Nematodirus Alert

The SCOPS forecast is currently showing large areas of the UK as having a high or very high risk for Nematodirus in young lambs. Is your flock at risk of infection and what can you do to prevent adverse effects in your lambs?

What is Nematodirus?

  • Nematodirus battus is a roundworm that causes death and scour outbreaks in young lambs. The worm over winters on the pasture which allows it to pass from one year’s lamb crop to the next.
  • It mainly occurs in late spring /early summer months and lamb’s deaths can reach 5%. Lambs that survive suffer a marked check in growth rates (2-3 months longer to reach market weight).
  • It is a seasonal disease requiring specific weather conditions to become active. Before they can hatch, the eggs must undergo a period of cold weather followed by warmer temperatures of 10°C or more. If this happens over a short time frame, there will be a mass hatch of infective larvae which will infect your grazing lambs. The hatch can occur very quickly and so vigilance is very important.
  • Timing will vary from region to region. In the south of England for example, it is likely to occur earlier in April/May; in northern England and Scotland it may be early June. In 2019, with the weather being so unseasonably warm in February, it is likely to be earlier across the board. The SCOPS forecast was set up to predict hatching so that farmers are aware of the risks before they occur.



Are your lambs at risk?

  • Do you have this year’s lambs on a pasture that carried lambs at the same time of year, last year?
  • Are the lambs old enough to be eating significant amounts of grass? (generally, 6-12 weeks of age but may be younger if ewes are not milking well)
  • Has there been a sudden, cold snap recently followed by a period of warm weather?
  • Do the SCOPS forecast map show moderate/high or very high risk in your area?
  • Are your lambs under other stresses e.g. triplets, fostered, on young or older ewes?

What to do if you are at risk?

  • Avoid infection by moving your at-risk lambs onto pasture that was not grazed by lambs last year.
  • If this is not possible – TREAT


  • Speak to your vet for advice on treatment
  • White is Right!
  • Use a white (1-BZ) drench for your lambs.
  • This is effective against Nematodirus as resistance levels are low compared to other worms affecting young lambs and it relatively cheap to buy.
  • Make sure you dose the lambs correctly –
    • Ensure the lambs are weighed and are dosed for the heaviest animal in the group
    • Check the calibration of your dosing gun.

Are your animals already affected?

  • Lambs will:
    • Have sudden onset of profuse watery faecal staining of the wool of the tail and perineum.
    • Be dull, depressed and stop feeding from the ewe
    • Have a gaunt, dehydrated appearance and loose condition
  • Ewes do not show disease.


  • It is important to remember that this parasite causes damage with the large number of immature larvae that your lambs will ingest from the pasture and at this stage, there is no egg production by the parasite.
  • Faecal egg counts (FEC) are NOT a reliable assessment of the risk to your farm.
  • Coccidiosis is also an important parasite at this time of year and so if animals are showing clinical signs or not responding to the wormer it is worth contacting your vet for further information.
  • Monitor clinical signs and the SCOPS parasites forecast. Post mortem can help diagnose Nematodirus (and rule out any other causes).

If you are worried about Nematodirus affecting your flock or would like to discuss any areas of parasite control please contact your local Westpoint practice.

Written by Sarah O’Reilly DVM, MRCVS

Sarah graduated firstly with a degree in Agricultural Science from UCD Ireland. She then moved to Slovakia to study, graduating as a vet in June 2016 and joined Westpoint as an intern. Having grown up with animals all her life, she has a strong interest in cattle having a purebred Shorthorn herd at home in Dublin. She has a particular interest in reproduction and fertility.