Worming Programmes for Horses
Parasite control in horses has changed significantly over the past decade. Blanket, routine worming of every horse on a fixed calendar schedule is now considered outdated practice, and has contributed to a serious and growing problem: anthelmintic (wormer) resistance. Modern worming programmes are targeted, based on testing, rather than automatic.
Why the approach has changed
Regularly worming every horse regardless of actual burden accelerates the development of resistant parasite populations.
Resistance to some wormer classes is now widespread in UK horse populations, and there are very few new classes of wormer in development — meaning existing products need to be protected and used carefully.
Most horses actually carry a low worm burden most of the time; a small proportion of horses shed the majority of worm eggs onto pasture — testing helps identify these individuals so treatment can be targeted where it's actually needed.
The main parasites of concern
Small redworm (cyathostomins) — the most significant parasite risk in adult UK horses; encysted larval stages can cause serious disease, particularly in late winter/early spring.
Large redworm — less common than in the past due to modern control, but still a risk if control lapses.
Tapeworm — associated with certain types of colic, including impaction and intussusception.
Roundworms (ascarids) — mainly a concern in foals and young horses.
Pinworm — causes tail rubbing but doesn't pose a significant colic risk.
Bots — fly larvae ingested from eggs laid on the coat; generally low clinical significance but worth considering as part of a full picture.
Our recommended approach
Faecal Worm Egg Counts (FWECs): regular testing (typically every 8–12 weeks in the grazing season) to identify horses with a significant strongyle egg burden, so wormers are only used where actually needed.
Tapeworm testing: saliva or blood testing, since tapeworm eggs aren't reliably detected on a standard FWEC.
Targeted treatment: wormers used only for horses that test positive, or as part of a specific seasonal strategy (for example, a winter treatment for encysted small redworm, which isn't picked up by egg counts).
Pasture management: removing droppings from paddocks regularly (ideally twice weekly) significantly reduces pasture larval burden and reliance on chemical control.
New horses: testing and, where appropriate, quarantine worming for any new arrivals before they join the rest of the group, to avoid introducing resistant parasites or high burdens.
Practical tips
Avoid overstocking pasture, and rotate or rest paddocks where possible.
Pick up droppings regularly rather than relying on harrowing alone, which can spread rather than remove larvae.
Test rather than guess — treating "just in case" is one of the main drivers of resistance.
Foals and youngstock have different risk profiles and typically need a more structured, age-specific programme.
Still have questions?
If you'd like help setting up a testing-based worming programme for your horse or yard, please contact us on 01797 252321.