What role do sentinel lambs play in liver fluke control?

Testing young lambs through their first grazing season is becoming an increasingly popular technique to monitor fluke risk, say animal health experts.

Focusing on these “sentinel” lambs for signs of liver fluke infection can save time, effort and money by informing flockmasters of the disease challenge.

In the face of increasing resistance to the widely used active triclabendazole, they have called for vigilance from farmers before the 2025 grazing season, urging them to “test, don’t guess”.

Farmers Weekly asks sheep vet Phillipa Page of Flock Health how to run a sentinel lamb system.

See also: Liver fluke: Symptoms, diagnosis, treatment and prevention

How do sentinels help in finding fluke?

Testing sentinel lambs will indicate their exposure to liver fluke in the current year. This can be done by the vet using a blood sample, or by the farmer using the new lateral flow test for fluke.

Detectable antibodies are present in their blood from two weeks after exposure.

Where should I put the sentinel lambs?

This approach only indicates exposure from pasture that lambs have grazed, so to determine the need to treat adult ewes, a group of 10 sentinel lambs (ewe lambs or castrated stores) should graze with the main flock and be routinely tested.

Home-bred animals are most suitable. Bought-in lambs may indicate infection from their home farm, and fluke antibodies can remain detectable for a prolonged period.

For the same reason, testing ewes may also show antibodies arising from infection in the previous year.

How often should I test?

Typically, testing should start from late summer and continue into autumn and winter.

A one-off negative test in late summer indicates that exposure to fluke has not yet occurred, but tests need repeating as the season progresses.

Once positive results start to be seen, treatment is necessary. This will be accurately timed, and the correct drug can be selected.

Changes in weather and seasonality mean hard and fast rules are difficult to prescribe.

But a general rule of thumb is that lambs should be tested once a month from late summer through to winter – typically from August to December.

Use of the test and the results should be discussed with the farm vet as part of a flock health plan.

Which test should be done?

The lateral flow test will pick up the antibodies and can be done by the farmer when the flock has been gathered. Results are available immediately, so treatment can be decided on the spot.

This test cannot be used to check for anything else. However, the vet can visit and take blood samples to check for liver fluke antibodies and other issues such as trace element deficiency.

Advice on sustainable liver fluke control was given at a recent webinar by the National Animal Disease Information Service.