Liver Fluke

Liver fluke is a very common parasitic infection of cattle and sheep ( evidence of this can be seen at post mortem inspection of cattle and sheep in the abbatoir). It is a disease of great economic and of course animal health significance in Ireland.

It is helpful to have an idea of how this parasite lives to better understand the ways you can control the disease.

Warm wet conditions are ideal for this parasite to thrive. The mud snail acts as an intermediate host for the parasite and warm wet conditions lead to an increase in the mud snail population. Warm wet conditions are also necessary for fluke eggs to hatch.



If June and July are wet, then all the fluke eggs that have been passed onto the pasture the previous grazing season hatch at the same time as the surge in the snail population, leading to a massive increase in immature fluke on the pasture.
Conversely, if the weather in May–July is dry or cold, fewer snails appear, fewer fluke eggs hatch and levels of contamination in the autumn are much lower. Clinical fasciolosis resulting from summer infection of snails arises usually from ingestion of large numbers of metacercariae over a short period of time in July–October.

After cattle or sheep eat these immature fluke while grazing, it takes up to three months for them to develop into adult fluke in the cowʼs liver and biliary system ( bile ducts). Therefore you may only start to notice evidence of a chronic problem from November on.

Sometimes snails become infected in Autumn, then hibernate over Winter, start shedding immature fluke onto the pasture in Spring, thus infesting cattle or sheep in the Springtime.

The three main risk factors are

Previous fluke history on the farm.

Environments where the mud snail thrives – around streams and ponds, leaky watertroughs, wet poached areas.

Weather conditions which favour mud snails – a mild wet autumn and winter followed by a wet summer will lead to a very high fluke risk
What will you see in your herd/ flock?

Acute disease
Results in rapid condition loss and sudden deaths. More common in sheep than cattle.

Occurs 1-3 weeks after infection in sheep; 1-5 weeks in cattle and is the result of damage caused by the migration of large numbers of immature flukes through the liver.

Normally seen late summer and autumn but occasionally into winter due to animals ingesting large numbers of immature fluke off pastures.

Sub acute disease
Fewer deaths than acute disease, usually results in loss of condition and performance during the autumn and early winter.

Caused by immature fluke damaging the liver as they migrate.

Sheep normally affected 4-7 weeks post infection and cattle 6-9 weeks post infection.

Chronic disease
Chronic disease is caused by adult fluke feeding and egg laying in the bile ducts and often occurs later in the autumn and winter.

Results in anaemia ( each adult liver fluke can take up to 0.5ml of blood per day)

Loss of condition and bottle jaw (due to reduced blood proteins) are common Liver fluke can cause immunosuppression and so increase the susceptibility of cattle to IBR or salmonellosis

It can increase the risk of clostridial disease such as Black disease ( make sure clostridial vaccinations up to date.

It can increase the risk of metabolic disease in sheep (twin lamb or hypocalcemia)

History of fluke on the farm and clinical signs

Investigate deaths. Post mortem examination is an extremely important way of diagnosing a fluke problem.

Faecal sample to detect fluke eggs ( eggs only detected when adult egg laying fluke are present )

Treating Liver Fluke
It is important to get veterinary advice when choosing a flukicide.

There are different products available with differing activities against the various stages of liver fluke.

Where infection risk is high and you need to kill immature fluke, triclabendazole is the drug to use.

In spring treat to remove adult liver fluke to reduce egg output onto pasture. Use a product that only kills adult fluke, saving those which kill immatures for the autumn.

Ensure that two doses are given where indicated.

Be aware of the risk of re infection if animals are put back on high risk grazing areas. If possible manage this by moving to low risk grazing or housing. Otherwise further fluke treatments will be necessary.

Currently, the only licensed flukicides for use in dairy cows and replacement heifers are albendazole and oxyclozanide – both have a 72 – hour milk withdrawal.

Triclabendazole can be used in dry cows.

Pay attention to withdrawal periods for meat and milk.


Abbatoir feedback on livers.

Faecal samples to detect fluke eggs ( only useful when adult egg laying fluke present).

Blood testing ( serology) for antibodies.

In dairy herds bulk milk testing for fluke antibodies is a very useful tool to assess the level of fluke in the herd and also the response to treatment with flukicides.

Performance indicators – body condition score, liveweight gains.

In dairy herds, liver fluke will depress milk protein and heavy infestations can decrease milk yield

In suckler cows, it can be a cause of weight loss and recumbency prior to calving

Plan ahead to avoid high risk areas on the farm at peak risk periods to reduce infection levels on the farm in the future.

Assess the risks every year ( ie mild Winter followed by warm wet Summer bad) and use abbatoir feedback.

Choose the right flukicide. Triclabendazole for when killing immature fluke is a priority. Consider alternatives at other times.
Dose correctly to the weight of the animal. Take particular care with pour on products for cattle.

Check for fluke resistance using faecal samples post treatment – on some farms triclabendazole may no longer be fully effective
Quarantine and treat bought in animals