• Low risk but time right treatment
• Some areas are worse than others
• Regular testing vital, say experts
Liver fluke levels are forecast to be relatively low for much of the UK this winter – but experts say the risk to grazing livestock on individual farms is less predictable.
This means farmers should test to ensure they don’t treat for the problem too soon or unnecessarily, or get caught out and miss a vital treatment, say two livestock groups – the Sustainable Control of Parasites in Sheep (SCOPS) and Control of Cattle Parasites Sustainably (COWS).
The mud snail is the intermediate host for the liver fluke. And last year’s dry summer means there are fewer areas where the mud snail can survive.Without moisture, the flukes find it difficult to migrate to pasture.
But not all of the country was so dry, say livestock advisers. Even within a farm, wet, boggy areas may have allowed the liver fluke to complete its lifecycle, creating highly infected areas where the livestock may congregate to drink.
The implication for livestock farmers is that many will not need to treat while others will need to take action, says Diana Williams of Liverpool University. But the timing of any treatment may be later than expected.
“The only way ensure treatments are necessary and given at the right time is to test,” says Prof Williams.
Sentinels
For several years, regular blood testing has been seen as the best way to detect fluke infection in lambs (or calves). This is because young animals will only show a positive result if they have picked up fluke this season.
“They act as sentinels, telling us if and when they have picked up liver fluke,” says Prof Williams. “By continuing to test at regular intervals through the season, farmers can determine if they need to treat and when.”
Recent diagnostics underline the value of using blood testing.
Last autumn, less than 1% of the animals tested were positive, showing that most farms did not need to treat. This had risen to 10% by mid-November – still a small proportion of farms with the risk of treating too early if following traditional timings.
Rainfall
SRUC vet Heather Stevenson says: “Recent heavy rainfall and relatively mild conditions through into November mean levels may continue to rise during the winter, particularly in areas that were previously dry.”
John Graham-Brown at Liverpool University says: “A negative test does not mean you can sit back and relax. Plan to repeat tests in three to four weeks’ time to make sure you don’t get caught out.
“Sheep are most likely to be seriously affected by acute liver fluke disease in the autumn and early winter, which means they are the priority for testing and are also the best indicator of the presence of liver fluke on the farm.”
Mature
Sheep Veterinary Society vice-president Rebecca Mearns, who is a vet with Biobest, says the laboratory has seen the occasional faeces sample testing positive for fluke eggs this season. “This underlines the need to use the blood test,” she says.
“Most samples received so far this autumn have tested negative, but this does not mean liver fluke isn’t present on the farm, because most fluke inside the animals are not yet mature enough to be detected by a faecal test.”
Philip Skuce from Moredun has some practical advice too. He says: “This is year it is probably easier than most to fence off wet areas that may harbour liver fluke, because on many farms these are small and isolated following the dry summer.
“Feedback from the abattoir on liver rejections is also a very useful source of information and any unexplained deaths are always worth investigating, because a post-mortem examination will check for evidence of fluke in the liver.”
