SCOPS Nematodirus Forecast, Risk factors, Action & Treatment

March 22, 2022

The SCOPS Nematodirus forecast predicts the hatch date for Nematodirus based on temperature data from 140 weather stations throughout the UK.

At Towcester Farm Vets we monitor the three weather stations in our area and put a notification on our Facebook Page if the forecast status in our area changes.  The stations we monitor are Church Lawford, Bedford & Woburn.  If you follow us on Facebook we’ll let you know as soon as one of those stations indicates a change in its status.

The information below is based on the material on the SCOPS website and is designed to be used in combination with your grazing history (more below) to assess the risk of your lambs becoming infected.

Using the SCOPS forecast

  1. Use the SCOPS map to locate the station(s) closest to your holding.Use knowledge of your farm and the surrounding area to choose a weather station that is most relevant to you. In most cases this will be the nearest station but if, for example, there is a large difference in the height above sea level between your holding and the nearest weather station, then look to see if another station further away may be more representative. If you click on a station on the SCOPS map, it will give the height above sea level. Alternatively take a view across a combination of stations in your area.
  2. Click on the station(s). Each station has more detailed information on the current risk level, guidance on what to do next, and information on when the forecast was last updated.
  3. Carry out a risk assessment and take action if needed.  See below for more information on how to assess risk and what action to take.
  4. Consider additional information to the forecast map. 
    • The map predicts hatch date on temperature data, but the risk will vary from farm-to-farm and from field-to-field. When deciding whether or not to act, it is important to assess the risk to each group of lambs based on the history of the field, its aspect and altitude.
    • South-facing fields tend to have an earlier hatch and, as a guide, every 100m increase in altitude will delay hatching by about seven days. So, for example, if your nearest weather station on the map is at 200m above sea level and your farm is 100m above sea level, hatching could be around seven days earlier than the forecast.
    • You can also click here to see a table capturing data from the map over the previous weeks, so you can see when the dot indicating your nearest weather station changed colour. You will need to know the name of your nearest station to find it in the table, so click on that station on the map above to check the name.

Understanding Nematodirus  

Nematodirus is a particularly nasty disease in lambs, causing a high number of mortalities and stunting the growth of many others. It is caused by the Nematodirus battus worm, which has a different lifecycle to other sheep worms. Under certain climatic conditions it can strike very quickly, with little or no warning. The main difference in the lifecycle of Nematodirus battus compared with other parasitic worms is that development to infective larvae takes place within the egg and infection passes from one lamb crop to the next year’s crop. Cold weather delays hatching so when we get a sudden change in temperature it can trigger a mass hatch. If this coincides with the time when lambs are starting to take in significant amounts of grass (over about six weeks old), the result can be devastating.

Nematodirus can strike very quickly so you can’t afford to have a ‘wait and see’ policy. And because the damage is done by large numbers of immature larvae that are not producing eggs, faecal egg counts (FECs) are not a reliable indicator of risk. Rapid action is often required and this has to be based on a risk assessment and the forecast for your area.

Main risk factors

If your lambs are grazing pasture that carried lambs last spring and you answer yes to one or more of the four questions below, then your lambs are at risk.

  1. Are your 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)
  2. Do you have groups where there is also likely to be a challenge from coccidiosis? For example, mixed aged lambs are a higher risk
  3. Has there been a sudden, cold snap recently followed by a period of warm weather?
  4. Have you got lambs that are under other stresses e.g. triplets, fostered, on young or older ewes

Recommended actions

  • If possible, avoid infection. Move at-risk lambs (as determined by the risk assessment) to low risk pastures (i.e. pasture that was notgrazed by lambs the previous spring).
  • If you cannot avoid high risk pasture grazed by lambs the previous spring and decide you need to treat for Nematodirus, SCOPS advises farmers to use a white (1-BZ) drench. Check that treatment is effective by taking a FEC 7 to 10 days after treatment. Remember, it may be necessary to treat lambs more than once depending on the spread of ages in a group and subsequent weather conditions.

The timing of a potential problem 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.


As explained above, SCOPS advises farmers to use a white (1-BZ) drench when treating. These are normally highly effective against this parasite and suitable for young lambs. However, the first confirmed case of Nematodirus resistant to the 1-BZ group was reported in 2011 and so farmers are advised to follow the SCOPS guidelines on correct drenching technique and dose carefully to the correct weight of the lambs and to check afterward if the treatment has been fully effective. If in doubt speak to one of our vets by calling us on 01327 350239.


Strictly Necessary

These cookies are required for our website to operate and include items such as whether or not to display this pop-up box or your session when logging in to the website. These cookies cannot be disabled.


We use 3rd party services such as Google Analytics to measure the performance of our website. This helps us tailor the site content to our visitors needs.


From time to time, we may use cookies to store key pieces of information to make our site easier for you to use. Examples of this are remembering selected form options to speed up future uses of them. These cookies are not necessary for the site to work, but may enhance the browsing experience.


We may use advertising services that include tracking beacons to allow us to target our visitors with specific adverts on other platforms such as search or social media. These cookies are not required but may improve the services we offer and promote.

Change Settings

Welcome. You can control how we use cookies and 3rd party services below

Change Settings Accept
Learn how we use cookies