Worm egg counting

(WEC or WormTest)

Worm egg counting is one of the most useful worm management tools a sheep or goat producer can use. You will also see this test referred to as a WormTest or simply a WEC. In the past, the term FEC (Faecal Egg Count) was also used.

Adult worms in the gastrointestinal tract of sheep or goats produce eggs that are passed out of the intestinal tract with the host’s dung. A worm egg count is the number of worm eggs in a sample of sheep or goat dung and is an indicator of the type and size of the worm burden present in the host. 

The result of a worm egg count is standardized by weight and expressed as 'eggs per gram' (epg) of dung, with the main results often divided between strongyle eggs (including most of the significant worm species such as barber’s pole worm, brown stomach and black scour worm) and Nematodirus eggs.

The actual worm egg count at which the worms become a problem varies with the worm species present as well as other factors including the season, and the age, condition and pregnancy status of the sheep or goat. You can use the WormBoss Drench Decision Guide for your region to assist you to decide when to drench based on a worm egg count.

Most of the significant worm species have eggs that appear similar during a worm egg count, so a larval culture is required to identify the species present in the sample, adding further value to the test result.

Worm egg counts are a practical and quite accurate tool to estimate the burden of adult worms in monitored animals or to check the overall worm status of a mob or group to decide if a therapeutic treatment is necessary (that is, a treatment that will directly benefit the animals treated). They are certainly much more accurate than visual assessment and will identify an emerging problem long before any visual signs appear, at which time significant production loss will already be occurring.

They will also help to decide if previous treatments were effective or assess the levels of worm egg contamination being put into paddocks.

Note, however, that there are times when a strategic drench is recommended, which does not use a worm egg count. Strategic treatments are generally at a specific time of the year, or sheep or goat management event (depending on regions) that aims to lower the overall worm population for the coming months, and will be given regardless of the worm egg count or at much lower worm egg counts than for a therapeutic drench.

Collecting samples for a worm egg count

It is important to collect samples from a representative number of animals. Samples from 20 individuals provide a more accurate indication of the worm burden across a mob than 10 samples. For larger mobs, particularly where barber’s pole worm is a problem (as there can be a much wider variation in individual worm egg counts), samples from more animals are useful.

Follow this link to find more details on ‘Checking a mob of sheep of goats for worms with a WormTest, including how to collect samples.

Worm egg counts for breeding for worm resistance

Worm egg counts are also the basis for selecting worm-resistant sheep or goats. Ram or buck breeders will collect samples from individual animals, generally around or between weaning and yearling age. The results are used to calculate Australian Sheep Breeding Values for worm egg count (WEC ASBVs) or WEC EBVs in KIDPLAN for goats. Read more on breeding for worm resistance in a commercial flock or Sheep Genetics .

Conducting a worm egg count at the lab

When the dung samples arrive at a laboratory, a carefully weighed sub-sample will be taken from each of the samples. This is mixed with a known volume of saturated salt solution. A sample of this mixture is placed on a special microscope slide (Whitlock Universal or Whitlock McMaster) where the saturated salt solution makes the worm eggs float to the top of the mixture in the slide where they are easily 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.


Image: Roundworm eggs shown under a microscope Source: Anne Oakenful, NSW DPI (Worm Egg Counting Course Notes)
Image: Roundworm eggs shown under a microscope Source: Anne Oakenful, NSW DPI (Worm Egg Counting Course Notes)

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 clicking on the link below.

Click here to be redirected to the University of Sydney website to practice worm egg counting.

If you do not have 'flash player' click on the link below.

Get flash player.

Larval culture and species differentiation

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 because the eggs of many common species of sheep and goat worms cannot be differentiated during a worm egg count.

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 at about 24°C for a week to allow the eggs to hatch and develop into worm larvae.

The larvae are then examined under the microscope by experienced laboratory technicians who can identify the species of the worm larvae and who give a result describing the proportion of each worm species in the dung samples.


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

Some farmers do their own worm egg counts; it is not difficult to learn.

Items required for egg counting:

  • Laboratory compound microscope. Hobby ones are not suitable as the special egg counting slide/chamber may not fit under the lens. The microscope does not need to be expensive or fancy; the old monocular microscopes found in school science laboratories can be quite satisfactory, but binocular microscopes (two eyepieces) are less tiring to use if you do a lot of egg counts.
    • A mechanical (movable) stage is also desirable rather than having to push the counting chamber around on a fixed stage using your fingers. Most compound microscopes will have a 10x (10 times magnification) eyepiece (at the top), and one or more objectives (the lenses down the bottom). A 4x objective (for routine counting) and a 10x objective (for closer examination) are required.
    • Take care if your microscope has larger objectives as well, e.g. 100x ‘oil immersion’ lenses. Inadvertently using these with the counting chamber could result in the chamber cracking.
    • Most capital cities have a company that reconditions then sells old microscopes (often in bulk lots from universities and schools). Try looking for microscope or optical suppliers in your nearest capital city.
    • Course providers usually provide guidance on buying microscopes.
    • Microscopes need to be maintained and protected from dust and thoroughly cleaned of saturated salt solution, which can be corrosive to metal and lenses. 

Image: Compound/biological microscope. Source: NSW DPI Profarm Worm Egg Counting course notes.
Image: Compound/biological microscope. Source: NSW DPI Profarm Worm Egg Counting course notes.

  • Egg-counting slide (e.g. Whitlock, McMaster). These last many years if care is taken with them. 
  • Electronic scales for weighing out faeces (unless using a displacement method). Kitchen scales measuring to 1 gram are available through department and kitchen stores starting at about $25.
  • Beakers, jars and mixing implements for preparing faecal solutions and for mixing up saturated salt.
  • Battery hydrometer ($5–10 at auto stores) for checking specific gravity of salt solutions (not essential).
  • Pipette or similar for loading the counting chamber.
  • Salt e.g. pool salt or table salt.

Suppliers of microscopes, egg-counting chambers or complete kits

  • Egg counting slides are available from JA Whitlock & Co (approx. $130 in December 2014), PO Box 51, Eastwood NSW 2122, phone 02 9638 1142. Email.
  • ‘FecPak’ kit Veterinary Health Research, Armidale NSW. Email.
  • Eggsact kit, NSW, email.
  • FEC Source slides, USA. Email.
  • Microscopes: Most capital cities have a company that reconditions then sells old microscopes (often in bulk lots from universities and schools). Try looking for microscope or optical suppliers in your nearest capital city.

Training

Training in how to do worm egg counting is available through some state departments and other training organisations, including:

NSW DPI PROfarm workshop:
A 1-day workshop costing from $330 dollars using DPI microscopes, held regularly at Camden/Menangle, Tamworth (and sometimes other locations). Check details and cost when registering.

RuralBiz Training—Online workshop in Worm Egg Counting:
A 1-day workshop (run bimonthly) costing $320 per person (plus equipment costs). You participate from your home computer over the internet and during the training you connect your microscope to your computer (with a special eyepiece provided by RuralBiz Training) and then to the instructor via the internet. The RuralBiz course also covers a nationally accredited unit (AHCLSK504A Develop livestock health and welfare strategies). If the participant completes the two short assessment tasks after the workshop, they receive a nationally recognised statement of attainment.

Having done the training you will need to commit to regularly collecting the required number of samples and following the correct egg counting procedures in order to get a valid result. Periodically check the accuracy of your worm egg counts (quality control) by conducting comparison testing—ask a worm egg counting laboratory how you should do this.

The most expensive items for DIY worm egg counting are the microscope and the counting chamber (and your time). If you take good care of these and do regular worm egg counts, you will pay for these items many times over.

However, DIY egg counting is not for everyone. In some cases it may be a better use of your time to get a laboratory to do your egg counting for you.

If you want to know the species of worms present, you will have to send dung samples to a laboratory offering that service (larval culture and differentiation).

Note that these courses teach how to do round worm (nematode) egg counts, which fortunately is the most useful worm egg counting technique to learn. Different and more involved methods are required to do liver and stomach fluke egg counts.

The following publication provides detailed information on standard parasitological techniques (nematodes):

Hutchinson GW (2009).  Nematode Parasites of Small Ruminants, Camelids and Cattle: Diagnosis with Emphasis on Anthelmintic Efficacy and Resistance Testing.

This is also a good source of information even if you do not plan to do your own egg counts.