Adopting an individual targeted approach to worm control could help maintain both productivity and wormer efficacy, according to Moredun Research Institute’s Fiona Kenyon speaking at NSA Sheep 2010.


“We found from studies conducted over the last four grazing seasons that when whole flocks were treated routinely every four weeks there was a decline in wormer efficacy by about 20%.”

Likewise whole flocks treated strategically three times a year just prior to peak worm numbers saw a drop in efficacy of 7%, compared to a drop in efficacy of only 2% when whole flocks were treated when clinical signs were present or when individuals were treated using the targeted selected strategy.

And although the there was no difference in efficacy decline between the latter two treatments, there was a difference between the two in terms of performance, explained Dr Kenyon.

“Compared to the group that was treated every month, those animals only treated when clinical signs were present saw a decline of 10% in performance. However, in the target selective treatment group, which highlights what individual animals need treating depending on whether they are reaching individual performance targets, there was only a decline in performance of 1%. This clearly highlights that adopting a strategic approach is better.”

And deciding on what method to adopt when worming animals is important, particularly with the development of the new orange wormer. “This is the last chance for some farmers who have multiple worm resistance. It is important to be careful how you treat to prevent resistant to this new drench developing. Consulting your vet is important when developing a worming strategy,” she said.