Faecal Egg Counts measure the eggs per gram of faeces (epg) that pass through a sheep and hence the worm load. Note that the epg coming out today are from worms that were ingested by the sheep about three weeks ago.

First decide what you are going to do with the Faecal Egg Count (FEC) information. There are two options:
(a) To decide whether the sheep need a drench or not.
(b) To decide which animals to keep if breeding for worm resistance.
You want a much more accurate measure for (b) than you do for (a).

Deciding whether to drench or not

This question arises because you have seen some signs of worms in the sheep, the most common being that the animals are scouring and not doing well. You may even have had some lamb deaths. It's very important to find out if worms were the cause and not something else, and an FEC is the place to start.

1. Collecting the sample

  • Pick up some fresh samples from the ground - usually from around 5-10 different sheep.  Ten sheep is an ideal number.

2. Storing the sample

  • Place them in a lidded container or sealable plastic bag and mix them up as this is a "composite" sample and you'll get one FEC estimate from it.
  • You don't need to rush the samples to the vets. They'll keep in a domestic fridge (preferably clearly marked and not near food!) at around 4-5ºC for a week. But it's a good idea to get them to the veterinarian or process them yourself as soon as convenient.

3. Interpreting the results

  • The general rule is that a 'trigger level" of 500 epg is generally accepted to decide whether to drench or not. If the composite sample was above 500 epg, then the veterinarian would recommend to drench all the sheep.
  • Now things have changed, and you are advised to leave the top (most healthy looking) 5-10% undrenched, to allow "susceptible" worms to survive to reduce the speed with which the worm population in the sheep become resistant to anthelmintics. This is called using "refugia" - i.e. the worms are in refugia.

4. Which drench to use

  • Here you must get advice from your veterinarian. Just buying any drench off the shelf is now far too risky with rapidly increasing drench resistance in worms to specific chemicals. What you buy depends on so many things, especially the state of drench resistance on your farm, which you won't know until you check it out.
  • To check if a drench is working, collect a composite FEC then drench with a specific product from one of the three chemical families. After an interval repeats the FEC to see how many of the worms were killed. If less than 95% were killed the worms in your sheep are resistant to that particular product.
  • Contact your veterinarian to make sure you do this correctly - and how to proceed to get more information. A full "Faecal Egg Count Reduction Test (FECRT) may be recommended. This is more involved, takes time and costs money. From it, you can find which species of worms are involved.

5. Correcting Faecal Egg Count (FEC) for Faecal Consistency Score (FCS).

  • It's very important that the consistency of the faeces is taken into account as wet sloppy faeces pass through the digestive tract faster than drier faeces. So when they emerge there will be less worm epg in soft faeces than in firm drier ones and a correction is needed for accurate decisions.
  • This is vitally important for breeding so the correct animals are kept as replacements. Here are the correction factors used:
    • Marbles - multiply FEC x 1
    • Hand grenades - multiply FEC x 2
    • Plops - multiply FEC x 3
    • Slops - multiply FEC x 4
    • Scour - multiply FEC x 5

See Dalton's book for full details. D.C.Dalton (2007). "Internal parasites of sheep and their control - now and in the future". 3rd Edition with cartoons by David Henshaw.To decide which animals to keep for breeding

The aim here is to breed sheep that don't need dagging and don't need drenching. They are genetically "resistant" to worms. For this, you need an FEC on individual animals, especially rams, as we know that resistance to dags and worms is inherited.

Sampling individual animals

  • If you only have a few animals then you can wait and watch them pass faeces, and collect that. But with large numbers, this is too slow, and you need to collect samples from the sheep's rectum.
  • Use a finger (preferably with a rubber glove) and draw out at least 5grams. This may take two insertions. If no faeces can be obtained wait for about 15 minutes. Putting the sheep on pasture will also help to move the digesta along the gut.
  • I recommend a plastic probe which is less stressful on both sheep and the operator. It easily collects 5g in one insertion and your hands are kept clean.

Scoring Faecal Consistency when sampling

  • When the probe is withdrawn you can usually see the formation of the faeces. You'll see folds of the marbles and hand grenades which will be very firm. If these are not clearly visible, then you can judge the speed with which the faeces run out of the sample pottle. Marbles and hand grenades will not run out and the others will - scour running out the fastest.
  • If you want to see which sheep have marbles only, feel these with your finger and you don't need to withdraw any faeces from the sheep.


  • Each animal will need a number and you can incorporate the FCS into the Identification number. For example, 345(1) is sheep 345 that has produced marbles (FCS1). This makes it easy when you get the results back to multiply the FEC by the FCS score in a column for decision making.

Laboratory measurements

  • If you use a veterinary laboratory for your FEC measurements, it's very important to tell them that a more accurate estimate is needed as you want the information for breeding decisions. This they do by increasing the dilution of the sample so no eggs are missed.
  • A good way to test their accuracy (and yours too if you do your own) is to send in a dummy sample made up of the same sheep. Mix the sample well and divide it into two sub-samples giving them separate identification. There should be no more than 100 epg difference between each to know that the method used is accurate.