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Stackyard News Jul 06

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Control Worm Build-up with Careful Management

With pasture worm burdens building-up rapidly across the country over the past few weeks, good management will be essential this summer to maintain post-weaning lamb growth rates and avoid delays to finishing.  Worming programmes will, however, need to be particularly well-planned and managed to combat the growing problem of anthelmintic resistance.

© photo courtesy


This is the timely warning from the English Beef and Lamb Executive (EBLEX), following testing showing resistance to benzimidazole white drenches now affects more than 80% of lowland flocks, with some farms seeing resistance to all three main classes of wormer.

Combined with post-weaning stress, high July and August worm burdens can more than halve lamb growth rates from at least 125 g/day to as little as 50 g/day, seriously compromising the capacity for lambs to be finished early and economically enough off grass for the best autumn returns. What is more, the wet early season and current warm, moist conditions means worms are likely to prove especially damaging this season.

The rise in anthlemintic resistant worms means English flocks can easily make this situation worse by failing to plan and manage their worming as well as possible, increasing their immediate costs for little performance gain and making future control even more problematic.

To prevent lamb performance being compromised while reducing problems from anthelmintic resistance in line with SCOPS advice, EBLEX recommends strategies that reduce the frequency and maximise the effectiveness of anthelmintics. In particular, it advocates:

  • Making sure all stock receive sufficient anthelmintic by drenching animals at the correct rate for the heaviest in the group, checking the accuracy of worming equipment and delivering the entire dose over the back of the tongue;
  • Avoiding rigid routine worming programmes which usually result in over-use of anthelmintics, increasing both costs and the risk of resistance development;
  • Worming only when necessary, using Faecal Egg Counts (FECs) to monitor levels of actual animal infestation over the season;
  • Checking the effectiveness of each anthelmintic treatment with routine FECs a set number of days after worming;
  • Weaning stock onto lower worm risk pastures in mid-season as part of a planned programme of grazing management based on pasture categorisation by risk level;
  • Keeping drenched stock on dirty pasture for a few days or leaving 10-20% of animals untreated to guard against populating clean or low risk grazing with resistant worms;
  • Choosing the most appropriate product for the target worm wherever treatment is needed, avoiding combined products, and using anthelmintics from different activity groups in sequence to reduce the selection pressure for resistance; and,
  • Monitoring current worming practice with a simple checklist as the basis for future improvement.
A useful worming checklist and practical guidance on better returns from planned worm control is available in the latest EBLEX Lamb Action for Profit Factsheet at

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