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This is one of the most useful worm management tools a sheep producer can use.

A worm egg count is a count of the number of worm eggs in a sample of sheep dung.

The result is usually expressed as 'eggs per gram' (epg) of dung with the main results often divided between strongyle (including most of the significant worm species such as barbers pole worm, brown stomach and black scour worm) and Nematodirus eggs.

The actual number at which the worms become a problem varies with the worm species present.

For example, a worm egg count of 500 eggs per gram (epg) of barbers pole worm is not as significant as 300 epg of Trichostrongylus vitrinus, one of the scour worms.

Conducting a larval culture, which will identify all the species present in the sample, can further refine this result.

Worm egg counts are an important practical tool to estimate the burden of adult worms in monitored sheep.

A worm egg count is a much more accurate diagnostic tool than visual assessment and will identify an emerging problem long before any visual symptoms appear.

Worm egg counts are a useful guide to check the overall worm status of a mob to decide if treatment is necessary, to decide if previous treatments were effective or to assess the levels of worm contamination being put into paddocks.

Individual sheep worm egg counts can also be used as the basis for selecting worm resistant sheep.

• Worm egg counts (WEC)
• Worm typing (larval culture and differentiation)
• Do it yourself

 Worm egg counts (WEC)

Collecting the sample:
There are 2 ways dung samples can be collected - freshly deposited dung off the ground or directly from the rectum of the sheep.

If collecting for normal monitoring of a mob, the sheep can be quietly held against a fence for 10 – 20 minutes, allowed to walk off and fresh dung collected off the ground, taking care not to collect too much dirt and other debris with the sample.

Often sheep are 'on camp' in the early afternoon (noon to 1.00pm) and this is a good time to quietly approach the mob, get them to stand for a short time before moving them off camp and then collect samples from the fresh dung piles.

Faecal samples can be collected directly from the rectum of individual sheep with a gloved finger.

This is the preferred technique when it is important to have individually identified samples, such as when selecting animals for worm resistance, and when collecting post-treatment during a Faecal Egg Count Reduction Test (FECRT or resistance test) so that exact groups of origin are known.

The collected samples should be sent to the laboratory as soon as possible after collection. Contact your local veterinarian, sheep consultant or laboratory to discuss specific sampling and laboratory requirements for worm egg count.

Doing the count:
When the samples arrive at the laboratory, a carefully weighed sub-sample will be taken from each of the samples.

This is mixed with a saturated salt solution. A sample of this mixture is placed on a special microscope slide (Whitlock Universal or Whitlock McMaster). The saturated salt solution makes the worm eggs float to the top of the mixture in the slide where they are counted. The number of eggs is multiplied by a sample weight and dilution factor to arrive at the 'eggs per gram' (epg) figure in the results.

View worm eggs

Image supplied by Dr R Woodgate, Western Australia Department of Agriculture

Virtual worm egg counting

This virtual worm egg counting graphic was developed by Associate Professor Nick Sangster, University of Sydney and his contribution to WormBoss is gratefully acknowledged.

Practice worm egg counting by opening a flash file in a new window.
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 Worm typing (larval culture and differentiation)

It is difficult to differentiate the eggs of many common species of sheep worms during a worm egg count.

When it is important to know exactly which species of strongyle worms are present (e.g. when the presence of barber’s pole worm is being checked or after a drench resistance test) a worm larval culture and species differentiation is carried out.

The collected dung remaining after the worm egg count has been completed is bulked together in a jar, mixed with a substance called vermiculite to help aerate the dung and then incubated in an oven for a few days to allow the eggs to hatch and develop into worm larvae. Trained laboratory technicians can then tell the species of the worm larvae and give a result describing the proportion of each worm species in the dung samples that were from the different worm species.

Worm larvae

Image supplied by Dr R Woodgate, Western Australia Department of Agriculture

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 Do your own worm egg counts

Some farmers do their own worm egg counts. Learning to do worm egg counts is not difficult. You will need a laboratory microscope (hobby ones are not suitable), an egg-counting chamber, some beakers and mixing implements and a supply of saturated salt solution.

Egg counting chambers are available from JA Whitlock & Co, PO Box 51, Eastwood NSW 2122, phone 61 2 9638 1142, website: http://www.whitlock.com.au/slides/JAWCO_Home.htm

Training is available through some state Departments and other training organisations. You will also need the discipline to regularly collect the required number of samples and to sit down and follow the correct procedures on each sample if you are going to get a credible result. However, it is a fact that most sheep producers who start out doing their own worm egg counting go back to paying for a professional service.

There are also commercially available worm egg counting kits. You should check the accuracy of your worm egg counts by conducting comparison testing which is available from some accredited laboratories.

If you want to know the species of worms present, you will have to send dung samples to a laboratory offering that service.

NSW Department of Primary Industries offers a one-day training course on faecal worm egg counting.

For further information  
web:  NSW Department of Primary Industries
tel: 1800 025 520