Please be aware that this website relies on the use of cookies to function correctly and involves some cookies being downloaded onto your device. This helps us to improve the content of the website so that it is more useful and relevant to you.
Allow cookiesPrivacy and Cookies Policy


Worms present a significant production threat to sheep with infection and financial implications for farmers so the aim of any worm control strategy is to balance the exposure of susceptible animals to high levels of infestation on pasture against the overuse of anthelmintics.

For more information visit SCOPS


Nematodirus is a key disease which can affect young lambs in spring and summer, with cases now also reported in Autumn. Signs include the rapid onset of profuse watery diarrhoea, and the lambs quickly lose condition. If left untreated, lambs can die due to dehydration, with 5% of lambs dying within a few days if there is severe larval challenge.7

In addition, changing climatic conditions have meant that disease caused by this parasite has been a real challenge for sheep over the last few years, so it’s essential to be aware of the threat and know how best to manage it.

What is resistance?

Resistance is the ability of worms to survive the normal dose of a wormer and pass that ability on to its offspring. Worms can be resistant to one or more class of wormer at the same time.

Resistance develops gradually over time. It can be slowed down significantly if SCOPS guidelines on anthelmintic use are incorporated on the farm. However, once you have solid resistance to an anthelmintic class (i.e. obvious treatment failures) it cannot be reversed.

Resistance to wormers often results in productivity losses due to a low to moderate worm burden left behind after treatment. The sooner you act to manage this, the better the results.