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Welsh Sheep Study Shows Worrying Resistance to New Anthelmintics

22 May 2015

WALES – A Welsh farm survey has offered a “depressing” update on the developing anthelmintic resistance issue, showing higher resistance across all three groups.

Wormer efficacy has diminished over the last nine years across groups one, two and three – white, yellow and clear, preliminary results from a study of 28 welsh sheep operations have shown.

The figures offer fresh insight on Welsh resistance to group 3, which include the clear drenches Ivermectin and Moxidectin. Moxidectin was classed as a distinct fourth group by the study.

Only one farm showed no resistance from faecel egg count tests. 

The results are part of a Hybu Cig Cymru (Meat Promotion Wales) study of 45 welsh farms looking into round worms and fluke, testing for BZ (group 1) LV (group 2) ML (group 3) Moxidectin separately and triclabendazole resistance for fluke.

The assessment was to update understanding following the Worm Watch Project in 2006 which showed resistance to group one and two.

Addressing farmers at NSA Wales this week, Lynfa Davies, technical development executive at HCC, said: “Unfortunately there has been an increase of resistance in Wales. While the results may look a bit depressing, its useful to be assessed so you can react and change.”

It helps if farmers know their resistance levels - Eurion Thomas, Techion

However, the timing of the farm assessments late in the year mean spring and summer worms like Nematodirus, Telodorsagia and Haeronchus have been missed out. The findings are for winter parasite Trichostrongylus.

Eurion Thomas, European operations manager at Techion told the NSA seminar that the study had its limitations but urged farmers to keep the group 3 anthelmintics working.

Summarising the study, he said: “The Trichostrongylus worm was very dominant in the study and survived in most cases.

“We don’t know the situation early on in the year, the next step would be to look at more farms in summer."

He added that the important message for farmers was “all is not lost” and that there were alternative management approaches to take.

“The biggest thing is that farmers know their resistance status – if you don’t know, you can’t tackle the issue.”

He identified Moxidectin as a stand-out drug in the current situation, highlighting its other use in combatting sheep scab.

“Long acting moxidectin is excellent but there is a tendency to overuse it,” said Mr Thomas. “Its really important to keep this working as its one of the best wormers we have.”

Responding to the study, Veterinarian Laura Higham, a consultant with FAI Farms said: “The study found high percentages of farms with resistance to groups one and two anthelmintics, the white and yellow drenches, but with concerning emergence of farms with triple resistance to groups one, two and three.

“These farms showed resistance to group three clear drenches, possibly due to the wide use of these products to prevent and treat sheep scab.”

Headline image courtesy of Sira Studios

Michael Priestley

Michael Priestley
News Team - Editor

Mainly production and market stories on ruminants sector. Works closely with sustainability consultants at FAI Farms.

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