Triclabendazole can kill even very young immature liver fluke. As a result, it is a useful product when treating incoming sheep.
Unfortunately, resistance to this product has been reported. Despite this, in most cases, it is still very effective and should be included in most quarantine treatments from late summer to early winter.
However, any resistant fluke would survive treatment with this product. It should be used in conjunction with a second fluke treatment at a later date, to guard against these resistant fluke being brought into your flock.
When to use
Use triclabendazole from August to January as a quarantine treatment.
Use a second fluke product in addition (not at the same time).
Discuss timings of treatments with your farm vet.