10-step guide to taking a sheep faecal egg count

What a FEC can do:

  • Help develop a more effective and sustainable worm control programme
  • Give a good indication of the level of adult egg-laying worms present in the animal
  • Provide an indicator of infection with the main gut worms
  • Identify eggs of nematodirus worm species
  • Give a useful guide to the level of worm affecting the group
  • Be used to detect whether wormers are fully effective

A faecal egg count (FEC) is used to monitor worm burdens in sheep.

Not only does it help determine if sheep need treating for gut worms, but doing a follow-up count after drenching enables you to check the product has worked.

FECs are a vital tool in the armoury against growing drug resistance, because they allow you to monitor the efficacy of treatments and prevent the overuse of products at times when they are not needed.

Independent sheep consultant Catherine Nakielny offers advice on taking FEC samples and explains how the results are determined at the lab.

Step 1

Gather the sheep into the corner of the field and hold them there for about five to 10 minutes.

This should be plenty of time to get fresh samples. 

You can also collect fresh samples when sheep are being handled in the pens.


Step 2

Wearing a pair of disposable gloves, pick up fresh dung samples and pool them into a sealable, plastic bag. Samples should be soft and ideally still warm to touch.

See also: More how to guides


Some laboratories prefer samples to be sent individually so that they can then be grouped together by weighing the same amount from each, so check beforehand.

Aim to collect samples from at least 10% of the group. It is important the same amount of faeces is collected from each individual tested.

See also: How to check your sheep flock for fluke

Samples need to be about the size of a 50p coin. To ensure consistency, pick them up with a measuring spoon.


If you are testing post treatment you must wait for a minimum of seven days, although timing vary depending on what treatment you have used (see right).

When to test post-treatment

  • Yellow drench – 7 days post treatment
  • White drench – 10-14 days post treatment
  • Clear drench – 14-16 days post treatment

Dr Nakielny says the mistake many farmers make is to assume that sheep with dirty back ends will have a higher worm count and therefore they only test these ones.

However, she says dirty back ends can be caused by different factors – such as lush grass or mineral deficiency – so it is important to sample the entire group.

Step 3

The next step is to get your samples analysed. Dr Nakielny recommends speaking to the farm vet first to discuss available options.

Many vets offer a FEC service, so call to find out. If they can’t do it in-house, the practice can send samples to a national laboratory.

What a FEC can’t do:

  • Remove the need to monitor performance and look out for clinical signs in individual animals
  • Tell you what species of gut worms are present (apart from nematodirus species)
  • Detect whether any coccidia oocysts present are a pathogenic species
  • Pick up early reinfection after treatment (it takes 17-21 days for worms to develop into egg laying adults)

This has the benefit that further tests can be carried out for different parasites if necessary. Alternatively there are commercial companies which carry out these tests.

Step 4

As soon as the samples arrive at the lab they are put into a refrigerator if they are not counted immediately.

“The samples need to be kept cool. At 7C or more the eggs will start hatching,” explains Dr Nakielny.

However, samples should not be frozen as this will damage the eggs, she adds.

Step 5

Samples are weighed so the correct amount of fluid (salt and water) can be added to make the eggs float so they are visible under the microscope. This is then mixed into liquid form so the light can penetrate the solution under the microscope.

On the day Dr Nakielny weighed 10g of faeces and added 30ml of water and 200ml of salt solution.

Step 6

The solution is then put through a sieve to remove any debris (grass and dirt) and the liquid is drained into a beaker.


Step 7

Using a pipette a small amount of liquid is extracted from the beaker.

Extracting a sample with a pipette for a FEC
















Step 8

This is then transferred on to a glass slide, which has a counting chamber.


Step 9

The slide is examined under a microscope where eggs can be identified and counted within the chambers of the slide.

Those on the outside of the square are ignored.


Step 10

The total number of eggs counted is then multiplied depending on the dilution rate to give the total number of eggs per gramme of faeces.

The volume of the sample counted will depend on the type of slide used but is typically 0.15ml. Dr Nakielny multiplied the results by 30 using the technique explained here.

See also: Find out how one farmer has eradicated liver fluke

Strongyle eggs under the microscope

“The actual process of counting worm eggs is really quite simple. It is, however, the interpretation which requires further knowledge of the parasite lifecycle and risk factors for the animal.

“It is always advisable to discuss results with a vet or animal health adviser when beginning to use FEC results in a worming programme.

Factors such as age, condition, forage quality, time of year and weather are just a few of the considerations which need to be made.”

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