Horse Worming


Worming your horse is very important, however resistance to available wormers is getting worse.


The most common worms are:

  • Large Strongles (large redworms): These migrate through arteries causing weight loss, severe damage and colic. Luckily these worms are still susceptible to most wormers currently in use.
  • Small Strongles (small redworm, cyathostomins): The larvae burrow into the gut lining where they can lie dormant as encysted larvae. In 50% of cases when the larvae emerge from the gut wall in spring massive inflammation, diarrhoea, colic and death can even occur. These are therefore difficult to identify from faecal samples. A blood test can be used to detect the presence of these.
  • Roundworms (Parascaris equorum): Commonly found in young horses, older horses develop immunity. Diarrhoea and colic with subsequent weight loss can occur.
  • Tapeworm (Anoplocephala perfoliata): Blockage with these worms at the ileocaecal junction and caecal wall causes colic. Identification in faeces is not reliable and a blood or saliva test is available.
  • Pin worms (Oxyuris equi): Cause itching around the bottom from the eggs being laid in this region. These are usually identified from taking sellotape stripes of the eggs.

Regular worming without knowing which worms are present creates a worm resistant population that can’t then be treated. This can potentially cause colic, poor nutrient absorption and poor performance. A short animation video can be viewed at that explains this further.


New thoughts on how to worm and when

We strongly advise to collect a faecal sample from your horse during the grazing season and have it analysed for how many eggs are present. If the egg burden isn’t high then worming is contraindicated. If the number of eggs is above the reasonable threshold then your vet will recommend a suitable wormer.

Tapeworm and the small redworm CANNOT be detected via looking for eggs in faeces. A blood test is available to test for both these worms but a new saliva test is now available for tapeworm detection.


Other ways of reducing worms:

Pasture management

  • Poo picking the field is still a really good method of reducing the worm and egg burden around.
  • Not to over graze or have a high stocking density, ideally each horse needs 3.5 acres to graze.

Biological control

  • The fungi nematophagus will predate on worm larvae.


Benefits to you by testing for the worms in your horse

Reduced cost of wormers by using only the correct ones at the correct times if at all!