Wednesday, 20 June 2018

How farmers can limit anthelmintic resistance


Nerys Wright, Knowledge Exchange Manager for AHDB Beef & Lamb talks about the recent confirmation of the first case of resistance to Monepantel (Zolvix™) in the UK and the importance of ensuring that best practice is followed when administering wormers to sheep.

We have been using anthelmintics (wormers) for decades for worm control on our sheep farms. However, the worms are evolving and becoming capable of surviving a wormer dose that previously would have eradicated them. Over a period of time, these anthelmintic-resistant worms multiply and can cause poor lamb growth rates and sometimes lamb deaths.

Recent news confirms that Montepantel, a recent addition to the family of wormers, now has parasites that are resistant to it. It is therefore a timely reminder for farmers about the importance of following best practice advice.

Prior to 2010, there were three main types of wormers 1-BZ, 2-LV and 3-ML groups, all with a different mechanism of killing the worms. The introduction of group 4-AD in 2010 closely followed by 5-SI in 2012 provided the sheep industry with two new groups that would firstly prolong the life of the other groups and also provide new options for farms with resistance issues to the older three groups. It is when farmers rely almost exclusively on one wormer group combined with moving sheep to low challenge pasture (ground that has had any recent break from young lambs or lactating ewes) that the selection pressure leads to worms developing resistance quicker.

We support an industry body called Sustainable Control of Parasites in Sheep (SCOPS) that represents the interests of the sheep industry. It recognises that, left unchecked, anthelmintic resistance is one of the biggest challenges to the future health and profitability of the UK sheep industry.



The SCOPS website gives some great advice on how to reduce anthelmintic resistance:

  •  Wormer groups 4-AD and 5-SI should be incorporated into worm control programmes on all sheep farms, their real value is in prolonging the life of the older 1-BZ, 2-LV and 3-ML groups
     
  •  A Group 4-AD or 5-SI wormer should ONLY be used as a quarantine drench on incoming animals and during mid/late season as a ‘one off’ annual drench for lambs. Use at other times should only be done under veterinary direction and only if the full anthelmintic resistance status of the farm is known.
     
  • Effectiveness of products used should be monitored carefully. Speak to your vet or a suitably qualified person (SQP) about how you can do this
  • If you are moving sheep to low challenge pasture after treatment, they must be left on dirty pasture for four to five days prior to moving or you should leave 10 per cent untreated. This is because if you dose and immediately move to a low challenge field, the only worms that will be taken are resistant ones (within the sheep). They will not have any breeding competition from a susceptible worm population. Turning them back to the ‘dirty’ pasture to pick up some susceptible worms or leaving 10 per cent of animals untreated will allow for the resistant worms to mix with the susceptible worms and the speed at which resistance will develop can be reduced. 


It is vital farmers treat their flock correctly with wormers. Best practice must always be followed:
  • Ensure the correct dose rate – dose to the heaviest in the group
  • Calibrate the gun and administer correctly, over the back of the tongue or into correct site if using an injection
  • Know how well wormers are working on your farm and only administer a wormer when it is necessary. 
For more information, please read the BRP manual Worm control in sheep for Better Returns and visit the SCOPS website