Worm egg counts

Worm egg counting involved a process whereby a known amount of fresh dung is put through a precise process, allowing eggs produced by roundworms to be identified and counted under a microscope.  To improve accuracy, each sample is counted twice and an average taken.  A calculation then converts this count to the number of eggs per gram of faeces.  This number of eggs per gram is a standard measure and allows us to estimate the egg producing adult worm burden in the horse's intestines.  By conducting routine worm egg counts (WECs) we can build up a picture of each horse's susceptibility to roundworms, gauge the effectiveness of your current worming program and make recommendations to reduce wormer resistance.

Worm egg counts can be used:

  • to assess the level of burden of infestation in normal horses;
  • as part of a strategic worming program to try and minimise wormer resistance and cut down on the cost of worming;
  • to identify whether a worm infestation is a likely cause in the clinical assessment and identification of a horse with weight loss, diarrhoea or colic;
  • to assess whether the worms in your horse are resistant to the wormers you are using, by performing a faecal egg count reduction test;
  • to make sure your current worming program is effective;
  • as an estimate of pasture contamination; and
  • to assess the worm burden of a new horse introduced onto a new premises (or prior to purchase).

More information

WECs should only be done during the grazing season. There is little value in the winter months when the majority of the larvae in the horse are encysted in the gut wall.

As well as the correct season, timing of WECs is also important. When utilising them in a strategic worming program they should be done no sooner than the normal egg reappearance period (ERP) following the previous wormer.

Class Product names ERP
Benzimadazole Panacur 4-6 weeks
Pyrantel Exodus, Strongid P, Pyratape P

4-6 weeks

Ivermectin Eqvalan, Equimax, Noromectin, Maximec, Eraquell

8-10 weeks

Moxidectin Equest, Pramox

13 weeks

Faecal egg count reduction tests assess the level of resistance to a particular wormer. To undertake this test a number of horses with high WECs should be tested just prior to and then 14 days following worming and the two results compared.

While WECs are revolutionising the way we create worming control programs, the Equitait WISE worming program is mindful of their limitations. They do not give an assessment of encysted larvae, likewise they will not detect pin worms or bots and will only very rarely detect tapeworm. For a more accurate way of detecting the tapeworm burden an ELISA blood sample is recommended. If a tapeworm ELISA is not performed horses should be treated for tapeworms at least once a year. Encysted larvae are treated once a year in the winter currently with a moxidectin product (eg Equest) which can be combined with praziquantel to also treat for tapeworms (eg Pramox).

A one-off negative WEC does not guarantee the absence of a worm burden throughout the rest of the year which is why we recommend a series of WECs throughout the grazing season to ensure we are not placing animals under increased risk.

The counts are given in eggs per gram (epg). For the purpose of the WISE worming program a WEC of 200 epg or fewer is considered low. Counts between 200 and 1000 epg are considered moderate and anything above 1,000 is considered high. Horses with counts of 200 or less should be left untreated. Horses with counts greater than 200 should be treated with an appropriate wormer. If a number of horses have a particularly high WECs then a faecal egg count reduction test performing WECs again 10-14 days following treatment will help to identify if a proportion of the worms are resistant to that wormer.

Sending samples to Equitait

If you are sending a sample to Equitait for worm egg counting, please click here for a submission form and further details on sending us your sample.