Winter Fluke Housing Treatment Article Series – Part 2

Chris Gregory MRCVS, Molecare Farm Vets

Housing offers a perfect opportunity to break the pasture-based fluke lifecycle. The following article builds on last month’s discussion around assessing the risk of fluke infestation on your farm, highlighting the practicalities of timing treatments and selecting an appropriate active ingredient.

Treatment Options & Timing

At housing, an animal could be harbouring multiple stages of the fluke parasite depending on pasture risk and seasonal exposure ranging from:

1. Fresh fluke cysts ingested off pasture – effectively ‘day 0’ of infestation
2. Early Immatures – Over ~8 weeks, immature fluke migrate from the gut across the liver causing damage as they go
3. Late Immatures – Over ~8 weeks, immature fluke migrate from the gut across the liver causing damage as they go
4. Adult fluke in the liver (gall bladder and bile ducts) – ~10-12 weeks after ingesting the cyst NB. Only at this point will fluke eggs be identifiable in dung samples.

Once housed there are no more fluke cysts ingested, allowing all current immature stages to catch-up to the adult stages. Theoretically, after 10-12 weeks (mid-late housing period) only adult stages would exist in the animals.

Looking at the table below, different products kill fluke stages from 2 weeks post-ingestion all the way through to adults at 10-12 weeks or more post-ingestion NB. None of the products kill fluke less than 2 weeks old. This presents a range of possibilities with respect to timing treatments.

Possible options:

1. Treat at housing

Systems geared around minimal handling e.g. housed forward stores or fat cattle close to finishing that will not go back out to grazing. In this case a housing dose reduces the stress/growth check of additional gatherings for treatment(s). Although there will be some stages of fluke untreated, most of the grazing burden is cleared and impact on growth rate reduced. Commonly a combination product to eliminate worm burdens will be used with this strategy to maximise the efficiency of the single dose at housing approach.

2. Delay treatment

Systems capable of multiple handlings and animals less prone to growth checks (e.g. suckler cows). A single treatment  could be delayed until a product has its maximum effect.

e.g. Triclabendazole – delay treatment until 3 weeks after housing

e.g. Clorsulon/Closantel – delay treatment until 8 weeks after housing

3. Additional pre-turnout treatment

Where there is any suspicion of fluke stages left untreated, an additional late housing dose could be carried out. Especially if the cattle are to return to grazing the following spring.

e.g. Cattle dosed at housing for convenience may still have a residual fluke burden.

e.g. Systems, where cattle out-winter or have limited access to grazing, may re-infect after initial treatment as none of the fluke products have persistency.

Any cattle that carry a residual adult fluke burden through housing will begin to contaminate pasture immediately after they are turned out again.