Adopting an individual targeted approach to worm control could help maintain both productivity and wormer efficacy, according to Moredun Research Institute’s Fiona Kenyon.
“We found from studies conducted over the past 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 as a result of clinical signs or when individuals were treated using a targeted selection strategy.
And although 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 which 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 what worming method to adopt 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.
This is increasingly important with resistance to all three traditional drench groups found increasingly across the UK, said Mike Taylor of the Food and Environmental Research Agency.
“The main danger is from under-dosing sheep and from overuse of products when there is no need to drench. The introduction of a new class of wormers will help reduce the resistance pressure on the existing drugs and new treatments can be used very effectively in quarantine procedures and to give a break treatment during the season.”
And while reports of flukicide resistance are also increasing Mr Taylor said it was unlikely there were that many cases where true resistance had developed. “In many cases there may well be treatment failure, but this could be due to all manner of reasons, such as underdosing or excessively damaged livers.”