Farm Ireland

Monday 19 February 2018

Ivermectin resistance confirmed on sheep farms

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Louise Hogan

Louise Hogan

FARMERS have been urged to carry out faecal egg counts to assess worm burdens and look at wormer efficacy, as ivermectin resistance has now been identified on sheep farms.

Teagasc's Barbara Good warned multiple drug resistance has also been confirmed in Irish flocks.

Dr Good said the examination of data from the STAP figures of about 1400 farms identified treatment failure in 49pc of flocks.

Treatment failure of the white drench for worms was found mid- season in 68pc of flocks.

The parasite expert said it also found treatment failure of yellow drenches was found in 48pc of flocks and for ivermectin in 38pc.

"We can say with reasonable confidence that a lot of that is to do with anthelmintic resistance as opposed to dosing issues as such," she said, adding the STAP results mirrored work carried out by Teagasc.

However, she urged farmers to ensure they were not contributing to treatment failures by giving the incorrect dose or not checking the calibration of the dosing gun.

"The fact is your choices are more limited if you have resistance - we do have two prescription only medicines on the market which gives farmers more choice. All hope is not lost I suppose."

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Dr Good pointed out the white drench should still be used as the first dose for the early gut worm, nematodiris.

"It is important that farmers actually test their own flocks," she said.

"The drench test is a simple test to do. It is effective - it gives you information on whether your doses are working.

She said knowing the flock faecal egg count will give the farmer the knowledge to make the decision on whether they should be dosing or not.

Dr Good said another study looked at some farms where there were suspicions of ivermectin resistance. It found resistance in two of the four farms to the medium brown stomach worm.

"That is new knowledge that we actually have ivermectin resistance out there," she said.

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