As part of our Horse Health Programme (HHP), we are keen to protect your horse against worms. This includes more than just providing free wormers – the best way to keep horses safe, now and in the future, is to practice 'targeted worming'. We explain what this means, why it is important, and how to provide safe, effective worm control year-­round.

If you need more information, just contact your local Horse Health Programme practice for expert advice. We can provide best practice, up-to­‐date recommendations on any aspect of parasite control.

Targeted worming

If you worm all your horses routinely you will be:

  • Worming horses unnecessarily
  • Encouraging development of resistance in worms
    • Exposure to wormers selects for worms that are resistant to the chemicals used
    • By avoiding routine use of wormers, we will retain a controlled worm population that is a mixture of resistant and non‐resistant strains; this is ultimately safer for horses than promoting selection of resistant worms
    • Resistance is already a serious problem worldwide.

Instead of routine worming, we recommend evidence-based worming, including:

  • Faecal worm egg counts (FWECs) 4 times/year*
    • These detect eggs of strongyle-­‐type worms (large redworms, small redworms, and roundworms) but not tapeworms
  • Horses that have egg counts of >200 eggs/gram of faeces are shedding substantial numbers of eggs onto the pasture, thereby increasing the infected pasture larval burden; it is these horses that we need to target when worming
  • Tapeworm saliva test* in autumn
  • In autumn, after the first frost, worming all horses with:
    • Moxidectin/praziquantel* if saliva test is positive
    • Moxidectin* if saliva test is negative
  • At other times, only worming horses with positive FWECs.

*included in your HHP membership.

Important worms in autumn

In autumn, we are primarily concerned about two parasites:

  • Encysted small redworms
  • Tapeworms.

Encysted small redworms

  • The larvae of these dangerous parasites:
    • Burrow into the intestinal wall, forming cysts – currently, we cannot test for this
    • Migrate out of the intestinal wall in the late winter or early spring leading to inflammation, diarrhoea, colic and, in some cases, death
    • Can be killed using a moxidectin-­‐based wormer.


  • Tapeworms infect only a minority of horses
  • Only horses with a positive tapeworm saliva test should receive treatment (praziquantel).

Important points

For safe and effective worming, follow these tips:

  • Always use the correct wormer
    • Contact your veterinary practice for advice; we supply competitively priced wormers with expert advice about which one to use
    • Do not use moxidectin-­based wormers unless you need to; overuse will encourage resistance and could lead to moxidectin becoming useless against encysted small redworms
  • Know your horse’s weight; give the correct amount of wormer
    • Under-­dosing encourages development of resistance
  • Moxidectin is toxic to pets and fish
    • Dispose of syringes correctly; avoid contamination of watercourses
  • Perform autumn worming after the first frost because:
    • Frost kills bot flies; moxidectin kills bot larvae
    • Worming after the first frost keeps horses bot-­free until the following season.

We provide FWECs as part of the HHP because they form an important part of your horse’s preventative healthcare programme. But even horses with negative FWEC results need worming in the autumn to protect them from disease caused by encysted small redworms and, potentially, tapeworms. If you are unsure about any aspect of your worming programme, contact your veterinary practice for advice.