High risk of liver fluke infection in sheep and cattle this autumn and winter, 2024/2025

According to Parasitologists working at the Agri-Food and Biosciences Institute (AFBI), farmers the need to be aware of the risk of liver fluke infection in cattle and sheep during autumn and winter.

Although this year saw a decrease in both rainfall and average temperature from May to September in comparison to last year, calculations using climatic data from four monitored sites across NI indicate that a high prevalence of fluke infection in stock is likely, if appropriate measures are not taken. 

From May to September 2024 the average total rainfall was 23.22% lower than in 2023, representing a 10% decrease below the average Northern Ireland rainfall for that period of the year.

The mean monthly temperature from May to September 2024 was 13.0˚C, which is lower than in 2023, but represents an increase of 2.30% over the mean average temperature for NI in the summer months.

A mean day/night temperature of 10˚C or higher is necessary, both for the snail intermediate host to breed and for the fluke larvae to develop within the snails. A temperature of 10˚C is also the minimum at which fluke eggs will develop and hatch.

Considering the mean temperature and rainfall for May to September 2024, multiplication of snails will have continued unabated on those pastures which are poorly drained and remain wet all year round.

Liver fluke disease can occur in either acute or chronic forms. The acute form occurs in sheep and is caused by the migration of large numbers of immature flukes through the liver. Acute liver fluke is often fatal and has serious welfare implications.

Signs of severe infections include distended painful abdomen, anaemia and sudden death. In less severe cases, poor production and growth, coupled with reduced appetite and abdominal pain are apparent. Chronic liver fluke disease is more common than the acute form and occurs in both sheep and cattle, usually during the winter and spring, although infection can persist throughout the year. Affected animals may exhibit ‘bottle jaw’ (swelling under the jaw).

Fluke infection can cause a reduction of 5-15% in the milk yield of dairy cows and reduction of growth in fattening lambs and cattle. It is therefore a source of considerable financial loss to the local agricultural industry. Fluke infections in dairy cattle can also predispose to metabolic conditions such as ketosis and infectious diseases such as salmonellosis. The same is likely to be true for sheep. Migrating liver fluke can also predispose animals to the clostridial infection, Black disease, and care should be taken to ensure that cattle and sheep in fluke-affected areas are fully vaccinated against this disease.

All farmers should review their fluke control measures at this time of year. Access to snail habitats (wet and poorly drained areas) should be reduced, or sheep taken off the land and housed or moved to new clean pasture. However, in most cases, control will be based on the strategic use of anthelmintics, employing a product effective against the life cycle stages likely to be present in the flock or herd at the time of treatment. This is particularly important in autumn when acute fluke infection occurs in sheep and pick-up of infection by sheep and cattle is still taking place.

At this time of year, a product effective against both immature and mature forms is needed. Use of such a product on out-wintered sheep once or twice in autumn, with possible follow up in January, coupled with a treatment effective against adult flukes in early spring, should significantly reduce the fluke burden on individual farms.

Treatment of chronic (adult) infections in cattle as well as sheep during the winter or early spring is important to help reduce pasture contamination with fluke eggs. Use of an anthelmintic with activity mainly against adult flukes may be sufficient in these circumstances. However, the flukicide programme used has to be on a ‘know-your-farm’ basis and no one set of recommendations will cover all flocks or herds.

Farmers need to be aware that resistance to fluke treatments is an emerging problem and has been detected in Northern Ireland. On some premises, products containing triclabendazole (the only flukicide currently licensed in UK and Ireland that is effective against the immature stages of liver fluke, causing acute fasciolosis in sheep) have been used almost exclusively for a number of years. On such farms it is possible that triclabendazole-containing products may now be less effective in controlling fluke infection, and for treating acutely-ill animals. The effectiveness of anthelmintic treatment on individual farms can be checked by taking dung samples three to four weeks after treatment and submitting them, through a veterinary surgeon, for laboratory examination.

In recent years, stomach (rumen) flukes have also become common in sheep and cattle in NI, and this is particularly the case in fluke-prone areas. Adult rumen flukes are less damaging to sheep and cattle than liver flukes, but heavy infections of immature flukes may cause diarrhoea, ill-thrift and, exceptionally, death in young animals.

If you suspect that stomach fluke infection may be a problem on your farm, you should contact your veterinary surgeon to arrange for appropriate laboratory testing, and to discuss treatment options.

Advice on the most suitable anthelmintic and other control measures can be obtained from your veterinary surgeon. The AFBI veterinary laboratories at Stormont and Omagh can assist your veterinary surgeon by testing dung and blood samples from livestock for evidence of fluke infection and associated liver damage. Further information on liver fluke disease in cattle and sheep may be found on the AFBI website

Notes to editors: 

AFBI is an arms-length body of DAERA delivering research and development, diagnostic and analytical testing, emergency response capability and expert scientific advice for DAERA and other government departments, public bodies and commercial companies in Northern Ireland, and further afield.

AFBI’s Vision is “Advancing the Local and Global Agri-Food Sectors Through Scientific Excellence”.

AFBI’s core areas:

• Leading improvements in the agri-food industry to improve its sustainability;
• Protecting animal, plant and human health;
• Enhancing the natural and marine environment.

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