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Alarming rise in resistant round worms


Grange researcher Orla Keane

Grange researcher Orla Keane

Grange researcher Orla Keane

One of the biggest challenges facing sheep farmers is the alarming rise in stomach worm resistance to the most commonly used doses.

While animal health experts have been warning about the situation for years, the stark reality has only been unveiled by the data now flowing from the Department of Agriculture's Sheep Technology Adoption Programme (STAP).

Samples from 567 farms showed that 48pc of the treatments being used by farmers failed to eliminate stomach worm burdens from the treated animals.

Researchers analysing the data pointed out that there was a risk that some treatments failed because the farmer did not administer enough, or failed to mix the dose properly beforehand, or because an out-of-date product was used. However, Grange researcher Orla Keane said that these were negligible.

"We found that vast majority of treatments, whether they were the white (benzimidazole), yellow (levamisole), or clear (macrocyclic) were effective on one type of roundworm - the nematodirus," said Ms Keane.

"Unfortunately from a farmer's point of view, nematadirus is just one of a group of stomach worms that farmers need to deal with. But it does suggest that the dose was being used correctly in the vast majority of cases. So the obvious conclusion is that the lack of control in relation to the rest of the stomach worms is down to resistance in the parasite," she said.

The findings have massive implications, with sheep farmers spending at least €1m annually on a range of anthelmintic products in an attempt to control round worms. Animal health industry figures suggest that gastro-intestinal worms are costing farmers up to €25m in lost productivity.

And yet, it appears that farmers are not focused on getting to grips with the issue.

"One item on the menu of options that farmers had to chose from in the STAP was to test the levels of parasitic resistance to commonly used anthelmintics. But only half of the farmers that opted for the task of taking a faecal sample before and after dosing managed to carry it out successfully," said Ms Keane.

As a result of the half-hearted approach, the issue is being compounded with every additional ineffective dosing regime carried out at farm level.

"The level of resistance to white doses was over 70pc, while in the yellow and clear treatments, the rates were 44pc and 29pc, respectively. By continuing to dose animals with resistant populations of worms, the farmer is simply killing all the susceptible worms, which means that the ewe or lamb is only shedding resistant ones and multiplying this segment of the population," said Ms Keane.

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