Worm Management

There is no one size fits all – your farm is unique

The purpose of any worm management programme is to maintain or improve profitability by reducing the exposure, especially of young animals, to worms – by limiting the number of infective larvae on pasture.

The key factor is knowing what is happening with worms on your farm.

The key tools to determine this are:

  • Faecal egg counts (FEC)
  • Faecal egg count reduction test (FECRT)
  • Identifying worm species by using faecal larval cultures (FLC)
  • Monitoring production indicators such as weight gain, milk production, body condition score

Other worm management strategies may include:

  • Stock and pasture management plans to reduce exposure
  • Ensure good nutrition
  • Adequate disease prevention programmes/plans
  • Breeding resistant/resilient animals
  • Use appropriate drenching strategies

A drench check
This test is a simple and quick way to check if a drench being used is effective.
It is done by simply doing a Faecal Egg Count on faeces from drenched animals about ten days after the drench was given.
If there are worm eggs present on this test it can mean several things:

  • It can mean that the drench was not fully effective and has left some worms still laying eggs.
  • That the FEC was extremely high before the test and the residual egg count at ten days is not unexpected.
  • That the animals were not drenched correctly, either the dose rate was insufficient or the administration was not correct or not all animals were drenched.

A drench check is a useful tool to use over the season to check the effectiveness of the drenching process.
Any investigation of drench resistance requires a more complete test than this ie a faecal egg count reduction test.

Faecal Egg Counting

Gastrointestinal worms lay eggs that are excreted in the faeces of the host animal. Counting the concentration of eggs in the faeces will provide a good indication of the number of adult worms residing in that host. The test should be used with other tools for making decisions. This is because the concentration of worm eggs in the faeces is influenced by a number of factors other than how many worms there are in the host.

Examples of these variables are:

  • worms in mature animals lay fewer eggs than worms in young animals;
  • different worm species produce different numbers of eggs per adult worm;
  • the health of the host can change the egg laying capacity of adult worms;
  • worm infestations less than three weeks old will not be reflected in a FEC because the worms will not have reached egg laying maturity.

Faecal Egg Counting is done by washing faeces in saline to float the eggs out. These can then be counted under the microscope. A lot more information can be gained by culturing the faeces with the worm eggs in them to identify the species and number of worms present. The worm eggs of most of the worm species common in our livestock look the same under the microscope, hence the need to culture the faeces to identify the worm species present.

Faecal Egg Counting can be used as a diagnostic tool when investigating poor growth, ill health or diarrhoea. The test is most widely used to help make drench decisions. When used with other information it is a very useful tool for managing worms. The test is also used for testing the effectiveness of anthelmintics. This test is called a drench check or a faecal egg count reduction test.

Faecal Egg Count Reduction Test (FECRT)

This is a test using Faecal Egg Counting to measure the effectiveness of drenches. It compares the change in the FEC before drenching or with no drenching, with the FEC after drenching. The drenched animals are FEC’ed about ten days after being drenched. This FEC is compared to either a FEC before they were drenched or a FEC from undrenched animals at the ten days. The result is reported as the percentage that the egg count has been reduced.

A complete test requires a larval culture of the faeces from undrenched animals and from the drenched animals ten days after drenching. This shows which worm species are resistant and which are susceptible.

The results from this test must be treated with caution if not all worm species are present before testing or if the FEC before testing is not very high.

Integrated grazing management

  • Production benefits arise from lower levels of challenge of young stock in particular.
  • Plan to create low levels of larval challenge – use stock movement, grazing history, pasture species, weather, and stock type and classes to match nutritional needs.
  • Use a paddock diary – stock class mapping as part of the planning process. This will enable you to identify where a challenge is from and anticipate how to deal with it.
  • It is preferable, not to use the farm paddocks for the same purposes year after year – for example, to always fatten lambs. All paddocks should be exposed to all stock classes during the course of a year so that the worm population on the farm is continually mixed up rather than having some paddocks populated with worms that have all originated from frequently drenched stock.