SCOPS Nematodirus Warning for Sheep Farmers

Sheep farmers must be on their guard against Nematodirus now that the weather has warmed up, warns SCOPS.

Such a sudden change from cold days and frosty nights is when Nematodirus is at its most dangerous with a mass hatch of over-wintered parasites forecast. Farmers are urged to consider the risk factors (see pdf below) and consult their vet or adviser with regard to local risks and treat lambs that are at risk.

Nematodirosis 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 worm, Nematodirus battus, which has a different life-cycle to other sheep worms. Under certain climatic conditions it can strike very quickly, with little or no warning.

The main difference in the life-cycle 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, as we have this year, 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 6 weeks old), the result can be devastating.

‘Because this disease strikes so quickly, we can’t afford to have a ‘wait and see’ policy with Nematodirus. The damage is done by large numbers of immature larvae that are not producing eggs so Faecal Egg Counts (FECs) are also not reliable’ says Lesley Stubbings, of SCOPS. ‘Farmers must act quickly, on the basis of risk assessment and advice on the level of challenge in their area.

The main risk factors to consider are:

·         A sudden, late cold snap followed by a period of warm weather

·         Lambs grazing pasture that carried lambs last spring

·         Lambs that are old enough to be eating significant amounts of grass (generally 6–12 weeks old but this year may be younger with ewes struggling to milk)

·         Groups where there is also likely to be a challenge from coccidiosis

·         Lambs that are under other stresses e.g. triplets, fostered, on young or older ewes.


If farmers feel their lambs are at risk and they need to treat for Nematodirus, then SCOPS advises farmers to use a white (1-BZ) drench. These are highly effective against this parasite and suitable for young lambs. It may be necessary to treat lambs more than once depending on the spread of ages in a group and subsequent weather conditions.

Watch out for Warnings for your region on

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 later in May or early June. SCOPS will be giving a guide as to the risk in various regions on a week by week basis.

For more information visit





19th April 2013

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