The very limited number of flukicides available to treat cattle and sheep means it is essential for farmers and their vets to fully understand their product choices.
This is according to new advice by animal welfare groups Sustainable Control of Parasites in Sheep (SCOPS) and Control of Worms Sustainably (COWS).
They say the key to choosing the right product is understanding the differences between the actives available and the age of liver fluke parasites that needs to be killed.
This will not only reduce the risk of repeated/overuse of the same flukicide, but also ensure the best outcome for the sheep or cattle treated.
Lesley Stubbings, an independent consultant speaking on behalf of SCOPS, explains that, in essence, there are three groups of flukicides.
"Triclabendazole is the only one to kill immature liver fluke, from two days in sheep and two weeks in cattle," she says.
"Closantel and nitroxynil kill liver fluke down to about five weeks of age, but nitroxynil can only be used in the UK if imported by vets under a VMD special import certificate.
"Albendazole and oxyclozanide, plus clursulon for cattle and rafoxanide for sheep, kill only adult liver fluke.”
Resistance to triclabendazole on some farms means they now rely on closantel to control immature fluke, which normally requires two treatments six to seven weeks apart, according to SCOPS and COWS.
They say it is important farmers, vets and advisers realise – due to restrictions on nitroxynil – there is no alternative to closantel currently available.
Rafoxanide, which is only licenced for sheep in the UK, is not an alternative because both closantel and rafoxanide are salicylanilide molecules and have very similar chemical structure and mode of action.
Ms Stubbing concludes: “SCOPS and COWS are very concerned people are mistakenly thinking that by using rafoxanide they are protecting closantel. The reality is quite the opposite.
"Experts working with SCOPS and COWS agree there is evidence of cross-resistance between rafoxanide and closantel from both field and laboratory studies.
"[There is] no evidence to suggest using them interchangeably will reduce the selection pressure for resistance to closantel.”
