21st Century worm control – are you getting it right?

What do you know about worm control? Guidance on the best ways to control worms in horses has changed in recent years and it’s important to move with the times to help keep our horses healthy. The best way to do this is to talk to your vet or Suitably Qualified Person (SQP) at your local equestrian store.

So what’s changed about worm control?

horse-feedingBlanket worming every horse on the yard every few months is now regarded as very old fashioned and not very effective. In fact it can be counter-productive. The modern way is to tailor a specific plan for each horse; conduct regular faecal worm egg counts (FWECs) to guide targeted dosing in the summer and dose strategically for specific worms that don’t show in egg counts.1 There are important scientific reasons for the changes.

What’s wrong with the old worm control method?

In the same way that antibiotics are becoming less effective in humans and in animals, scientists have discovered that worms are becoming resistant to the drugs in some wormers and can survive, despite the horse being wormed. The development of these resistant worms increases if wormers are used indiscriminately.1 Currently, there are only four different drugs used in equine wormers so it is vitally important for us to preserve their effectiveness by using them in a responsible, targeted way.

The role of vets and SQPs

Vets are highly qualified to advise you on all aspects of horse care but did you know that SQPs also have to take special qualifications in order to advise and prescribe wormers? SQPs have to maintain their qualification by attending lectures and proving their knowledge throughout each year.  If they don’t keep up to date then their qualification will lapse and they will be unable to prescribe wormers.

Vets and SQPs have the knowledge to guide you on the most up-to-date methods of worm control and it’s important to ask their advice before making any decisions about worming your horse.

So what is 21st Century worm control?

  • Faecal worm egg counts should be used every 8-12 weeks during the grazing season from around March to October and horses treated according to the results.2
  • Encysted small redworm (don’t show up in FWECs) should be targeted in adult horses once a year in the late autumn or early winter using a single dose of moxidectin or a five-day course of fenbendazole. There is widespread evidence of resistance in small redworm to fenbendazole, including the five-day dose so a resistance test is recommended before using it.1
  • Tapeworm (don’t show up in FWECs) should be targeted twice a year, usually in the autumn and the spring using a single dose of praziquantel or a double dose of pyrantel or a specific tapeworm test conducted.2
  • Bots (don’t show up in FWECs) should be treated annually after the ‘first frost’
  • Weigh before worming to ensure you buy and give the right amount of wormer. Under-dosing can encourage worms to become resistant to the wormer you use and not be killed by it, creating a strain of resistant worms on your yard.
  • Use faecal egg count reduction tests during the grazing season: The best way to ensure that your wormers are working properly is to ask your vet to perform a faecal egg count reduction test each year. This involves taking a FWEC immediately before and two weeks after worming to assess the level of worm eggs being shed.
  • Keep pasture clean: Daily poo-picking, regular rotation and resting of fields and cross grazing with sheep or cattle will help keep pasture worm burdens under control.
  • Keep a record: so that you have a history of the wormers used and the results of tests. Share this information with your vet or SQP to avoid overuse of the same types of wormer.
  • Seek advice: Never be afraid to ask for help. Always speak to your vet or SQP to discuss the best worm control programme for your horse and his environment

Why can’t you tell me which brand of wormer I need to use?

In the same way as for antibiotics, it is illegal to advertise wormers to horse owners. Only the medicines prescriber, namely your vet or SQP, can advise you on which brand of wormer your horse requires. They have to ask certain questions to make sure that the correct wormer is prescribed at the right time of year and that it is the most suitable one for your horse’s individual needs.


  1. AAEP (2016) Parasite control guidelines.
  2. Hallowell- Evans and Hallowell (2017) Vet Times, April 24
  3. Matthews (2008) Equine Veterinary Education, p 552-560
  4. Proudman and Matthews, In Practice (2000) 22, 90-97

Article by Dr Wendy Talbot BVSC Cert EM (Int Med) DECEIM MRCVS

Wendy graduated from Bristol University in 1999. She then went on to complete a residency at Liverpool University and holds a European Diploma in Equine Internal Medicine. After working in practice for 13 years, she joined Zoetis in 2012 as the National Equine Veterinary Manager.

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