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Nematodirus Hatching…….

5 May 2022

The warm weather has been a welcome return for grass growth and conditions for outdoor lambing.  However, this warmer weather has made ideal conditions for Nematodirus battus hatching.  They favour a period of cold weather followed by a cumulative period of 7-10 days of temperatures over 11ºC.  Nematodirus eggs on the pasture shed by lambs last year will have survived through winter and will hatch in the right conditions now.

A fantastic resource is available at the SCOPS online Nematodirus forecast ( which is currently (29/04/22) indicating a wide range of risk levels across south-west Scotland and the north England.

  • Ayr and Carlisle are flagged as very high risk (black),
  • Eskdalemuir and West Freugh as moderate (orange)
  • Dundrennan as low (yellow) and this may change quickly in the coming days.


This forecast predicts when they hatch they will occur in different parts of the country, although the altitude and aspect of your fields may alter the precise timing of hatch on your farm, with higher altitudes and north facing pastures delaying the hatch.


In Scotland, nematodirus cases are often found in May, with a peak of diagnosed cases in June.  This follows the weather, as well an increased intake of grass by lambs (often 6-8 weeks of age).  The first sign of nematodirus in lambs is often sudden death.


To minimise the risk, look at the risk of your grazing fields.  Fields grazed by 6-12 week old lambs in previous years will be high risk, especially if there was an outbreak in that field last year.  Treatment of affected animals with white drench (1-BZ) is recommended in periods of high risk. To date, Nematodirus resistance to white drench has only been identified in a small percentage of flocks.  The SCOPS Nematodirus forecast alongside knowledge of your own farm and annual grazing patterns should help with deciding on the timing of treatment.


Kirsten Williams, SAC Senior sheep and beef consultant


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