Q&A: Everything you need to know about gastro-intestinal worms

There are more than 20 different species of worms and fluke that affect cattle in the UK.

Knowing what they are, when they pose a risk to your stock and how you can control them is vital for minimising production losses.

Dave Armstrong, a vet with Zoetis, explains what gastrointestinal worms are, how to minimise the risk and how to spot if you have a problem.

What are they?

The main species affecting cattle include:

  • The small brown stomach worm (Ostertagia)
  • Barber’s Pole worm (Haemonchus)
  • The small intestinal worm (Cooperia)

Propensity to cause disease varies depends on worm species, the number of worms present and other factors such as the age of the animal, nutritional status and body condition.

In cattle, the small brown stomach worm (Ostertagia) and small intestinal worm (Cooperia) tend to be the most common. This is particularly an issue in younger animals in their first grazing season as they haven’t built up immunity to worms.

Cooperia in cattle is the main contributor to faecal worm egg counts, whereas Ostertagia tends to cause more disease.

Where are they found/how do animals become infected?

Animals become infected by grazing pasture that contains the worm larvae. Once ingested by cattle, the larvae develop into adult worms in the host within about 14 days.

These adult worms then produce eggs, which are then excreted out in the dung of the host. The whole cycle in the host tends to take about 16-21 days.

The eggs then develop into larvae on the pasture over 2-12 weeks and the whole cycle begins again.

See also: Five things you need to know about lungworm before spring turnout

When are they most prevalent?

For most gastrointestinal worms, spring onwards is when you will see problems.

What are the symptoms of gastrointestinal worms in cattle?

Cattle tend to be less obviously affected by worms than sheep, often due to tolerating a higher burden and the development of immunity, if they are exposed as young animals. However, their effect should not be underestimated.

Cattle infected with worms can have lower weight gain and performance. It can also reduce an animal’s ability to fight off other diseases.

Gastrointestinal worms typically affect young calves during their first grazing season, causing gastroenteritis, diarrhoea and weight loss.

How can you prevent worm infections?

Prevention and control methods will depend on the worm in question.

In order to prevent/try and minimise the risk of infection, knowing what you have on your farm and regularly performing faecal egg counts is the first step.  

Having a planned grazing strategy in place can also help. For example, pasture contamination can be reduced by grazing cattle and sheep together. This reduces the stocking density of the host species.

Rotating grazing between cattle and sheep during the season is another way to dilute the worm burden.

Regular faecal egg count tests can alert you to problems before they arise. However, it’s important they are done regularly, so action can be taken before production loss occurs.

Likewise, knowing what worms are causing problems in your can help farmers, vets and suitably qualified persons (SQPs) make informed decisions about what to treat and when.

There are several places you can find out about this, such as the NADIS parasite forecast and Zoetis’s Parasite Watch site.

Before reaching for any wormer it’s important to know the resistance status of your farm.

Reduced drench performance due to resistance leads to more worms surviving and, ultimately, reduced performance. Conducting a post-drench test is a crude, simple test, but can give an indication of any resistance or under-dosing issues in a herd.

How should you decide what treatments to use?

A worm control plan should be constructed with your vet, adviser or SQP Things to consider include:

  • Which worms are present on your farm
  • Meat/milk withdrawal periods
  • Age of the animal
  • Whether there’s mixed grazing

It is vital treatments are administered at the right time and dose and should be based on informed decisions made with your SQP, vet or adviser. They should not be based solely on the time of year.