Anthelmintic resistance: a New Zealand perspective

The general belief in New Zealand is that their anthelmintic resistance problem is far greater than the UK’s, and if the UK acts now to manage resistance we may avoid the problems faced by many New Zealand farmers.

The reasons behind the New Zealand resistance situation are many and varied. Some farmers believe that government agricultural subsidies helped fund the overuse of some anthelmintic compounds that were considered to be effective at the time.

When these subsidies were withdrawn in the 1980s, agriculture went through a difficult period of restructuring, and it was at this point that vets and farmers started to realise there was a significant problem with failing anthelmintics. Whatever the reason, it is clear that many sheep farmers were unable to continue to farm profitably due to failing wormers.

Existing classes of drench were reformulated into double and triple multi-drenches, and introduced to the market as a solution to these problems. However, these products are failing as multiple drug resistance becomes more common.

Many farmers say advances in wormer technology have been essential for the New Zealand sheep industry, most notably the introduction of a fourth generation of anthelmintic, known as the 4-AD or orange drench.

The compound works on a specific nerve receptor, so has a unique mode of action and kills all resistant worms, including those resistant to multiple actives. In New Zealand its use has partly replaced double and triple dual active drenches, and its integration into worming programmes is in turn helping prolong the life of such products.

Farmers in New Zealand do feel they are fortunate to still have good options for the control of worms and an opportunity to manage anthelmintic resistance before it runs out of control.

The differences between New Zealand and UK agriculture are great, but ideas about healthcare, lamb marketing, welfare and parasite control can be exchanged to enhance the farming industries of both countries.

Sarah Grantham is a Novartis Animal Health and National Federation of Young Farmers Clubs scholar

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