Nematodirus (Nematodirosis) is a disease caused by the Nematodirus battus worm which affects young lambs and can result in a high number of mortalities.

The main difference in the lifecycle of Nematodirus battus compared with other parasitic worms is that development to infective larvae takes place within the eggs in the soil, the infection passes from one lamb crop to the next year’s crop. Cold weather delays hatching, this will occur once the temperatures reach 10 oC over a period of several days. If this temperature change occurs quickly over a short period of time, then a mass hatch may occur, typically occurring in late spring/early summer. When the mass hatching coincides with lambs increasing grazing activity this is when lambs will become infected. This can have a devastating impact.


Ewes do not show signs of the disease, only lambs are affected by Nematodirus. Sudden death and scouring in lambs aged 6 to 12 weeks may occur. Watery diarrhoea in young lambs will appear suddenly, with staining of the wool around the tail head. The lambs behaviour may also change, dull, depressed, reluctance to feed, loss of condition and a gaunt appearance caused by dehydration. The disease can result in death of the lambs, and if not treated soon enough there is considerable weight loss in the lambs.

Prevention and Treatment

  • ·        Avoid grazing pastures grazed by lambs during the previous grazing
  • ·        Remove sheep from infested pastures
  • ·        Treat with anthelmintic (consult with your vet)
  • ·        Use disease forecast


To assist farmers SCOPS (Sustainable Control of Parasites) produce a Nematodirus forecast. The forecast assesses the risk of Nematodirus infection to your lambs by combining grazing history alongside temperature data from 140 weather stations throughout the UK to predict the hatch date for Nematodirus. The timing of the risk to lambs will vary from region to region, the SCOP forecast is a useful tool to provide guidance to farmers.

The forecast can be found at: Nematodirus Forecast | SCOPS

Photo: Tom Costello