A report of nematodes being found in Dutch sheep that are resistant to the 4-AD group of anthelmintics highlights the danger of not properly rotating wormers.

But what is concerning Dutch experts is that the product in question (monepantel) had only been on the market since 2011 and they believe it could be the first case of haemonchus contortus (barber’s pole worm) resistance to the active.

The UK cross-industry group Sustainable Control of Parasites in Sheep (Scops) is, therefore, urging vets and farmers to integrate 4-AD and 5-SI wormer classes into their worm control programmes.

See also: Vet viewpoint: Sheep tapeworm can reach six metres long

While the full details are not yet available, Scops believes this situation has arisen because the farm relied on the 4-AD product because of resistance to all the other classes available.

This comes as a timely warning to the UK, says Peter Baber, Scops chairman and sheep farmer.

“This is exactly the situation Scops predicted would occur if we do not integrate the new groups into worm control strategies before the older products become ineffective.

“There are still a large number of UK farms where one or more of the three older groups remain effective. If we carefully integrate the 4-AD and 5-SI products into worm control programmes now, it will extend the useful life of all groups.

“The Dutch example serves to illustrate the folly of us leaving them until they are the only option.”

Monepantel, manufactured by Novartis Animal Health, has a unique mode of action compared with all other available anthelmintics. It causes paralysis in worms by binding to a specific receptor found only in nematodes (roundworms), says the firm.