equine health

Pasture, Soil & Grasses

Horse Worms and Worming
When to Deworm Horses
Controlling Horse Worms on Pasture
Worm Resistance to Wormers

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Deworming Your Horse

Does My Horse Need Deworming?

Short answer is YES, especially in Spring and late Autumn each and every year. Despite the promotion of Faecal Egg Counts (FEC) to monitor the worm burden, the general advice being that a low result under 200 epg needs no action, this idea is flawed. The flaw being FECS do not show encysted redworm larvae which emerge to occupy the void, when the mature redworms are cleared by wormers. Your horse can have a low result less than 200epg but within three or four weeks be riddled with new mature redworms. FECS alone will not control the redworm population. You will need a sensible worming schedule and good pasture management, to reduce your horse's worm population to less than 200epg, all year round.

Starting point

Whatever time of year or season you decide to deworm your horse, the starting point is a Faecal Egg Count (FEC)test. The results will show the level of worm burden prior to using a wormer. A low result less than 200 eggs per gram (epg) but above zero will signify that deworming is necessary, but not urgent. Over 250 epg but less than 750 epg indicates deworming is needed as soon as possible, the worms are active. Over 750 epg indicates grazing infected with worm larvae and depending on season encysted larvae emerging. High worm burdens point to poor pasture hygiene. It cannot be stressed enough that poo picking, composting and seasonal deworming are essential to control your horse's worm burden, reducing it to less than 200 epg, all year round.

Worming Schedule

Ideally, your deworming schedule should start in Spring. The lengthening daylight hours coupled with warmth and moisture activates worm activity. Eggs that have over wintered on grazing, start to hatch once the temperatures reach double figures, over 10 degrees centigrade. The old rule was 3 weeks after horses go out to grass start deworming. No matter what your horse's FEC result, it is essential to deworm in Spring, followed by a FEC test. This will remove young new season larvae picked up from grazing and encysted larvae emerging from the gut wall. Think of this as an internal parasite Spring clean.

A FEC taken 14 days, after the last dose of wormer is essential to establish the worm burden. Results may not be as expected, a higher result than the FEC test taken prior to worming, confirms the presence of encysted larvae emerging into the gut. Encysted red worm larvae often fill the void when the small intestine is cleared of larvae and adult worms. Much like squatters they note a vacant home and waste no time in occupying. Immediately, redose to clear the unwanted (squatters) encysted larvae maturing into adult worms. Followed by a FEC.

In June, dose again to check the redworm population building up, followed by a FEC. A low egg count less than 200 epg means deworming can be put on hold over the hot summer months of July and August. The September rains, misty mornings with warmth and moisture again encourages worm activity, eggs hatch and larvae survive on grazing.

The Autumn dosing should be followed by a FEC. Results over 750 epg again point to emerging encysted larvae maturing into egg laying adults. Redworm larvae can encyst, hibernate for 2 or 3 years then emerge when conditions suit (Spring & Autumn). The squatters move in, once the wormer clears the resident mature worms. Dose again, to clear the newly arrived squatter redworms. The emergence of large numbers of encysted red worm larvae, shows neglect of a proper approach to deworming in previous years.

Mid to Late November, before temperatures dip under 10 degrees centigrade, do your last worming followed by a FEC test. This will clear any redworm larvae that would otherwise start encysting, to hibernate through winter.

The two most important deworming dates are Spring & late November, even though your horse's FEC results are consistently low, don't miss out on these crucial dates.


A blend of traditional herbs added to the feed to maintain the overall health of coat and gut whilst repelling unwanted internal parasites. Added to the feed over 5 consecutive days. One litre is sufficient for an average sized (500kgs) horse for 2 parasite repel applications 8 to 12 weeks apart. Two litres is enough for one average sized horse, to cover the entire year's parasite repel program, 4 seasonal applications in all.

N.B. Not suitable for pregnant/lactating mares or foals under 6 months old.

Contains: Extracts of traditional vermicide & demulcent herbs. One litre self dispensing bottle

Free Faecal Worm Count Kit & Moon Calendar is included and full directions on using Zilch Verm

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