18 April 1997

Resistance forces a rethink

SHEEP producers should rethink their worming programme as resistance rises, summers become drier and new products offering prolonged control become available.

So says ADAS sheep specialist Lesley Stubbings, who says that producers should reconsider their programmes and product choice.

"Resistance to wormers is an increasing concern which needs to be addressed. Alternating drug groups year on year will minimise the risk of resistance."

Dry summers usually mean theres little worm activity, says Ms Stubbings. "It is probably worth checking dung samples before deciding when to start worming. Your vet or local vet investigation centre should be able to do these, and results will be back quickly."

And where producers choose to use the new generation of wormers such as Cydectin, which offer prolonged control, she warns that a change in approach will be needed maximise their benefits.

"These wormers have a double benefit – they kill all worms and larvae within sheep, and lower levels on pasture. They also offer protection for six weeks, and producers should not be tempted to worm before that interval is up even if lambs start to scour.

"Ninety-nine times out of 100 producers will blame worms if lambs start to do less well or scour. Its not necessarily the wormer to blame; for instance, it could be a change in grass availability."

When using products with a three-week gap between treatments do so properly, she says. Weigh the largest sheep in the group and dose at that level.

Dont cut rates – and check calibration of your dosing gun. And dont be tempted to reduce the gap between treatments to less than three weeks."