Half of lamb wormers ‘ineffective’

Almost half of all anthelmintic treatments given to lambs are considered ineffective, according to a study by Teagasc.

The result highlights the importance of testing the efficacy of the wormer before use, with the study noting that tests known as ‘drench tests’ should be carried out on the product before use.

It was also said that worm resistance to at least one class of wormer is a reality on many farms, and that multiple drug resistance is a serious threat.

The study added: “Grazing sheep are naturally exposed to parasitic roundworms that live in the gut and infection can result in chronic disease, ill thrift and occasionally death.

However, an unavoidable result of continuous use of wormers is the development of drug-resistant worms.

‘Drench testing a requirement’

Under the Sheep Technology Adoption Programme (STAP), which ran from 2013 to 2015, a series of tasks had to be carried out each year in return for a monetary reward. Among these tasks was the requirement to drench test.

The participants had to test either benzimadazole (white group), levamisole (yellow group) or macrocyclic lactone (clear group), depending on which they were using.

Some 4,211 drench tests were undertaken by farmers during the three years of the programme.

The study defined “ineffective” as killing 95% or less of the worm population, which occurred in 49% of cases.

“Ivermectin resistance was confirmed in two out of four farms that were previously declared as having suspected resistance. The species of roundworm found to be resistant was the brown stomach worm.

“The development of parasites resistant to a number of drugs is concerning,” the study said.

‘Faecal egg counts a vital tool’

By taking a faecal egg count (FEC) – which involves counting the number of worm eggs present in dung – it is possible to get an indication of the number of adult worms in the gut of sheep, according to Teagasc’s Frank Hynes.

Any farmer wishing to carry out this test must contact an appropriate laboratory and request a sampling pack, with a list of approved laboratories for testing available here.

When taking faecal samples, it is advised to place 15 lambs in a pen and gently move them about until they defecate, taking the samples “immediately”, Hynes said.

The test should coincide with peak infection period, which usually occurs from June to September.

“The samples should be taken early in the week. This avoids the samples being held in the post over the weekend.”

Worms tested for include strongyle; nematodirus spp.; coccidial oocysts; threadworms; tapeworms; and lungworms.

If there is a FEC of greater than 500 eggs per gram (EPG), lambs should be dosed immediately. If there is less than 500 EPG, dosing does not have to be immediate but retesting in the near future may be advisable.

If there are between 400 EPG to 500EPG, dosing in one to two weeks’ time is recommended.

FECs can be used to:
  • Help determine whether animals need to be dosed or not;
  • Help better timing of dosing;
  • Test the efficacy of the dose (drench test or faecal egg count reduction test);
  • Reduce the number of doses where anthelmintics are used excessively;
  • Obtain information on the level of worm contamination going onto pasture.