This week’s management notes touched on an issue which continues to raise its head – incorrect products being administered for liver fluke.
Reports from vets and farmers point to significant numbers of farmers treating ewes and lambs at present for liver fluke.
The objective is correct for farmers with a tradition of substantial problems.
However, many of the treatments being administered are close to worthless at this stage of the year, as products selected target the mature stages of the liver fluke life cycle when the greatest threat in October and November is from the early immature and immature stages.
Acute liver fluke
Acute liver fluke caused by the ingestion of large numbers of early immature larvae poses the greatest risk from September through to December.
This will transition to sub-acute fluke over the immediate months ahead and it is commonplace for acute fluke and subacute fluke to present a challenge at the same time.
Therefore, it is important during this timeframe that products are used that at least cover immature and mature fluke stages of the life cycle.
Table 1 details the active classes of flukicides available as a standalone product and the stage of liver fluke each targets.
Trichlabendazole products are the obvious choice, as they cover all stages, but some producers have resistance issues, so caution may need to be exercised.
Using products that target only mature liver fluke stages during this timeframe leaves sheep heavily exposed.
Closantel and rafoxanide products target mature and immature flukicide, while nitroxynil is the active ingredient in Trodax, which was taken off the market and has been replaced by Fascionix 34%, which is a similar product.
The use of oxyclozanide-based products is generally advised against for fluke on the premise that it is the only ingredient class which has been shown to be effective against rumen fluke and, therefore, there is an appetite at industry level to protect its use for this cause.
Accidental or convenient treatment
In many cases at this time of year, sheep are incorrectly treated for worms and fluke as a consequence of combination worm and flukicide products being used.
This is due to a number of combination products which are common among farmers containing a flukicide that only targets mature liver fluke.
This approach is also increasing the rate at which anthelmintic resistance is developing in worms, with no need to treat healthy mature sheep without a demonstrated need (for example, haemonchus contortus or barbers pole worm).