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Faecal Egg Counting

For sustainable worm control, sheep should only be wormed if there is a worm burden present.

Understanding whether there is a worm burden in the lamb before treating is a key step towards sustainable worm control, avoiding unnecessary wormer treatments (when there are no worms there), but also never ‘missing the boat’ and treating after the damage has been done.

Applying a ‘test don’t guess’ approach benefits both the animal and your pocket.

Regular FECs throughout the grazing season will keep on top of the worming needs for lambs and show the best time to use Zolvix™ as a break dose.


Ideally, faecal egg counts (FECs), taken every 3-4 weeks throughout the grazing season, should be used to determine when to start dosing lambs and how often to do so. FECs can also be used to determine if a given group/class of wormer is working on an individual farm. This is called drench testing.


Taking a FEC is simple and quick once you know what to do. It involves taking 10 or more samples of fresh faeces (dung) ideally less than one hour old, from a mob of sheep. Samples should be kept cool and delivered to a vet or laboratory for analysis within 48 hours. Some agricultural merchants also offer FecPak services in their branches – ask you prescriber for more details. The results will give the number of worm eggs in the combined samples presented as ‘eggs per gram’ (EPG) of faeces. The number is an indication of the number of adult worms present in the gut of the sheep and can be used to:

  • Tell in a treatment has been successful
  • Help tell if an animal needs to be treated
  • Provide an indication of the level of contamination on a pasture

To check whether a treatment has been effective, a drench check should be completed. The length of time after treatment to do this test is dependent on the wormer group used.

  • 2-LV (yellow wormer group): 7 days
  • 1-BZ (white wormer group e.g. Rycoben™), 3-ML (clear wormer group e.g. Dectomax™), 4-AD (orange wormer group Zolvix™): 14 days

Doing a drench check provides an indication of how effective the treatment has been and does not automatically mean you have resistance.


For further information on testing for wormer resistance visit SCOPS.

Find out how you can help preserve the older three classes of wormer (1-BZ, 2-LV and 3-ML) by replacing one of your normal wormer treatments in the mid-late season with Zolvix™.

Watch this short explanation of how to do a FEC:

Zolvix™ 25mg/ml oral solution is a broad spectrum anthelmintic for the treatment and control of gastro-intestinal nematode infections and associated diseases in sheep including lambs, hoggets, breeding rams and ewes. Contains monepantel. Legal category: POM-VPS. Information regarding the side effects, precautions, warnings and contra-indications can be found in product packaging and leaflets; further information can also be found in the Summary of Product Characteristics. Advice should be sought from the medicine prescriber prior to use. Zolvix, Elanco and the diagonal bar logo are trademarks of Elanco or its affiliates. Use medicines responsibly (http://www.noah.co.uk/responsible). PM-UK-21-0726.