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Liver Fluke in Cattle - why fluke risk varies

Two key factors cause the significant issues associated with liver fluke:

  • when the infectious stages (the metacercaria) first appear on the pasture ie when the challenge starts
  • the level of challenge – the number of metacercaria, the larval stage of the fluke, on the pasture

The fluke risk for each season is affected by the conditions over the months before. Different active ingredients are needed to target the different stages of fluke

It is important to assess the fluke risk by monitoring both the fluke forecast and the situation on your farm, and adjust the choice of treatment accordingly.

In most areas of the UK, temperatures during the winter months are low enough (<10C) to kill off a lot of the mud snails (the intermediate host in the life cycle of the liver fluke), leaving just a small number that burrow down into the mud and hibernate to survive the winter. These low temperatures also mean that any fluke eggs on the pasture will be dormant.


The treatment of choice for beef cattle at this time will depend on if the cattle are housed or outside over winter.

Housed cattle

If the cattle were housed in the autumn, then they will not have been able to pick up new infective cysts. If they WERE NOT treated at housing, then a faecal sample can show if any infections are present. Alternatively you can monitor any signs of fluke from abattoir returns. If the cattle WERE treated at housing, it will depend on what they were treated with, and when:

  • If the cattle were treated at the start of housing with a product that eg only kills fluke from 7 weeks of age, some fluke will still be in the cattle and could be affecting performance. If these cattle are going out in the spring, they will be carrying adult fluke that will be producing eggs that will contaminate the pasture.
  • If cattle have been housed for 10 weeks or more then a product that kills adult fluke would be appropriate.
  • The active ingredients that target adult fluke are albendazole, oxyclozanide and clorsulon.

Outwintered cattle

If cattle are out during the winter, they may require a treatment as they may have potentially ingested more fluke cysts from the pasture after their autumn fluke dose. However, as the number of infective larvae on pastures will be declining, treatments should target both immature (from 8 weeks) and adult liver fluke, or adults only depending on the local risk.

The active ingredients of choice would be:

  • For immature fluke: triclabendazole pour on, closantel or nitroxynil
  • For adult fluke: albendazole, oxyclozanide or clorsulon.


Warm and/or wet conditions: As the weather warms up in the spring, and soil temperatures rise, the fluke eggs will start to develop and the snail population will start to increase. As it gets warmer this development happens faster, so that most of the fluke eggs that landed on the pasture through the winter and spring will hatch around the end of May or beginning of June.

By this time there is usually a very healthy mud snail population, provided there has been enough rain to maintain the mud conditions they need. The miracidium, the active stage that hatches from the fluke egg, also needs wet conditions to be able to swim from the egg and find a snail to infect. Once inside the snail, the liver fluke will take around 8 weeks before the metacercaria (the stages infectious to cattle and sheep) appear on the pasture. Therefore, in warm and wet weather, the fluke eggs will hatch in May, find a snail and develop quite quickly, so that metacercaria appear on the grass in August. The fluke don’t kill the snails, so the more snails that get infected, and the longer the weather stays above 10C in the autumn, the more metacercaria will accumulate on pasture. The higher the metacercaria numbers, the higher the risk to grazing animals.

Cold and/or dry conditions: Dry or cold conditions slow down snail activity and development of the fluke, so that instead of taking 8 weeks for metacercaria to appear, it could take 3-4 months. A cold/dry spring means eggs might not hatch until the end of June, relatively few will find a snail, and those that do may take 3-4 months before metacercaria are released. Therefore, in these conditions there would be no infectious stages on the grass for livestock to pick up until October.


In the summer months, liver fluke in cattle are likely to be adult. Therefore, treatments should target adult liver fluke only. The active ingredients of choice would be albendazole, oxyclozanide or clorsulon.

Once the autumn/winter temperatures drop below 10C again, most of the snails will die off and the survivors will hibernate in the mud. No more metacercaria will be released, and as those present on grass die off over time, the numbers and the risk to grazing animals will decrease through the late winter and into the spring. As the spring grass starts to grow, and there has not yet been any snail activity, there will be no metacercaria present, and so little or no risk to grazing stock.


In the autumn/early winter, we get the highest number of early immature fluke and so need a product that kills these. The only active to kill early immature fluke - ie fluke that is under 5 weeks old is triclabendazole, the active in Combinex for Cattle™ and Fasinex 240™. Oral triclabendazole kills liver fluke down to 2 weeks old in cattle.