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Pasture management an often-forgotten role in management of worms

In this article, Natascha Meunier, Beef HealthCheck Programme Manager, provides advice to farmers on parasite control in the grazing season.

The advice for treating cattle for worms over the grazing period has previously been to dose at set intervals to prevent an increase in worms over the season.

While this has worked well in most cases, it also creates conditions for the development of anthelmintic (wormer) resistance, often as a result of treating more frequently than is needed.

Resistance is present when the wormers no longer kill the target parasites or worms effectively and we need to be responsible in using wormers to ensure that they remain effective for as long as possible.

Rather than dosing at set intervals, it is better practice to use an evidence-based approach taking into account the risk of disease or losses that depends on:

  • Environmental conditions;
  • Immunity and thrive of the animals;
  • Indicators like faecal egg counts (dung samples);
  • Pasture management.
Hoose (lungworm)

We also need to be mindful of hoose (lungworm), as the best worm treatment plans may need to change if the animals are coughing and hoose is suspected.

Most of the worm lifecycle is outside of the animals, so they are highly dependent on environmental conditions.

They survive and develop quickly in the warm, damp conditions that are typical of Irish summers.

Recent dry spells mean that fewer worm larvae are likely to survive on the pastures and less frequent worming is probably needed until a few weeks after favourable wet conditions return.

The treatment plans should be adjusted based on the rainfall and temperature in the season.

Pasture management

Pasture management plays an often-forgotten role in the management of worms.

But if done well, could possibly remove the need for wormer treatments in many cases, although liver fluke treatments may still be needed going into housing. It is important that you also consult your vet.

Higher-risk pastures are those that have been recently grazed by young stock, for example, in the previous autumn.

These high-risk pastures are best avoided by calves, instead, alternating calf pastures year on year, or grazing sheep or adult cattle in the high-risk areas.

Adult animals have usually developed immunity to stomach and gut worms, if they have been exposed previously, so do not need wormer treatments unless they are high-yielding animals or fail to thrive.

Adults do not develop immunity to liver fluke and will need treatment for these parasites if they are present on the farm.

Dung samples can be useful to measure faecal egg counts. These tests give the number of stomach or gut worm eggs detected in the dung and, when requested, whether fluke eggs are present or not.


Many factors can influence the presence of eggs, so there are some considerations when interpreting the results.

For example, adult worms need to be present to produce eggs.

Development to an adult can take 3-4 weeks for stomach or gut worms and 12 weeks for liver fluke, during which time an animal may be infected, but the worm egg count is negative.

Lung worm, liver fluke and rumen fluke cause most of the damage to animals before they develop into adults, so in these cases, negative tests do not rule out these parasites causing a problem.

Worm eggs counts are better used as an indicator of pasture worm burden with repeated pooled samples throughout the season which can help find the optimum time for wormer treatments.

Repeated testing gives more information, rather than a once-off sample.

Your vet can advise you on when best to take samples and on interpreting the results.

Free parasite control consult

A veterinary consultation on parasite control (Parasite Control TASAH) is available to all Irish cattle and sheep farmers, and those who took part last year have been re-enrolled in 2023. The programme funds a free veterinary consult and two faecal samples for worm egg counts.

Over 600 veterinary practitioners are trained and participating in the programme, making it convenient for farmers to sign up as they are usually able to use their local veterinary practice.

Farmers can register for the Parasite Control TASAH via AHI’s website or with their veterinary practitioner.

Farmers who are already registered should follow up with their veterinary practitioner to book their farm visit and sampling to ensure completion before the programme closing date of October 31st, 2023.

Article: Free on-farm vet consult to review parasite control & faecal testing

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