Worm treatment in sheep flocks at this time of the year can play a crucial role in farmers having a successful year. A worm burden in lambs can reduce growth rates by up to 50% with no clinical signs.

Pat McCambridge of College of Agriculture, Food and Rural Enterprise in its latest management notes asked are your lambs achieving an average weaning weight of 33kg at 16 weeks? (crossbred flocks).

This equates to an average growth rate of 250 g per day and means some of the best performing lambs should be finished at weaning.

He advised farmers to watch out for Nematodirus warnings during May and if seen use a recommended product. He said: “most farms will need to start the main worm dosing programme when lambs reach six weeks of age.It is generally a good policy to change or rotate dosing products used as this may help reduce the build up of wormer resistance on your farm. There are now five groups of products available to control worms in sheep.”

He added: “You can check the effectiveness of your wormer product by testing for worm eggs pre- and post-treatment of lambs. This can be arranged through your Vet where you can sample the faeces from a particular batch of lambs pre- and post-treatment.”

Farmers need to anticipate the risk of infection as the parasite acts quickly and mortality is high.

The following factors need to be considered
• Sudden cold weather followed by a period of warm weather
• Lambs old enough to be eating significant amounts of grass normally six weeks and older
• Lambs grazing pasture that was grazed by lambs last spring
• Heavy stocking density
• Lambs under stress such as twins or triplets who may be consuming more grass, or suckling ewes with less milk, these lambs may be at risk from a younger age