Horse Wormers by Sara Walker

Horse Wormers

Every horse owner knows how important to follow a worming programme, but understanding what wormer to give when can be confusing.

Wormers contain several active ingredients, so it’s usually better not to dose your horse unless he actually needs it.  Develop an annual worming strategy, and pay particular attention to the danger periods.

Suggested Annual Worming Strategy - Spring

Spring can be a dangerous time of year, as worms that have been lying dormant over the winter are now coming alive. In spring, you need to take two forms of action:

  • Deal with tapeworm. Consider worming for tapeworm if your horse is at high risk of infestation. Give a wormer containing praziquantel, such as Equest Pramox, Equimax or Eqvalan Duo. As an alternative to worming, you can have your horse blood tested by a vet. However, this is sometimes misleading, as horses can show a positive result up to six months after infestation. Tapeworms aren’t particularly resistant to wormers so are easy to control, but they won’t show up on a normal worm egg count. Your horse should have at least one dose of tapeworm-effective wormer a year.
  • Do a worm egg count (see below). The technician will count the number of strongyle eggs present in the sample, which should be less than 200/gram per horse. No horse will ever be completely worm free, but a normal horse with a healthy immune system should be able to deal with a worm burden below of 200 eggs/g. If your horse's test comes back with a higher reading, then administer a suitable wormer. Most wormers will tackle redworm, but check on the packet before administration.  If you get a low test result, there’s no need to worm separately for redworm.

Worm Egg Counts (WEC)

Worm egg counts are carried out to test for the presence of redworms and are a good alternative to indiscriminate worming. Your vet can often carry out the test for a small charge; alternatively various suppliers offer a postal service. A worm egg count is normally more cost effective than buying wormers.

  • Collect a small amount of fresh faeces which has been passed within 12 – 24 hours. If the sample isn’t fresh, the eggs will already have hatched out and won’t be visible.
  • Send the sample to your tester immediately.
  • At the lab, the sample is prepared with solution and placed under a microscope for the eggs to be counted manually. If your horse has a very high egg count, for example in the 1000s range, seek immediate advice from your vet, who’ll advise a specialist worming program.  A horse with a low count need not be wormed for redworm.


  • Do a WEC in early summer, around June. If you get a result of over 200 eggs per gram, worm accordingly, otherwise, wait until autumn.


This is the most dangerous season, when your horse is at the highest risk.

  • Worm for tapeworm. All horses should be wormed for tapeworm at least annually, preferably in the autumn.
  • All horses more than a year old should also be wormed with a larvaecidal wormer such as Equest
  • Worm for redworm

You can combine all the above stages by using a ‘blanket’ wormer such as Equest Pramox or Eqvalan Duo, rather than giving three separate doses. This annual dose is particularly important if you have not yet wormed this year due to low WEC results.


Winter is the time of lowest exposure, as the worms start to regain their dormant state in cold weather. If you’ve previously had a high test result earlier in the year, it’s worth getting another WEC done in the winter to be on the safe side.

Additional Advice

  • Do not worm your horse indiscriminately, as you risk the worms developing a resistance to the wormer. Use a different wormer annually to help prevent this.
  • For youngsters under a year old, consult your vet for a tailored worming programme
  • Always wait for 8 – 12 weeks after a wormer has been given before doing your next WEC, as the residual effect of the wormer means that any worms should be dead anyway.
  • Foals need a dedicated worming programme from 8 weeks of age
  • Pregnant mares should be wormed 2 – 3 months prior to foaling


In Summary

One tapeworm wormer, two egg counts with a low result and one blanket wormer per year will protect your horse.

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