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Worms In Sheep: Choosing A Product

16 March 2017

There are more than 50 sheep worming products on the market making it impossible to remember them all.  Happily you don’t have to as knowing a few facts will go a long way in helping you choose a product.

Wormer Groups

All the wormers can be divided into 5 groups based on the chemical (active ingredient) they contain.  The group they belong to should be indicated on the box or the enclosed information.  Look out for the following codes:  1BZ, 2LV, 3ML, 4AD and 5SI.  Group 1 and 2 wormers have been around since the 60s and 70s and are no longer completely effective on many farms.  See for a list of wormers by group.

Long Acting Wormers

Only 3ML products containing moxidectin (Cydectin, Zermex) have any long acting activity against sheep worms.  This varies depending on the type of worm and the route of administration.  Moxidectin drenches have no persistence against Nematodirus battus or the black scour worm (Trichostrongylus sp.) which is most common in late autumn/early winter.  Moxidectin injections have reduced persistence against the black scour worm and are not licensed as a treatment for Nematodirus battus.  Don’t get caught out in winter or spring.  All the 1BZ, 2LV, 4AD and 5SI wormers are short acting as are 3ML products containing ivermectin or doramectin.

Combination Products

These are a mixture of a wormer plus a second chemical that will kill liver fluke.  These are only worthwhile in a limited number of circumstances.  In many cases, for different classes of stock, at different times of the year, simultaneous treatment for both worms and fluke is not required.  You should also check that the fluke treatment will target the correct age of liver fluke for the time of year.  Unnecessary use of combination products could allow worms and fluke to become resistant to the active ingredients at a faster rate.

Dual Active Products

A dual active product contains two wormers from different wormer groups.  The only dual active available in the UK is Startect which contains both a 3ML and a 5SI wormer.  The aim of this is to increase the length of time it takes for worms to become resistant to the product.  This product is ideal to use as part of quarantine treatment or as a mid/late season dose for lambs.  The group 4AD product (Zolvix) is also ideal to use at these times.

Others things to take into account when choosing a wormer include withdrawal period, whether you prefer a drench or an injection, the time of year and reason for treatment, cost and whether it is likely to work.  The most expensive product is one that isn’t effective.

Heather Stevenson,

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