19th May 2019

Nematodirus – a Refresher.

As we move into spring, we thought it timely to write a quick refresher about diarrhoea in young lambs, particularly that caused by Nematodirus. These roundworms are an important cause of disease in lambs. The eggs of the worm are extremely hardy, surviving the freezing winter temperatures to cause disease the following year. For this reason, Nematodirosis is mostly seen in young lambs grazing pastures that lambs grazed the previous year.

The disease is only seen in lambs, ewes do not show signs. Usually, lambs are seen to suddenly develop profuse diarrhoea. They are often stained at their back ends and become dull and depressed in themselves. They tend to stop sucking and become dehydrated and rapidly lose condition, which eventually causes death if left untreated. Deaths usually extend to up to 5% of the lambs and those remaining are often poorer, requiring up to three months longer to reach target weight. This obviously makes for quite a financial loss.

It is often difficult to accurately diagnose nematodirosis as disease often occurs before eggs can be found in faecal samples. However, post mortem of lambs that have died can be very helpful in detecting the larval stages and adult worms in the gut. Often, treatment will be recommended based on suspicion of nematodirosis or absence of other parasites on faecal tests. It can be easy to confuse nematodirosis with coccidiosis as both cause diarrhoea in large numbers of lambs.

NADIS produce disease outlooks frequently and these can be useful in planning for Nematodirus treatment. Overuse of parasiticides has led to resistance but currently, group 1 anthelmintics can be used if treatment is needed. As always, prevention is better than cure so we suggest you consider the following steps:

  • Avoid grazing lambs on the same pasture that was used the previous year. Adult sheep are highly resistant so they can be grazed on this pasture instead.
  • Speak to your vet to decide on the best plan of action based on your management system and risk level.
  • Take note of the Nadis parasite forecast and act accordingly.
  • Currently, the risk period is as the temperature rises so anthelmintic treatment against nematodirus is likely needed for lambs born from mid-March onwards. In years with a normal forecast, this can mean two treatments three weeks apart. In heavier burden years, this may mean a third treatment going on into June. Again, discuss
  • your current regime with your vet.

If you have any questions about Nematodirosis or diarrhoea in lambs, please don’t hesitate to call us.