" — carry most of the worm burden and shed most of the eggs onto the pasture. Identifying and treating these ponies is the single most effective thing you can do to control worms on your yard.
How often to test: typically every 3 months during the grazing season (spring to autumn), with results guiding whether to worm. Costs are modest — often £10–£15 per test, sometimes less through your vet or a subscription service.
A typical year-round worming plan
This is a framework — always discuss your specific situation with your vet:
| When | What to do | Why |
|---|---|---|
| Spring (March–April) | Worm egg count. Treat only if high. | Identifies high shedders after winter |
| Summer (June–July) | Worm egg count. Treat only if high. | Monitors grazing-season burden |
| Late summer (August–September) | Tapeworm saliva test. Treat if positive. | Tapeworm does not show on egg counts |
| Autumn (October–November) | Worm egg count. Treat only if high. | Last check before winter |
| Winter (December–January) | Treat for encysted redworm (all ponies) | Encysted larvae cannot be detected by egg counts |
| Winter (after first frost) | Treat for bots (if present) | Kills bot larvae in the stomach |
The winter treatment for encysted redworm is the one exception to "test first" — because encysted larvae cannot be detected by egg counts, most vets recommend a moxidectin-based wormer for all ponies in late autumn or winter. This is the one drug that effectively kills encysted larvae. Use it carefully and only as directed, as resistance is a concern.
Pasture management: prevention is better than treatment
Wormers are only part of the picture. The most effective worm control comes from managing the pasture so your pony does not pick up larvae in the first place:
- Poo-pick regularly — at least twice a week during the grazing season. This removes eggs and larvae before they spread. It is the single most effective thing you can do.
- Do not overstock fields — too many ponies on too little grass forces them to graze close to droppings, where larvae concentrate.
- Rotate grazing — resting fields for 3+ months breaks the worm lifecycle, though UK winters are not cold enough to kill larvae reliably.
- Cross-graze with other species — sheep or cattle grazing horse pastures breaks the worm cycle because horse worms do not infect sheep and vice versa.
- Harrow fields in hot, dry weather — this breaks up droppings and exposes larvae to sunlight and drying. It is ineffective in wet UK conditions.
- Keep new arrivals isolated — worm egg count any new pony before turning it out with others, and treat if needed.
How to give a wormer
- Weigh your pony first — use a weigh-tape. Underdosing is a major cause of resistance. If in doubt, dose slightly over rather than under.
- Check the syringe is the right one — different wormers target different parasites. Make sure you are using the correct active ingredient for the parasite you are treating.
- Administer carefully — insert the syringe into the corner of the mouth, aim for the back of the tongue, and deposit the paste slowly. Hold the head up briefly so the pony swallows rather than spits it out.
- Do a post-dosing egg count — 10–14 days after worming, a second egg count checks whether the treatment worked (a "reduction test"). If the count has not dropped significantly, resistance may be present — discuss with your vet.
Common mistakes to avoid
- Worming every pony on the same schedule regardless of need — this drives resistance and wastes money.
- Underdosing — guessing the pony's weight rather than using a tape. Always weigh first.
- Rotating wormers unnecessarily — modern advice is to use the most effective drug for the target parasite, not to rotate for its own sake.
- Ignoring pasture management — no worming programme can compensate for a field that is never poo-picked.
- Forgetting tapeworm and encysted redworm — these do not show on standard egg counts and need separate testing or treatment.
Next steps
- Set up a worm egg count routine — your vet or an online service can help. Read our daily routine guide to fit poo-picking into your schedule.
- Understand the costs: see what a first pony really costs, including annual worming.
- Keep your pony's weight under control — overweight ponies are more susceptible to parasite-related illness. Read our good-doer management guide.
Test before you treat, poo-pick twice a week, and work with your vet on a tailored plan. That is the modern, responsible way to keep your pony worm-free — and keep the drugs working for the future.