Lamb growth

Changing worming practices can maximise lamb growth now  
and in the future


There has been a lot of discussion about why we should adopt new ways to worm sheep and, if we don’t, wormer resistance will mean we can’t farm sheep anymore. While on some farms this is true, and fattening lambs is very hard, many farmers will be continuing to fatten lambs and believe resistance isn’t a problem on their farm.

So why should we change how we do things? Often there is a benefit to doing things differently and in this instance, it could allow lambs to grow faster and maximise the benefit from wormers when we use them. In a study comparing growth rates over the summer, lambs that were wormed with an effective wormer grew 2.8kg more than the lambs wormed with a product there was resistance to.1

Worm when there are worms!

Due to the variability of the weather, the worm challenge varies from year to year and from farm to farm. Monitoring with faecal eggs counts might seem another job to do but if it allows you to decide when to worm it could save you time and money. Last summer farms who routinely did worm egg counts often didn’t start worming lambs until the late summer and had to carry on into the autumn.

How to use faecal eggs counts

Ideally, worm egg counts should start in the late spring and continue through the summer. This is because a series of samples provides a better view of worm challenge on your farm than a one-off sample. One of the best ways to use them is to check what wormers are working on your farm by using a simple drench check. This involves taking a poo sample before and after worming to check the number of eggs has decreased by over 90%. If the reduction is less than 90% it doesn’t mean you have resistance but it needs to be investigated, as there can be other causes. However, it does mean your lambs still have worms in them that could be affecting their health and productivity. By finding out the effectiveness of the wormer, you are then able to do something about it quickly if required!

Use wormers strategically

When you know you need to worm the best practice advice is to use white drenches for Nematodirus then swap to one of the clear or  yellows in the summer, then to use the group 4 wormer( Zolvix™) as a break or exit dose in late summer / early autumn.

This mid-late season break dose removes any resistant worms that have built up over the earlier part of the season allowing for a high worm kill. Zolvix can also slow the level of resistance to the older three groups if incorporated into wormer programmes when resistance levels are low2.  Zolvix is also ideal as part of a farm protection quarantine dose to stop resistant worms being bought in and should be used on any incoming animals.

Changing the way we do things isn’t easy but if there is an advantage, it’s worth it. Making sure we use our time to the maximum benefit is one of the reason why adopting new worming strategies is a good plan and ensures good productivity now and can help sustain it in the future.



1.      IA Sutherland et al The production costs of anthelmintic resistance in sheep managed within a monthly preventative drench program, AgResearch Ltd, The Hopkin Institute and Novartis Animal Health

2.      DM Leathwick and BC Hosking Managing anthelmintic resistance: Modelling strategic use of a new anthelmintic class to slow the development of resistance to existing classes, New Zealand Veterinary Journal 57(4), 203-207, 2009


For further information call Elanco Animal Health on +44 (0)1256 353131 or write to Elanco Animal Health, Lilly House, Priestley Road, Basingstoke, Hampshire, RG24 9NL. Zolvix™ 25mg/ml oral solution is a broad spectrum anthelmintic for the treatment and control of gastro-intestinal nematode infections and associated diseases in sheep including lambs, hoggets, breeding rams and ewes. Legal category: POM-VPS. Information regarding the side effects, precautions, warnings and contraindications can be found in product packaging and leaflets; further information can also be found in the Summary of Product Characteristics. Advice should be sought from the medicine prescriber prior to use. Zolvix, Elanco and the diagonal bar logo are trademarks of Elanco or its affiliates. Use medicines responsibly (www.noah.co.uk/responsible). © 2019 Elanco and its affiliates. PM-UK-19-0472. Date of preparation June 2019.

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