Horse Worming Schedule

We receive quite a few enquiries from clients about a horse worming schedule. Read our guide to find out more.

Horse Worming

Resistance to equine wormers is a problem that affects us all and is likely to become an ever more serious issue in the future. Resistance is promoted every time a wormer is used, as some of the worms in a horse are likely to be naturally resistant to the wormer. Thus, when the wormer is used, the sensitive ones are killed and resistant ones left behind to multiply on your fields. Over time, there is significant risk that this resistant population will build up and result in wide-spread wormer resistance across the UK. This issue is important if you just keep one horse or are on a big livery yard. Resistance to cyathostomins (small redworm) has been reported in all types of wormers.

Young Horses

Youngsters (less than 18 months) are more at risk of high worm burdens as their immunity has not developed fully yet, so we need to be more careful with this age group. They are also at risk of disease caused by Parascaris equorum (ascarids; grow up to 10cm long) which require specific treatment. Please contact us for specific advice from one of our vets about worm management in youngsters.

Worm Egg Counts (WECs)

To avoid the spread of resistance we strongly recommend the use of WECs to detect which horses actually need worming. 80% of horses do not need worming during the Spring and Summer months. WECs are not useful over winter months as the small redworm encyst in the gut wall inside the horse and are therefore not producing eggs detectable in the poo. We recommend WECs are done every 2-3 months from March to October depending on risk and history. If a horse has a very high WEC result, we may recommend repeating the WEC 2 weeks after worming to ensure it has been effective.

How to collect poo for WEC

Collect a sample from fresh poo passed within the previous 12 hours. Take small amounts from several different parts of the pile to make a sample which is about a handful in total. Mix it up, place it all in a sealable bag and expel the air before posting/dropping it at one of our branches as soon as you can. Once at the practice it will go in the fridge to keep it fresh until counting.


In winter we currently advise all horses are treated with Equest to treat any encysted small roundworm as well as others that could be a problem.


High burdens of tapeworm are relatively uncommon but can cause serious colic when present in large numbers. Traditionally horses have been treated for tapeworm twice a year, but again, this risks development of resistance over time. We now recommend the use of the Equisal saliva test for tapeworm once or twice a year, so we only treat horses that have high numbers present. Equisal tests can be ordered from our practice, come with instructions and are performed by yourself. We will then report the result back to you and advise on any treatment necessary.


This is an issue in a minority of horses, but can be really unpleasant for badly affected horses. They will scratch their tail heads and back end causing hair loss and sometimes sores. Please give us a call to discuss treatment if you suspect your horse has pinworm.

Horse worming schedule throughout the year: (This may vary between yards depending on various factors).

What else can be done to keep worm numbers low?

  • Isolate new horses and worm with Equest Pramox before turning out with others. We recommend new horses are isolated for 2-3 weeks on arrival anyway to prevent spread of disease.
  • Remove dung from fields at least twice weekly (significantly reduces worm numbers).
  • Fields must be rested for 9 months to consider them ‘safe’.
  • Co-grazing with sheep/cattle can reduce worm numbers in horses.
  • Tell vet if your horse co-grazes with donkeys as they can pick up lungworm.
  • Don’t harrow in the UK. It isn’t hot enough here and just spreads the worms out!

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