Anyone who has been to any of my talks on parasites or FECPAK training events may remember that even though wormer resistance is rife in most roundworm species in the UK all wormer groups seemed to be effective against Nematodirus which is the nasty worm we normally associate with disease in young lambs in the spring. Our advice would have been that even though the white drench group (1 BZ) has widesperad resistance to most worms it could still be used against Nematodirus and is actually one of the best wormers to tackle this nasty worm due to its mode of action.
Unfortuantely this has now all changed as a few weeks ago the first case of white drench resistance was confirmed on a farm in Cumbria. It looks as if we have to be a bit more careful now with overdependence on white drenches in the spring period to cover Nematodirus. In years where Nematodirus risk is lower (such as this season in most parts of the country) we probably need to consider other wormer groups and keep the white drenches for when we really need them in season when Nematodirus incidence is higher and poses more risk.
In reality it was a mystery why we hadnt seen resistance with this species before as it the species with the biggest issues in New Zealand. There are probably many farms out there that may have some level of resistance - its just we havent looked yet. Another reminder for us all to be vigilant with wormer use and that we take steps to try and help keep our anthelmintics working for longer.
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