13 Jul 2021
Open letter to sheep farmers from National Sheep Association, Sheep Veterinary Society and others to help slow concerning upward trend in wormer resistance.
Paul Imrie
Job Title
Image © ulleo / Pixabay
Sheep farmers are being urged to start using the newer group of 4-AD and 5-SI wormers on their flocks now to meet productivity targets and slow wormer resistance.
Bodies including the National Sheep Association, the Sustainable Control of Parasites in Sheep (SCOPS) group, Moredun Research Institute and the Sheep Veterinary Society have penned an open letter to the sheep sector highlighting that despite the presence of anthelmintic resistance on 98% of farms1, 85% still believe their existing wormers work as well as they always have.
Most sheep farmers do not monitor treatment efficacy or growth rates and so are not being alerted to an invisible, but serious, problem.
Vet Matt Colston, ruminant technical consultant at Elanco Animal Health, said many farmers are inadvertently increasing the growth of resistance to group 1, 2 or 3 wormers, while also limiting efficiency and profitability.
He said: “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.
“Integrating the newer group wormers now will also slow the development of resistance to the older group 1, 2 and 3 wormers. This is crucial because once resistance has developed it’s irreversible, and we want as many available worm treatment options as possible, for as long as possible.”
SCOPS advises 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 a quarantine treatment for all incoming sheep and secondly as a one-off treatment for lambs, in the latter part of the grazing season.
Mr Colston added: “To gain the maximum benefit from the treatment for lambs, it’s important that the wormer is given towards the end of the grazing season – as a mid-late season break dose – and when a treatment is deemed necessary through a significant worm egg count. All lambs remaining on the farm should be treated.”
To avoid the risk of resistance to the newer group 4-AD and 5-SI wormers, he emphasised it was very important to not dose and move lambs to cleaner grazing straight away. Lambs should be returned to the same fields for four or five days before being moved.
Vets and farmers can use the Sheep Wormer Checker to inform decisions as to which wormer to use when.
