While no two years are the same for parasite control, knowing what worms are on a farm and having an idea when they could pose an issue can help farmers manage them and avoid costly production losses.

According to animal health specialist Tony Morris from Wynnstay and vet Ally Anderson from Zoetis, the main worm threats and their management, are as follows.

Read more: Do you know what kinds of worms you have in your sheep?

Lambs are the priority for worm control due to their lack of immunity. The focus of worm control is to minimise the effect of internal parasites on their performance. To achieve this, a range of management tactics should be used alongside the careful use of anthelmintics. Understanding which worms pose a threat and when they are a risk can help farmers in their worm control plan.

The main worm species affecting lambs are:

1. Nematodirus (Nematodirus battus)

When is it a threat?

The risk period begins when the weather suddenly changes from cold winter frost to warmer spring weather. If this coincides with the time when lambs are starting to take in significant amounts of grass (over about six-weeks-old), the result can be devastating, with a high level of mortality possible.

Nematodirus larvae take eight to nine months to develop, with eggs not typically developing into infective larvae until the following spring, when they can be picked up by 6-12-week-old lambs and cause significant losses.

The larvae cause damage in the lamb’s gut, so predicting when a hatch will occur is the key to knowing when to treat.

Signs

Nematodirus can strike very quickly and because the damage is done by large numbers of immature larvae that are not producing eggs, faecal egg counts (FECs) are not a reliable indicator of risk.

Signs include:

o Sudden onset diarrhoea.

o Faecal staining of tail and perineum.

o Dull/depressed lambs.

o Lambs which stop sucking.

o Dehydration.

o Loss of body condition.

Management

Using forecasts such as the SCOPS forecast (https://www.scops.org.uk/forecasts/nematodirus-forecast/) and tools such as the Zoetis Parasite Watch Scheme (www.parasitewatch.co.uk) are helpful as an early warning sign and can indicate if and when susceptible lambs need treating.

Farmers can also reduce the risks by grazing pastures that lambs did not graze in the preceding spring. However, if this is not possible and lambs are at risk, the advice is to use a white drench.

2. Teladorsagia – small brown stomach

When is it a threat?

Worm populations tend to build up through mid-spring and summer.

Signs

At low levels, they can reduce the appetite in lambs, which will affect growth rates. However, when levels peak in mid-summer, the risk of more severe symptoms such as diarrhoea and even death can occur.

Management

Farmers can reduce the risk by grazing weaned lambs on pasture that hasn’t had sheep on earlier in the season.

Research has also found that treating selected ewes with CYDECTIN 2% long-acting at lambing to suppress the spring rise (the relaxation of a ewe’s immunity around lambing) cuts the egg output from ewes leading to lowered pasture contamination1. This means that the lambs will be faced with a lower worm challenge and so should require fewer treatments.

However, when using Cydectin 2% long-acting, the Zoetis and SCOPS guidelines must be followed. This includes only treating a proportion of the ewes, i.e. ewes in poorer body condition or with a high worm egg count, and not using the product when it has already been used in the same year, such as when it was used for scab control.

Faecal egg counts should also be used along with, clinical signs and body condition to determine whether treatment is needed.

3. Trichostrongyles – the black scour worm

When is it a threat?

This is most commonly seen in the autumn in store lambs but can occur earlier.

Signs

It typically causes rapid weight loss, scouring and death, particularly in poorer lambs.

Management

Use FECs to monitor the level of infestation throughout the autumn and winter months. Ewes in good condition can help ‘clean the pasture’ to reduce worm burdens on autumn finishing pastures. Co grazing with cattle can also be helpful, as cattle can be used to ‘hoover’ up the larvae.

BOX: Farmers can sign-up to receive 2022 Parasite Watch alerts for free by going to www.parasitewatch.co.uk