Advice & FAQs

What are the main types of Worms affecting Horses ?

Redworm – very common, cause ill-thrift and disease. These worms migrate through the wall of the gut, the large strongyles entering the circulation and the small strongyles encyst in the gut wall.

Tapeworms – less common, implicated in some forms of colic

Ascarids and threadworms – very important in foals

Lungworms – uncommon, except in donkeys

Pinworms  - lay eggs around rectum causing irritation.

Bots – the adult worms in the stomach rarely cause disease but the worms cause annoyance as they lay their eggs on the skin.

When should I worm my horse?

Horses should be wormed routinely throughout the year for the control of roundworms, with strategic treatments given at specific times for the control of tapeworms, bots and most importantly encysted small redworm.

I understand that encysted small redworms are the biggest threat to my horse – what treatments are available to control this parasitic stage?

Traditionally, the only licensed treatment to control encysted small redworm was a 5-day course of a fenbendazole–based wormer. However, in 2003 a moxidectin-based wormer was granted a licence for the control of all stages of encysted small redworm with a unique single standard dose.

It is important to note that with the fact that there is widespread small redworm resistance to benzimidazole-based wormers (i.e. fenbendazole), use of fenbendazole is not advisable where resistance is present

Furthermore recent research has found that a 5-day course of fenbendazole may cause damage to the horse's gut wall, mirroring the situation caused by the actual mass emergence of encysted larvae. Whereas a single dose of moxidectin was found in the same research not to cause severe damage to the horse's gut wall.

When do I need to worm my horse for tapeworms and do I need to double dose?

Treatment for tapeworm is recommended every 6 months . As exposure to tapeworm is greatest during periods of prolonged grazing, treatment should be undertaken in the autumn following summer turnout, and thereafter 6 months later in the spring. Tapeworm can be controlled by a single dose of a praziquantel-based wormer or by a double dose of a pyrantel-based wormer.

What is the main parasite that can affect my horse?

The most common parasite to affect horses today is the small redworm (small strongyle/cyathostomin), which can cause diarrhoea, rapid and severe weight loss, as well as life-threatening colic.

My horse has a heavy worm burden? How do I start its treatment?

If you are concerned that your horse has a very high worm burden it is advisable to contact your veterinary surgeon to establish a treatment specific to your horse’s needs. One possible strategy would be to use a wormer that controls adult worms only, such as a pyrantel-based wormer. This treatment can then be followed 7-10 days later with a moxidectin-based wormer to treat for the remaining larval parasites. A tapeworm treatment should also be given if necessary.

What is the difference between strategic and routine worming?

A strategic worming programme involves the use of Faecal Worm Egg Counts (FWEC) throughout the year with extended dosing interval periods between treatments. Horses on this programme are treated only when FWEC results are above a specified level i.e. 200 eggs per gram (epg). Care must be taken with this strategy, as FWEC do not give an accurate measure of the worm burden; not accounting for larval stages including encysted small redworm larvae present in the horse. Routine worming is the use of equine anthelmintics throughout the year in accordance with dosing intervals recommended by the manufacturer to treat for roundworms, tapeworms and bots.

Why do Faecal Worm Egg Counts (FWEC) not diagnose tapeworm?

Tapeworms release their eggs sporadically (irregular intervals) and so FWEC could show a false negative i.e. the result would indicate no eggs are present but in reality the horse does have a tapeworm burden. A tapeworm antigen blood test will give some indication of any tapeworm burden.

What happens if I overdose my horse?

Although a slight overdose of an anthelmintic is unlikely to have harmful effects, as with all drugs, it is important to dose accurately and in accordance with the manufacturer’s recommendations or those given by your vet, especially in low bodyweight foals or pony foals

What about underdosing?

Underdosing will not do the horse any harm, but you would in fact be administering a sub therapeutic level of the drug and thereby exposing the worms to the drug but perhaps not at a sufficient dosage to kill them. Worms that survive treatment may pass on their “immunity” to subsequent generations and so causing the potential for resistance to develop to that drug.

How important is it to weigh horses? Can’t I just guess his weight or give him a whole syringe?

Establishing a horse’s weight by guessing and not using a weigh tape or weigh bridge, means you risk giving your horse an insufficient dose of wormer. By not giving your horse enough treatment for its body weight you risk giving a sub-lethal dose of the drug which will not be enough to kill all resident worms. These will not only be left to continue their life cycle and breed in your horse, but are also given the opportunity to build up immunity and resistance by being exposed to, but not killed by the drug. A small overdose however, is unlikely to do your horse any harm.

If my horse will not take the syringe easily, how can I give him the wormer?

in-feed wormers are available. However, if the active ingredient or product that you plan to use is only available in a syringe, then the correct dose of product can be administered and mixed into the horse’s feed. It is very important that you ensure the horse eats all of the feed and therefore gets the full dose of wormer.

If wormer is added to the horse’s feed, dogs and cats must be kept away and the feed container cleaned thoroughly afterwards.

If I don’t use a whole syringe, can I use the remaining wormer next time?

Always refer to the packaging of the product to see how long the product can be used once open. Remember the product must be stored according to the package instructions and not accessible to children, or other animals. Empty syringes must be disposed of safely.

Do I need to rotate wormers each grazing season to combat resistance?

The idea to rotate wormers was actually derived from the sheep industry, a strategy that has not yet been widely shown in practice to make a significant difference in the length of time for resistance to occur. In fact, computer modelling has suggested that either alternative of ‘no drug rotation’ or ‘more frequent drug rotation’ make no difference to the onset of resistance (Barnes E et al, 1995).

There are a number of factors which may be involved in the development of resistance, with it having been suggested that the most important factors in delaying the onset of resistance is the anthelmintic’s initial kill of resident resistant worms, and secondly reducing the frequency of use of anthelmintic (Dobson R et al, 1996). This means that the ideal anthelmintic is a highly potent one to which there is no resistance, and which can be given as infrequently as possible.

With widespread resistance to benzimidazole-based wormers, and reported resistance to pyrantel and ivermectin-based wormers, there may be little room for choice as to what to rotate onto, as such it is recommended that you consult your vet prior to using one of these.

It has also been shown that of the macrocyclic lactones (moxidectin and ivermectin), moxidectin selects more slowly for resistance (Ranjan S et al) and should therefore be your first choice when using a macrocyclic lactone wormer.

An alternative strategy to rotation is to use a highly effective wormer with no resistance in horses, such as a moxidectin-based wormer. By using moxidectin, you can worm your horse as infrequently as possible (13 week dosing interval), while still protecting his health.

In addition, pasture management and faecal worm egg counts (FWEC) can also play a role in delaying the onset of resistance. Removing dung from the pasture removes most sources of re-infection, including resistant worms (Wolstenholme A et al, 2004) and so breaking their lifecycle. It is possible to extend dosing intervals by using FWEC: only treating animals when they are producing eggs above a specific level. It is important to note, however, that FWEC do not give an indication of larval burden as eggs are only produced by adult worms, therefore FWEC will not give an indication of encysted small redworm larvae harbouring inside your horse.

How frequently do I need to pick up the dung from the pasture?

Dung should be removed regularly, at least twice weekly during the grazing season, and once a week between November and March. Although harsh frosts may kill infective larvae on the pasture, with the milder and wetter climate now experienced in the UK, high levels of infective larvae can occur at any time of the year (Love S, 2003). Thus, there is an increased likelihood of grazing animals acquiring parasite burdens throughout the year. Therefore if the autumn and winter remain mild and wet, the twice-weekly removal of dung will be necessary all year round.

Should I worm my pregnant mare?

It is very important to worm pregnant mares, not only for their own health, but also that of the foal when it is born. Always check that the product you want to use is licensed to treat pregnant and lactating mares and try to worm her before foaling and throughout lactation according to manufacturer’s instructions.

What wormers can I use on pregnant mares?

Horse womerPregnantLactating
Equimax TabletsYesYes
EquitapeAsk VetAsk Vet
Eqvalan PasteYesNo
Eqvalan duoAfter 3 Months Of GestationYes
Maximec PastenoYes not permitted for use in lactating mares producing milk for human consumption
Panacur GranulesyesNo
panacur PasteYesNo
Panacur 10% LiquidYesNo
Panacur 5 Day GuardYesNo
Pyratape P PasteYesYes
Strongid p pasteYesYes


Should I worm foals?

Yes foals should start to get wormed from 4 weeks of age + , they need special treatment as they have no resistance to worms. Mares with foals should be treated before to foaling with an appropriate wormer and preferably grazed on pasture that has not been grazed by other horses in the previous 12 months if this is not possible delay turning them out until June.

What horse wormers can I use on foals?

IngredientAge of foalSuitable wormers to use
Pyrantel Embonate 4 weeks Embo tape, Pyratape p, Strongid p
Ivermectin 6-8 weeks Eqvalan, Eraquell, Animec, Noromectin, Maximec, Bimectin
Fenbendazole** 6-8 weeks Panacur 5 day guard, Panacur granules, Panacur paste
Moxidectin 4 months Equest
Praziquantel*** Any age Equitape


From what age should I start worming my foal?

As foals have a low tolerance to worms they can quickly acquire massive worm burdens; therefore worming of foals should start at four to six weeks of age, and repeated every four weeks until 6 months of age. Thereafter worming can continue as per wormers recommended dosing interval. Always check 'the age from use' of any wormer prior to use.

Worming Donkeys

As in the case of treating horses you must be competent to do so before administering animal medicines such as wormers to donkeys. The products selected for use should chosen on the same grounds as you would do so for other equines which means taking in all the factors involved and developing a worming strategy suitable to the environment and pertaining circumstances. the range of licensed products for donkeys is more limited than for the horse there is still a range which will enable you to plan over a longer period with out over reliance on any one chemical group whilst remembering that there are products in the above list that have different brand names but are in fact the same active ingredients and certain products will treat for a broader spectrum of parasites when used at higher doses. Here at our online store  we are on hand to help in fine tuning or organising any such plan.

There is a limited range of worming products available for worming donkeys on the UK market.

Here is a list of those prducts currently licensed for donkey treatment and available from our online store

Brand NamePackage Declaration
Panacur Equine Horses and other Equines
Panacur Equine GranulesDonkeys and Horses
Panacur Equine PasteHorses and Other Equines
Telmin PasteDonkeys and Horses
Ivermectin pasteDonkeys and Horses
Strongid P PasteDonkeys and Horses
Pyratape PHorses and Other Equines


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