Annual horse worming programme for effective parasite control

Posted by Wormers-direct on 9th Jan 2020

Annual horse worming programme for effective parasite control


View a worming calendar with tactical worming guidelines

View which brands fall in to which chemical group


Nothing is set in stone about what to use and when to use it as you plan your worm control, as opinions vary and of course commercial issues are present too. The entire supply chain of equine wormers is very vigorously regulated, and all those in that supply chain are duty bound to provide the best possible advice and guidance to you, the end user. Here at we have tried to gather all such opinions and research and use that information to provide guidance on your worming planning. Hard evidence shows that continuing use of the same active worming ingredient can lead to resistance, so it seems logical to adopt a rotational approach to product choice.


We have all noticed a climate change in the UK in the last few years with wet summers and warm winters; just the weather parasites love to breed and multiply in. As a result of this, it is even more important to take expert advice when choosing your wormers, as the traditional natural enemy of those pesky parasites are red hot dry summers and very cold winters.

If you have selected to rotate your worming products, make sure you are choosing a different ingredient not just a different brand. Develop an effective worming programme on an annual basis using tactical worming for specific parasites, using faecal worm egg counts and tapeworm tests when conditions are suitable, and rotating active ingredients during the grazing season (not each time you worm your horse). Select one of the distinct chemical groups, which are:

MACROCYCLIC LACTONES lvermectin and Moxidectin
BENZIMIDAZOLES Fenbendazole, Mebendazole, Oxibendazole

Products based solely on Praziquantel only are effective for tapeworm control and must be used in conjunction with products based on the three main chemical groups.

Combination wormers are also available containing lvermectin and Praziquantel. Some containing a combination of Moxidectin and Praziquantel are also available. These products offer great convenience at times when tapeworm treatment is required along with routine worming.

If there are reasons for routine worming on a continual basis, use your selected group during a 12-18 month period with particular emphasis to rotation during the grazing season. The grazing season is basically the summer months and although your selection of products may well be based on an annual selection, it is the grazing season when particular attention should be paid to rotation of the active ingredients. Outside of this season are the occasions when specific worming products should be used for tactical equine worming. Change your selected group annually to a different chemical group so that your stock does not build up a resistance to wormers. Also you must consider the use of faecal worm egg counts and tapeworm tests to help with deciding when, if, and what to treat with.

There has been evidence of a resistance building to products in the Benzimidazole group in certain areas so it is best to take expert advice before relying on products within that group to control worm burden.

- View which brands fall in to which chemical group?


Although most of the leading brands of horse wormers are effective against adult redworms, (take expert advice before relying on Benzimidazoles and ascertain that your horse is infected with worms that are susceptible to it by taking a dung sample and having an egg count done) there are times when you will need to worm tactically to treat for specific worm types. Whichever chemical group you choose to use on an annual basis, you will still need to dose tactically to control encysted small redworm, tapeworm and bots.

- View a worming calendar with tactical worming guidelines


Herbal worming products are now available using a specific combination of plants to repel parasites. As data is limited in regard to how effective these herbal preparations are in combating worm burden, it is best to take expert advice before relying on herbal products.


Different chemicals work in different ways within the body of the dosed horse, so extra thought needs to be given to such circumstances of age, general health condition, administration to mares, foals and stallions and also pasture management. There are many ways in which pasture management such as poo picking, faecal worm egg counts, tapeworm tests and field use can help in reducing the use of chemical wormers. Why not tell the experts about your particular circumstances and let them tailor a plan specifically for you?

A critical time for parasite control is the early months of a horses life, so take special care when treating foals and ensure you select an ingredient that is suitable for use on them, then use that at the correct times.

A common mistake when treating horses is under dosing, so ascertain the weight of your horse as accurately as you can either by using a weight tape or even better a weigh bridge if possible. Correct dosing is important, if you under dose your horse the product will not work efficiently and could lead to the parasites building resistance to the treatment.

If you administer a sub therapeutic level of the drug and thereby expose the worms to the drug, but not at a sufficient dosage to kill them, worms that survive treatment may pass on their “immunity” to subsequent generations. Those generations will become more adept at surviving chemical treatments, with the potential for resistance to develop to that particular drug.

There are now brands on the market that treat up to 700kg bodyweight in a single syringe, giving a little bit extra to play with when dosing. Also, Equimax is now available in tablet form with each pack treating up to 800kg bodyweight. When you estimate the weight of your horse remember we all lie about our weight so if in doubt, err on the generous side when estimating. Although a slight overdose of wormer is unlikely to have harmful effects, as with all drugs, it is important to dose accurately and in accordance with the manufacturer’s recommendations.


Don’t forget the environment when selecting your products, particularly the aquatic life in and around your pastures. Make sure that NO product enters the water courses, and protect the flora and fauna from spillage and waste. Above all be careful when you have your dogs about as some products are very dangerous and can be fatal if ingested by dogs, particularly collies. You must read the instructions on the packaging and keep yourself up to date with the latest thinking.

The above guidelines to an effective worming programme are the opinions of the author and are not the definitive answer. They are however a base for an effective procedure that can be modified with the assistance of your vet or other professionals authorised to advise on animal health. The author hopes that this article will help you to care for your horse but cannot be held responsible for any errors, omissions or changes in acceptable procedure.

We are more than happy to help out with any queries that you may have with regard to worming your horses, please feel free to contact us by email or telephone.