Control of liver fluke – plans for Autumn Diana Williams, University of Liverpool

As we move through November, putting in place effective fluke control for sheep and cattle is very important, especially for farmers in the north of England, where rainfall tends to be high and permanent pasture provides ideal conditions for the snail intermediate host, to thrive.

The liver fluke life cycle is complicated and very different to that of gut roundworms.  Liver fluke relies on an intermediate host, a tiny snail that lives in muddy, marshy ground, around the edges of ponds, ditches, streams and even water troughs, if the ground is soft and poached.

The parasite develops and multiplies in the snail.  It takes around 6-8 weeks for the liver fluke to mature in the snail, it then leaves the snail and forms tiny cysts on the vegetation growing around damp, muddy areas.  In Britain, most of the development in the snail happens in the summer months and the cysts are released onto pasture in the early autumn.  If it is dry and hot, release of the parasite from the snail may be delayed.

In the Autumn, stock graze on contaminated grass.  Control now is important to prevent losses, particularly in sheep.  Fluke infection also leads to weight loss or poor weight gain, and reduced milk yield in dairy and suckler cows.

This Autumn, NADIS are predicting a medium risk of fluke in Northwest England and low risk of fluke in Northeast England.  These forecasts are based on rainfall and temperatures in May-September.  We have had a very wet October, so this risk may increase with infections occurring a bit later than normal this year

None of the treatments used for fluke have a preventative effect.  They will kill the parasite present in the animal at the time of treatment but none of the treatments protect against reinfection.  This means the timing of treatment is very important.  Treating too early is a waste of money, and potentially increases the development of resistance to treatments.  Waiting too long, risks losses in sheep, thin cows and extended finishing times.

In order to get the timing of treatment right, diagnosing when your stock become infected is very important. Then you can pinpoint treatments to the right groups of animals at the right time. It is also important to choose the right specific veterinary medicine to treat your stock.

For sheep, the best diagnostic test in the Autumn, is a blood test to measure antibodies.  Ideally take bloods from 10 of this year’s lambs.  These animals will only test positive if they have picked up infection this Autumn.  Older ewes may carry over antibodies from previous years.  Lambs should be grazed on similar pasture as the main ewe group.

If test comes back positive (one or more animal is positive), treat lambs and ewes.

Treatment at this time of year should target immature fluke, products containing triclabendazole are ideal, but resistance to triclabendazole is widespread.  Alternatively, products containing closantel can be used in early Autumn, they will target young stages of fluke.

For cattle, a good time to treat is around housing.  Again, test by taking blood samples from this year’s young stock and use the results to guide treatment.  If cattle are outwintered, take dung samples in December/January and check for eggs or use the coproantigen test.  Once eggs are detected, it means adult parasites are present so you can treat with products containing clorsulon, nitroxynil or closantel.  Keep a check on their weights, weight loss is a good indication of fluke infection.

For all treatments, be careful to check withhold periods, especially if stock are likely to go to market, and for dairy farmers, check to see if they are licensed for use in milking cows.

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