Nematodirus: a Perennial (but changing?) Problem in Lambs

Moredun-logoSummary written by Dave Bartley BSC Phd, Fiona Kenyon BSc, PhD and Frank Jackson BSc PhD

Taken from Moredun Foundation Newsheet Volume 5 No. 9 (2011)




  • The principle effect of infection with Nematodirus is scouring, although this can also be associated with other bacterial/viral/protozoal (coccidian) infections.
  • Signs of heavy infection are profuse, watery yellowy-green diarrhoea which leads to severe dehydration, and mortality in some cases. The fleeces of infected animals can become dull and rough and the animals may show a “tucked up” appearance. Onset of disease can be extremely rapid and mortalities can occur before eggs appear in faeces.
  • Less heavy infections reduce appetite and productivity resulting in classical ‘ill thrift’.
  • The unique epidemiology of Nematodirus battus leads to synchronised hatching behaviour and consequently the highest risk of disease occurs in the spring in young lambs (4-8 weeks old).
  • Although thought of as a spring disease in very young lambs, in recent years, outbreaks of the disease have been seen in older lambs later during the grazing season.
  • Risk of disease forecasts can be found at
  • Speak to your veterinary surgeon or advisor to ensure that you use a suitable anthelmintic to control nematodirosis on your farm.



sheep cover2 smMore information on disease prevention can be found on the DVD 'Managing Your Flock for Peak Health' - programme 2 in the series 'Sheep on Your Smallholding'.







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