Why is a de-worming programme important and how do I create one for my horse? 

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Why do I need a de-worming programme? 

Heavy infestations of redworm and roundworm can have serious consequences for some horses, as they can cause severe weight loss, diarrhoea, colic and even death. 

It is important to have a de-worming programme in place for your horse(s) to ensure that they receive treatment to prevent them becoming unwell, whilst avoiding unnecessary worming which increases the risk of resistance. 

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What is a de-worming programme? 

A de-worming program is simply a plan put together with the help of your veterinary surgeon to determine when to test and when/if to treat your horse(s) in order to prevent them from developing symptoms of high worm burdens. This ensures we treat the right horse at the right time and with the right wormer. 

How do I create a de-worming programme for my horse? 

An effective and sustainable plan will vary depending on the specific needs of the horse(s) and the general management practices that are in place.  A plan for a stabled single adult horse, will be radically different to that for a foal. It is also important to include pasture management in your program as this can play a significant part in reducing infection and limiting wormer use1


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The principles of a good de-worming plan

The aim of any worming programme is to prevent horses becoming ill due to worm burdens and to reduce pasture contamination with worm eggs, not to eliminate all worms. 



Regular testing


Assess the test results in combination with the horse’s risk level


Only treat those horses who need worming

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Redworms and Roundworms

Faecal Worm Egg Counts (FWEC) 

This is a simple test to check how many worm eggs a horse is passing. It involves sending a sample of your horse’s droppings to a laboratory where the number of worm eggs will be counted. Only horses with a high FWEC need to be treated. This test is useful for redworms and roundworms (but not for tapeworms).  This should be done every 8-12 weeks. 

Faecal Egg Reduction Test

This test is used to check that the wormer has been effective. A FWEC is carried out before treatment and then 2 weeks after treatment, and the two egg counts are compared. If the egg count has not reduced after treatment, this may indicate the presence of resistance to that wormer. This test should be done every year. 


Tapeworm test

Tapeworms cannot usually be detected with FWEC but there is a simple saliva test to check for tapeworm infection. Alternatively, your vet can take a blood sample. This test should be done in autumn (when tapeworm infections are likely to be highest) and repeated in spring for horses at high risk of infection. 

The risk factors to consider:

Is your horse young?

Some protective immunity is usually acquired with age and exposure to certain worms, so older horses are usually at a lower risk than younger horses. 

Ascarids (roundworms) are generally only a concern in foals and youngstock. 

Encysted redworms are rarely a problem in horses over 6 years of age. 

Are your horses grazed with young horses?

Older horses with higher immunity can still develop high worm burdens if they are grazed with youngstock who are shedding high numbers of worm eggs into the environment. 

Are your horses grazed with lots of other horses?

More horses in the environment means more worm eggs will be shed, which means more larvae on the pasture, which means higher worm burdens. 

Are the fields poo-picked less than twice a week?

Worm eggs in the droppings take a few days to develop into infective larvae. Less poo-picking means more larvae on the pasture which means higher worm burdens. 

Have your horses historically had repeated high faecal egg counts?

Some horses will naturally be high egg shedders that need worming frequently, others are low shedders that can be wormed less frequently.  

The more questions you answer yes to, the higher the risk of your horse developing a significant worm burden. 

Treat Accordingly

Although there are many brands of wormer, there are only 5 active ingredients – fenbendazole, ivermectin, moxidectin, praziquantel and pyrantel – and which to use will depend on which worm(s) need to be treated, previous treatment history of the horse(s), and whether resistance is present on your premises.  

It is also crucial to always worm in accordance with your horse’s weight, as under-dosing can lead to resistance in surviving worms, while over-dosing provides no added benefit. 

Pasture management will help to manage your horse’s worm burden, and reduce the number of worm treatments you need to give1

  • Remove faeces from pasture (‘poo-pick’) at least twice weekly.  
  • Avoid spreading horse manure on pasture grazed by horses.  
  • Avoid overstocking and overgrazing.  
  • Rotate grazing with sheep or cattle and/or rest pastures regularly.  
  • Thoroughly clean stables regularly especially when they contain foals and weanlings.