Sheep farmers are being reminded to incorporate a group 4 (orange) wormer into their control strategies, to prevent resistance building and maintain production efficiency this season.

According to Matt Colston, vet at Elanco Animal Health, wormer resistance is a growing, yet invisible problem, with data showing that 94% of farms are resistant to white wormers, 68% resistant to yellow wormers, 51% resistant to ivermectin and 19% resistant to moxidectin.

He said that monitoring of growth rates and routine testing will help alert farmers to potential resistance issues, although emphasises that it is crucial not to wait until there is an identified problem before strategically introducing a newer wormer active.

“Repeated use of the same wormer groups will speed up the rate that resistance develops and once this happens, it cannot be reversed. Introducing a newer group 4 wormer at strategic points within worming programmes now will therefore pay dividends.

“It will help slow down the development of resistance to the older wormers, deeming them more effective for longer, and clear out any resistant worms that could be compromising lamb growth and performance,” he explains.

He recommended swapping one dose of an older group 1, 2 or 3 wormer, to Zolvix™ for lambs in the mid-late grazing season.

“This should deliver visible improvements in lamb performance, by removing any resistant worms left from previous treatments.

“On top of one annual dose for lambs, Zolvix should also be used as a quarantine treatment for any incoming sheep, to prevent resistance being brought onto the farm,” he advised.

Mr Colston said farmers should not worm sheep and move them to clean pastures straight away.

"Sheep should be housed or returned to the same fields for four to five days before moving. This avoids taking any resistant worms that have survived treatments onto clean pasture.

“Farmers should also undertake a post-dosing faecal egg count, also known as a drench test, whenever a wormer is given. This can quickly provide an indicator of wormer efficacy and determine whether further treatment is needed,” he adds.

The government’s new Animal Health and Welfare Pathway is set to offer support for wormer efficacy testing, providing the ideal opportunity for farmers to work with their vets and establish a sustainable worming programme.

For further advice on which wormer to use and when, head to the Sheep Wormer Checker