Responsible use of anthelmintics in livestock

From Faecal Egg Count (FEC) to monitoring anthelmintic effectiveness, our advice will help you to use anthelmintics responsibly on farm.

Why is anthelmintic resistance important?

Many farms already have some form of anthelmintic resistance present in their livestock, which can cause major losses in production.

In many areas of England, resistance has been identified (mainly in sheep) to the three main wormer groups (1-BZ, 2-LV and 3-ML) and to the flukicide triclabendazole, due to overuse and incorrect use. In 2018, the first UK case of resistance to the 4-AD wormer group was also reported.

Anthelmintic resistance in worms and liver fluke does not pose a risk to human health.

Monitoring anthelmintic effectiveness

It is important to monitor how effective different anthelmintic groups are on your farm.

The easiest way to check for anthelmintic resistance is to look for the presence of the parasite after treatment, usually by looking for parasite eggs in faeces.

Anthelmintic resistance is only one of the reasons why treatment may appear not to have been effective. Other reasons include:

  • Underdosing
  • Failure to follow the manufacturer’s instructions
  • Rapid reinfection after treatment from highly infective pastures
  • Use of the incorrect product for the target worms

If there is doubt about how well a wormer is working, talk to a registered animal medicines advisor (RAMA) or your vet about doing a wormer or drench test to check for resistance.

Understanding anthelmintic groups

Anthelmintics are categorised into groups according to the parasites against which they are effective, e.g. wormers and flukicides, and the way in which the chemical acts on the parasites.

Understanding these groups is important so that the treatment is targeted to the correct parasite at the relevant stage of its life cycle.

Overuse or poorly targeted use does not just increase the risk of worms developing resistance, it can also be a waste of your time and money.

Targeting treatment

Carrying out a faecal egg count (FEC) before worming can help determine if anthelmintics are necessary. FECs can be done through:

  • The vet
  • A merchant
  • Using a commercial laboratory
  • DIY

FEC can also be used to check that the anthelmintic being used is effective, ensuring you choose the appropriate drug thus helping to maintain drug effectiveness on the farm for longer.

Growth rates

Monitoring growth rates can provide a useful indication of the need for targeted treatment of individual animals. If youngstock are failing to meet growth targets during the grazing season despite good nutrition, a worm burden is a likely cause.

However, remember that the clinical signs of one disease may be the same as for other conditions. A common example of this would be early season lambs with coccidiosis being treated for worms, and vice versa. By routinely treating animals with certain medicines, signs of another disease could be missed.

Care should also be taken to avoid introducing resistance not already present on the farm when buying in animals.

Useful links

Using medicines responsibly

Worm control in sheep

Controlling worms and liver fluke in cattle

Parasite control guide

If you would like to order a hard copy of the following resources, please contact or call 0247 799 0069:

  • Using medicines responsibly 
  • Worm control in sheep
  • Controlling worms and liver fluke in cattle
  • Parasite control guide

Learn more about Sustainable Control of Parasites in Sheep (SCOPS)

Find out more on Control Of Worms Sustainably (COWS)