Farm Ireland

Friday 15 December 2017

Declaring war on worm nightmare

Wormers, used correctly, can boost lamb growth and profits

Charles Chavasse

Lambing is now over and ewes and lambs are happily outside grazing grass. The warm, damp weather we experienced this spring gave a great boost to grass growth.

However, it should be remembered that these conditions are also ideal for the development and transmission of the worm parasites that affect sheep and cattle.

Some of these worms will have survived the winter on the pasture; others will have survived in the ewes to be shed around lambing time when the ewe's immune system is compromised.

Lamb growth rates can be affected by heavy worm burdens even before they show signs of scouring, so treat ewes with a persistent wormer to reduce the threat.

Once lambs are 6-8 weeks old they should be dosed or dung samples should be examined for the presence of worm eggs. Traditional white, yellow and clear drenches need to be used every 3-4 weeks as they have no persistent activity in sheep.


Moxidectin drenches offer five-week activity and during this time all susceptible worms that are consumed are killed. Effectively, the lambs work as 'hoovers', cleaning the pasture of infective larvae. This allows the dosing interval to be extended to at least eight weeks. The other advantage of using a moxidectin is that lambs can be sent for slaughter 14 days after treatment, so it offers great flexibility when marketing lambs.

On many farms, the first worm to cause problems in the spring is nematodirus battus. This infection passes from one year's lamb crop to the next on the pasture.

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None of the wormers have a persistent action against nematodirus, so the first dose for the lambs has to be timed using past knowledge of the farm and keeping a close eye on the lambs. If a dark-to-black scour is seen in the spring then action is required, but it must be remembered that coccidiosis can also cause lambs to pass very dark scour.

There is concern that resistance to some wormers may be developing in our sheep populations. In Ireland, there have not been any reported cases of resistance to moxidectin yet. However, it is important that sheep farmers develop worming programmes with their vets and advisers to avoid selecting for resistance.

Wormers should only be used when required and farmers are encouraged to use the diagnostic tool where faecal samples are examined for worm egg content. This information is helpful to identify when lambs need to be dosed.

The service is available from the Regional Veterinary Laboratories or through your local vet. It is vital that the correct volume is used and that the dose rate is calculated for the heaviest lamb in the group.

Equipment must be correctly calibrated and the animals adequately restrained so that the dose is easily and effectively delivered.

In the past, it was recommended that lambs should be dosed and moved onto clean pasture, but now it is recognised that this might select for resistance. As a result, it is now advised that animals should either be moved and dosed a week later or dosed and moved at a later date depending on the wormer being used. Alternatively, leave 10pc of the lambs untreated.

Farmers should talk to their vets or advisers and get a plan in place now. Using a wormer with persistent activity will reduce the number of doses that lambs will require, improving growth rates, reducing labour and stress on lambs from repeated handling.

Charles Chavasse is a vet with Pfizer

Indo Farming