Burnley and Pendle: Wormer Resistance – don’t ignore it

Friday 25 January 2013
Burnley and Pendle: Wormer Resistance – don’t ignore it

The Burnley and Pendle Farmers group recently welcomed independent sheep specialist Lesley Stubbings along to speak about effective strategies to control worms, the increasing resistance issues with anthelmintics and what we as farmers can do to help combat future problems.

The meeting came about following the liver fluke workshop last summer and the questioning looks the speaker got when he mentioned SCOPS (sustainable control of parasites in sheep)!


FACT – worms can reduce growth rates by 50% with NO clinical signs.

Lamb growth rate directly affects feed use efficiency – the quicker lambs grow the more efficiently they use feed and hence the more profitable they are. Reducing the worm burden will improve profitability.

An effective worm control strategy is one which:

Studies have shown that over 90% of lowland farms have resistance issues with BZ (white) drench and almost 50% with LV (yellow) drench as well. It would appear that there is slightly less resistance on hill farms although the problem is still very significant. However many farmers do not know if they have resistance issues on their own farm, and they are more than likely using the same treatments year in and year out with no idea of how effective they actually are.

One simple and easy method of finding out if there is a resistance issue on your farm is to do a drench test on your flock. Take a faecal sample and get it analysed for an egg count (FEC), ideally before the lambs are treated to determine if there is a significant word burden and whether or not they actually need treating. Carry out a second FEC after treatment (LV – after 7 days, BZ and ML – after 14 days). If the reduction in egg count is less than 90% this indicates that there could be resistance issues to the wormer and the worms are not being killed effectively. Resistance will only become physically obvious by reduced lamb performance when the proportion of resistant worms exceeds 50%.

For many years now there have been only 3 categories of drench on the market


Obviously if there is a high level of resistance to one or two of these it means that farmers could have a battle on their hands trying to control worms in the future.

Recently 2 more categories of wormer have been added to the market

The question that Lesley then posed to the group is: should we be using the new groups now or saving them for when the rest have failed?

There was quite a discussion about this with the group and opinion seemed to be divided. In Lesley’s opinion we should be using these groups now but in a selective and controlled way in order to extend the useful life of the existing treatments. For example use the new groups on bought-in sheep whilst they are in quarantine to kill all worms, including any resistant worms that they may be carrying and prevent them being imported to your flock.

The SCOPS website has further detailed and useful information on avoiding the development of resistance in your flock (http://www.scops.org.uk/index.php)

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