Understanding Liver Fluke in Sheep Flocks
TECHNICAL BOX There are currently no validated field tests for detecting liver fluke resistance in live animals but faecal egg count reduction testing (FECRT) can be indicative of resistance. A FECRT can only be done when adult liver fluke are expected to be present. Individual faecal samples are collected from the same 10 animals pre-treatment and three weeks post-treatment with a flukicide. Samples are sent to the laboratory for a faecal egg count and a reduction in egg counts of 90-95% imply a successful treatment. A coproantigen reduction test can be similarly performed on samples from 10 animals pre-treatment and two weeks post-treatment with a flukicide. Mean coproantigen positivity should fall by 90% if treatment is successful. Treatment success should be evaluated against the expected life stage of the liver fluke present and the efficacy of the product for that stage. Triclabendazole efficacy can be assessed when late immature or adults are present, whereas other flukicides should be tested at times when only adults are expected. If possible, confirmation of suspected resistance by dose and slaughter trials can be undertaken. Minimising the risk of liver fluke infection Not all approaches to minimising liver fluke infection risk will be practical or cost-effective on all farms, but the seriousness of liver fluke infections means they all warrant consideration, and action where feasible. To reduce the risks of animals becoming infected with liver fluke there are several options to consider: • Improve the drainage of any wet fields to reduce the habitat of the snail host that transmit liver fluke. Consider fencing off very wet areas which cannot be drained. Alternatively, risky fields could be used for silage. The risk of infection by liver fluke parasites in ensiled grass is dramatically reduced if silage is properly preserved. • Plan grazing rotations to avoid placing animals on the wettest fields during the highest risk periods (late summer through to early winter). • Make use of fluke risk forecasts and FEC tests to inform grazing rotation and treatment plans, as the seasonality of liver fluke risk is highly dependent on climate and can vary from year-to-year. • After lambing, move ewes and lambs onto the driest fields to minimise the risk of acute disease in growing lambs.
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