Treating liver fluke in sheep

When treating liver fluke in sheep it is important to select a product that will kill the stages of liver fluke that we expect to be in the animal at that time. Stages of liver fluke present at any given time will vary from farm to farm and year to year, so a fixed time treatment protocol is unlikely to give reliably effective results. Different active ingredients are needed at different times of year to target the different stages of fluke that will be present in the animals (see table below). To target these treatments effectively, we need to know when the fluke challenge starts in any field or farm.

Pasture risk refers to the risk of animals being infected with fluke and the stated months are for guidance only as these timings will vary considerably from year to year.

: This is when we would expect the highest level of challenge for new infections of liver fluke, so when we have evidence that the fluke challenge has started, triclabendazole would be the active of choice as this is the only active to kill early immature stages of fluke (from 2 days old) in the liver. However, where triclabendazole resistance has been confirmed on a farm, an alternative active should be used, eg closantel (Flukiver™). As no fluke products are long acting, re-infection will occur if animals are allowed to continue grazing the same area. When pasture challenge is high, it is therefore essential to move animals to a lower risk area or consider housing. This is particularly important if closantel has been used, as closantel will only kill fluke from 5 weeks of age in sheep.
: Once we get into the new year, we would expect the number of metacercariae on pasture to be declining, similarly the risk of new infections to be declining. The liver fluke in the liver should therefore be mostly immature and adults, with fewer early immature fluke present. The actives of choice would therefore be those that target immature and adults. If closantel has been used as an early season treatment, it is advisable to switch to a different active eg nitroxinil (rafoxanide is not a suitable alternative due to the high level of cross resistance between closantel and rafoxanide¹).
: By the summer, we would expect any surviving liver fluke to be adults. A targeted adulticide treatment (albendazole, eg Rycoben, or oxyclosanide) at this time of year will remove any remaining adults and minimise the number of fluke eggs reaching pasture.

When to treat for liver fluke again

As treatments for liver fluke are not long acting, they will only remove the target age range of liver fluke that are present at the time of treatment. Follow up treatments will be necessary if animals continue to graze known fluke risk pasture. However, this should be targeted on evidence of infection.

Post treatment checks

As even a few liver fluke can have a significant impact on the performance of livestock, it is always worth checking that any treatment for fluke has been effective. This can be done using the coproantigen test or composite fluke egg counts following advice from your flock health advisor.