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12 July 2021

In an open letter to the sheep industry, Sheep Veterinary Society, National Sheep Assiocation, the Sustainable Control of Parasites in Sheep group (SCOPS), and the Moredun Research Institute, have this week highlighted that despite the presence of anthelmintic resistance on 98% of farms, 85% of farmers still believe that the wormers they use are working as well as they always had.

This is largely down to the fact that the majority of sheep farmers do not monitor treatment efficacy or growth rates, and they are therefore not being alerted to what is essentially an invisible, yet highly consequential, problem.

According to vet Matt Colston, ruminant technical consultant at Elanco Animal Health, this is a dangerous strategy, and many farmers are inadvertently increasing the growth of resistance to group 1,2 or 3 wormers, while also limiting efficiency and profitability. He says: “Because most farmers can’t physically see the reduction in lamb performance, they’re often reluctant to adopt new management practices. Yet we know, swapping a dose of an older group 1,2 or 3 wormer to a group 4-AD (orange) or group 5-SI (purple) wormer in the latter part of the grazing season, will give a visible improvement in performance in most cases, as worms left by previous treatments are removed.”

SCOPS advises that one of the two newer groups to be used on all sheep farms at two points in their worm control plan. Firstly, as part of their quarantine treatments for all incoming sheep, and secondly as a one-off treatment for lambs, in the latter part of the grazing season.

To help support the transition to a more sustainable worm control programme, producers are encouraged to use the Sheep Wormer Checker, available here, to inform decisions as to which wormer to use when. Further information on choice of anthelmintic is available at the SCOPS website.

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