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Targeting worming to promote horse health and performance

Controlling worms is an important aspect of equine health, but one that is often poorly understood.

Targeted worming methods aim to promote horse health, ensure consistent performance and protect against resistance to wormers.

Worming methods have changed in recent years, these changes aim to promote horse health, ensure consistent performance and protect against resistance to wormers.


Yearly Monitoring Package Worm egg count submission form

Why do we need to change?

Traditionally worming products have been used periodically throughout the year regardless of worm burden, this is called interval dosing. The use of wormers in this way leads to horses receiving wormers they don’t always need, promotes resistance in worm populations and costs more financially. It is recommended that targeted worming is best practice and should be undertaken where possible. With targeted worming we use faecal worm egg counts (WEC), to decide if your horse requires worming and if so which wormer is best for your horse’s worm burden.

Faecal samples are easy to obtain and will be processed in our hospital laboratory to obtain the results. Targeted worming aims to improve your horse health whilst maintaining the effectiveness of wormers.

What is resistance?

Resistance to wormers is a widespread and ongoing problem in the UK. Resistance occurs when a large proportion of worms on a pasture are not killed by the wormer being used. Resistance to wormers can have severe consequences in the affected animal. Resistance is not something that can be reversed so prevention is the only cure.

The main causes of resistance to wormers in horses are:

  • Too frequent / unnecessary use of wormers
  • Under-dosing / Under-estimating a horses
  • Using an inappropriate wormer


If we suspect resistance to a particular wormer it can be tested for.

How the process of targeted worming works

The following points will guide you through the submission of a faecal sample.

  1. You will be asked to collect a sample of faeces from your horse’s droppings every 8-10 weeks throughout grazing season.
  2. The sample should consist of 3 pinches of faeces from different parts of a fresh dropping, the combined volume doesn’t not need to be bigger then a golf ball.
  3. For yards with multiple horses, it is best that all the horses that share the same grazing have samples submitted at the same time to allow all the horses to be tested simultaneously. For multiple submissions of co-grazing animals please submit then all on one form.
  4. These samples along with the accompany submission form will then need to be dropped into the hospital for analysis.
  5. We will contact you via email after reviewing the history form and the worm egg count results to provide the most accurate advice for worming your horse.


The need to worm your horse can be greatly reduced by following as many of the following steps that are appropriate for your yard

  1. Avoid overgrazing and overstocking
  2. Do not move horses for at least 14 days after worming. Treating horse and putting onto ‘clean’ pasture (dose and move) is not recommended as this is the fastest way to develop resistance.
  3. Clear fields of droppings at least a few times a week and do not spread horse manure on fields that horses graze

Types of wormers

There are many types of worming products out there; often these products contain 1 or 2 of the active ingredients below. If you have any questions regarding which wormer you should be using don’t hesitate to contact the hospital.

Ivermectin: Treats most stages of redworm and roundworm.

Moxidectin: Treats encysted red worm larvae and roundworm. Not to be used in foals.

Pyrantel:Can be used in animals older then 4 weeks old. Double dose will treat tapeworm. Also treats adult redworm and large roundworm.

Praziquantel: effective against tapeworms only

Fenbendazole: Used for 5 consecutive days to treat encysted red worm larvae

Also effective against large and small redworm and large roundworm.