SCOPS & COWS: Test before you treat sheep for liver fluke this autumn

Advice on autumn liver fluke control in sheep and cattle for RAMAs and Veterinarians.

Changing practice may be the best way

As fluke risk can vary considerably from year to year, between regions and even between neighbouring farms, every farm needs to be considered individually. We strongly advise RAMAs and Veterinarians to recommend diagnostic testing for liver fluke before treating. This will allow you to tailor the best control advice to each farm, which product to prescribe, and when it should be used.

Why to test before treating

Autumn is typically a high risk time for fluke, and therefore an important time to diagnose and treat stock for fluke to prevent serious disease or production losses. Animals pick up infection from the pasture in autumn. Stock may be exposed to larger numbers of immature fluke than earlier in the year which develop in the cattle and sheep.

This year, COWS/SCOPS experts suggest that fluke challenge will be very variable across the country as a result of the very dry spring in many areas followed by a warm, wet summer.

For sheep, treatment must be timed well to target the immature stages that cause acute fasciolosis. Diagnosing infection before treatment is vital, so treatment is not wasted when there is no fluke burden in the animal. By treating appropriately, this will reduce the selection for the development of resistance.

For cattle, whilst it is common practice for farmers to treat with a combination product at housing for liver fluke, GI nematodes and ectoparasites, it is important to assess the situation on each farm first. Most combination products only kill late immature fluke. Treating at housing, when early immature fluke are still present will not remove the whole fluke burden. Again testing to confirm there is a fluke burden before treating is vital.

Testing in the autumn and which treatments to prescribe

Testing strategies will depend on the type of stock kept and the fluke risk.

For sheep, using sentinel lambs and blood testing (i.e.testing for fluke antibodies by ELISA) once a month from August to December can pinpoint when they become infected. As soon as they sero-convert (i.e. become positive), the whole flock/group should be treated with a product that targets immature fluke. For farms with a low fluke challenge, treating immediately upon sero-conversion may not be necessary. In this case it is important to discuss the results and the farm’s previous fluke history with the farmer. A copro-antigen test or a repeat blood can be performed on that group to confirm when treatment is needed. Products containing triclabendazole are very useful at this time of year, unless the farm has confirmed triclabendazole resistance. Alternatively closantel-containing products could be prescribed.

For cattle, consider the likely fluke challenge;

• Farms with a history of fluke could test for fluke antibodies by ELISA in first season grazing calves at housing as sentinel animals.
• For older groups of cattle or farms with a lower fluke challenge, assess the likely risk of infection and monitor growth rates. The coproantigen test can be used about 6 weeks after housing. Samples from 10 individual animals should be submitted to the laboratory for testing if using the copro-antigen test.

At this time, a product containing triclabendazole or closantel could be prescribed if these tests are positive. Nitroxynil can also be an option if stock have been housed for more than 8 weeks.

By Christmas, (assuming cattle were housed in October), most fluke will be adults. A faecal egg count or the coproantigen test could be used. A product targeting adult fluke such as clorsulon, or oxyclozanide can be prescribed.

Many flukicides for cattle are only available as combination products, so discuss other parasite control with the farmer and only use combination products if indicated.

If treatment is given early after housing, then advise that the farmer should test cattle before they go out in the spring. Any residual immature fluke that survive an autumn treatment will now be adults and producing eggs. Use the coproantigen or faecal egg count to detect infection and advise a spring treatment to reduce pasture contamination. Again, if using the copro-antigen test, individual samples should be submitted for testing. A composite faecal egg count test can be used; however samples should still be submitted individually, and will be pooled by the laboratory

Always be aware of the withdrawal periods for meat and milk for any treatment given.

Risk forecasts, for example NADIS (www.nadis.org.uk/parasite-forecast.aspx), can be used to assess the infection risk across regions and from year to year to help monitor the fluke situation.

Through testing, the right product can be selected to treat the right animals at the right time to give effective and efficient fluke control.