Blanket treatment of ewes with anthelmintics (wormers) at lambing does not lower subsequent worm burdens in lambs, new research has found.

The research by UK government’s Animal Plant and Health Agency (APHA) was carried out on 16 commercial farms over three years and tested the effectiveness of blanket treatment of ewes with both long and short acting anthelmintics at lambing.

The research found that the faecal egg count in lambs at 10 to 16 weeks of age on farms, where ewes were treated with either short- or long-acting wormers, were not lower than the egg counts of lambs on farms where ewes were not treated.

Worm contamination

Anthelmintic treatment of ewes at lambing is a widely used practice on sheep farms to reduce subsequent worm contamination of grassland.

“We could not demonstrate any clear benefit in terms of worm infection levels in lambs as a result of worming ewes on the farms studied,” Jane Learmount from APHA said.

The Sustainable Control of Parasites in Sheep (SCOPS) guidelines have previously recommended that sheep farmers leave 10% to 20% of ewes untreated, so that the worms shed on grassland are not resistant to the anthelmintics used on the rest of the flock.

However, researchers state that this latest study provides further evidence of the benefit of an even more targeted use of wormers in ewes.

Ideal condition

“We can confidently tell farmers that they only need to treat the proportion of the flock that is below ideal condition, or immature shearlings or ewe lambs,” Lesley Stubbings from SCOPS said.

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