There is a saying: “If you can’t measure it, you can’t manage it”.
One key tool to monitor what is happening with worms in your animals is a Faecal egg Count (FEC). It is an estimate of the number of egg-laying adult worms in an animal’s gut. A FEC on its own doesn’t show what species of worms are there. FECs can be used to help assess:
- Whether animals need drenching.
- Whether a drench has worked or not.
- How contaminated is the pasture that animals have been grazing (how quickly they are becoming re-infected).
- Whether an animal is sick because of worms.
Is one FEC testing method better than another?
The short answer is no. There have been some recent scientific evaluations of the different FEC methods in common use, and while there are some minor differences, none are enough to throw one method out.
So what methods are available? Many veterinary clinics run an in-house FEC service, or they may send the samples to a commercial laboratory. Some farmers have learned to do their own counts and have a microscope to do their own FEC testing. Alternatively, there are commercially available, automated FEC systems enabling rapid on-farm or in-clinic testing. It is expected we will see a couple more companies available in New Zealand later in the year.
Whether you use the original McMaster technique with a microscope in your woolshed or more automated systems, the important part is that you are monitoring.
What is a Faecal Egg Count?
Faecal egg counts are a guide to the number of worms inside animals. They are not a perfect tool, but they are the most practical option we have available to get an estimate of worm burden inside an animal.
It is important to interpret FECs in light of all other information available. The trend in FECs can often be just as helpful as the absolute numbers, whatever the FEC testing method. Repeat FEC monitoring of a mob of animals often gives better information than one count in isolation. This is particularly true for composite FECs.
There are limitations with faecal egg counting:
- Only mature female worms lay eggs, so mature male and immature worms are not detected.
- Egg output from female worms varies throughout the day and eggs are not evenly distributed through the faeces of the animal.
- Worm species vary in how many eggs they lay each day.
- Identification of worms is not straightforward – the eggs of several species are largely indistinguishable to the human eye. However, the development of several A.I-assisted egg identification systems looks set to remove this limitation.
Keep these limitations in mind when interpreting FECs. If you tested the exact same faecal samples using different FEC testing methods, you would not get the exact same answer. Even if you use the same method on the same lump of poo, you won’t get the exact same number! Generally, the absolute number is less important than the trend that FECs are showing.
When to do a FEC?
- To test if worms are part of the reason that an animal or mob is sick or performing poorly.
- To check drench effectiveness. Collect samples 10 days (7–14 days) after treatment and test FECs (they should be zero or very close to it!)
- Deciding when to drench again – check FECs 28 days after a drench. If low, then retest again in 1-2 weeks. This is a safe way of extending drench intervals and providing refugia.
- Double-checking your grazing plan – If the FEC is high at 28 days your animals are quickly becoming reinfected; their grazing area is heavily contaminated, and/or they are being underfed.
Talk to your animal health advisor about the best time to monitor. This will vary depending on your farm system and the reason for FEC testing.
Individual FECs or composite FECs?
For individual FECs; 10+ samples are collected and processed separately, to give a FEC in eggs per gram (epg) from each animal.
The advantage of individual testing is the ability to assess the range of FECs in the mob. Sometimes an ‘average’ is reflective of most animals, but more often the ‘average’ is skewed by high FECs from a small number on individuals. Individual samples cost more and take longer to process. Individual sampling is recommended when checking the effectiveness of a drench.
For composite FECs; 15–30 samples are collected. Ideally, a standard volume is collected from each dung pat, and the samples are thoroughly mixed together. One or more subsamples from the bulk mixed sample is processed and read as an average FEC for the mob.
Composite testing is faster and cheaper but doesn’t give you as much detail. Repeating counts (say 3) on the same bulk sample and increasing the frequency of monitoring to determine the FEC trend will give you more information.
When you’ve got your FEC results, what do they mean?
When the counts are very low or very high, it is usually pretty straightforward to determine what to do. But when counts are in the middle range, that can be trickier to interpret.
For more information check out this webpage: Interpreting Faecal Egg Counts.
Whether testing at home or through another provider, please ensure to discuss your FEC testing results with your trusted animal health advisor. The answer may not be clear, and your decision needs to include information around when animals were last drenched, age and life stage of the animals, feed available and body condition of the stock.
Can you do FEC testing in both sheep and cattle?
Yes, you can.
The relationship between FEC results and actual worm burden is stronger in sheep, and calves to 6 months of age than in older cattle.
Faecal Egg Counts can give you confidence to put the drench gun down. Utilise FEC testing alongside animal appearance and performance to check the success of your worm management plan. Collect some poos today!