In the last few weeks, we’ve received reports from Starcross of immature fluke being found in sheep as a cause of death on postmortem, which is quite early into the season. The point in the year at which we start seeing immature fluke causing acute disease in sheep is dependent mostly on the weather. Years with a higher-than-average rainfall through spring and summer provide more habitat for the mud snails on which the fluke are dependent for their lifecycle, so with more mud snails come more baby fluke on pasture and earlier in the year. Given that there is typically at least a three-week lag on disease symptoms from picking up these baby fluke, disease popping up in early august tells us that this is likely to be a high-risk autumn for fluke. Mild winters, also make it much easier for the snails to survive the winter, which together with wetter summers are contributing to a change in the dynamics of fluke incidence. In drought years, the dry weather forces the mud snails to hide underground until the rain returns as their habitat dries up, which can be very helpful in reducing the risk of liver fluke later in the summer, autumn and winter. Two consecutive wet summers with a mild winter in between (as we’ve just had) are a recipe for higher fluke risk.

Admittedly, Starcross takes submissions from all over Devon and Cornwall, so its not to say that everywhere is at immediate risk. However, if you have sheep grazing on higher risk pastures, then you ought to be particularly vigilant this year for signs of disease: weight loss, diarrhoea, anaemia, bottle jaw and death.

What do we consider to be high risk pastures? Any with mud snail habitat! Typical mud snail (or ‘flukey’) habitat tends to be areas that become waterlogged and boggy, characterised by rushes and open patches of mud. The snails like wet conditions, but not underwater, bare mud not recently disturbed, and open areas that are not shaded by hedges, trees or long vegetation. Such areas include depressions caused by tractor tyre ruts, poaching and natural landscape features, cleared drainage ditches, banks on the sides of streams or ponds and soft ground around leaking water troughs, taps or broken water pipes. River meadows that are prone to flooding offer the additional risk of having fluke-infected snails washed onto them from other farms upstream – they are excellent floaters.

Medium risk areas of pasture that you cannot avoid using, such as around ponds, drained ditches and muddy riverbanks, can be fenced off to reduce the risk of exposure to fluke cysts on pasture. Leaky troughs or broken water pipes should be fixed as soon as possible. High risk pastures where problem terrain cannot simply be fenced off, such as those with streams running through the middle of them, or those that drain poorly with extensive rushes growing, would ideally not be used for grazing sheep from late summer onwards, apart from in very dry years. If possible, use these types of meadows for grazing second season and adult cattle as they are much less likely to suffer acute disease and can instead be treated for chronic fluke during housing if necessary.

Testing for fluke at this point in the year (late summer and autumn) can be tricky as there won’t yet be any adult fluke laying eggs for us to find on dung sampling, and likely won’t be many until November at least. Postmortem any sudden or suspicious deaths, as it is possible to find scarring on the liver at this stage from immature fluke burrowing through the liver. Otherwise, we are dependent on blood testing first season calves or lambs for fluke antibodies to try and detect exposure – but this can be quite hit and miss.

Remember that the only flukicide which can kill immature fluke at this early stage in the season is triclabendazole, so use products containing this for treating and controlling fluke in consultation with your vet. As we progress further into autumn and winter, we are more likely to be dealing with late immature and mature fluke which can be treated effectively with other products which are often cheaper. Triclabendazole products should be used only during the autumn months and when fluke is known to be on farm, as resistance to this product leaves you with no other option for treating acute fluke.