Anthelmintic Resistance

Anthelmintic resistance

A global threat to livestock farming.

Anthelmintic resistance (AR) is the ability of worms to survive a dose of anthelmintic that would normally be effective. This resistance is heritable and therefore allows resistant worms to pass the trait on to their offspring.

This is a growing problem that we need to combat. At present, there are few new anthelmintics being developed so we must use our existing drugs wisely to slow down the rate of resistance.

This means stopping the regular use of anthelmintics where possible. And when we do use them, we must take care to do so correctly, as anthelmintics become less effective when they’re used incorrectly. Common mistakes include using the right product but in the wrong way, using the wrong product or treating animals that don’t need it.

In addition, pasture is often poorly managed, which further encourages resistance to anthelmintic usage to develop.

How we are helping tackle AR

We use WECs (worm egg counts) to help farmers accurately target the use of anthelmintics and at the same time reduce their costs by not worming unnecessarily.

We can use a WEC to:

  • Accurately diagnose parasites so you can make an informed decision on the best product to use
  • Test parasites’ resistance to different anthelmintic products

How we detect AR

A worm is stated as being resistant if it survives exposure to the standard recommended dose of an anthelmintic and can then pass this resistance on to its offspring (SCOPS 2012).

We can detect AR in livestock using a number of in vitro and in vivo tests. These vary in how expensive, complex and robust they are.

Three of the established tests we provide are:

  • Post-dosing faecal egg counts (drench tests)
  • FECRT (faecal egg count reduction test)
  • LDTs (larval development tests).

The time of year, the worm species present and the test’s specificity and sensitivity can all have an impact on how well AR is detected.

Therefore, it’s important you don’t rely on the results of a single test to determine the degree of AR in the worms on your farm. Tests should be repeated at intervals and as part of an on-going monitoring and health plan for your stock (SCOPS 2012).