Nematodirus in Lambs: Prevention is Better Than Cure

Nematodirus in Lambs: Prevention is Better Than Cure Nematodirus in Lambs: Prevention is Better Than Cure

The annual menace of Nematodirus battus, causing acute, severe diarrhoea still leads to sudden dehydration and lamb deaths on many farms. As the onset of disease can be very sudden, farmers have to be vigilant and respond rapidly with appropriate anthelmintics. In this article, we look at why it is essential for farmers to be prepared for the threat of nematodirus this year, and how they can do so. 

The need for vigilance is particularly true for 2020, as unusual and unpredictable weather patterns mean farmers will find it more difficult to predict when this parasite may strike. Vigilance and preparedness must therefore be a key priority for farmers. SCOPS tell us, 'we can't afford to have a 'wait and see' approach with nematodirus', and this is advice that should be born in mind by all sheep farmers this season.

Nematodirus is a serious and nasty parasite in lambs. In the worst case scenario it will kill up to 5% of the lamb crop, and at best it will have a significant impact on growth rate and live weight gain. The extra time to finish will increase your costs and erode your margins.

Thankfully, adult sheep acquire natural resistance following exposure therefore we do not have to worry about the impact on them. As the lambs have never encountered Nematodirus battus previously, they have absolutely no protection from it and it can quickly overwhelm them.

The risk period begins when the weather suddenly changes from cold winter frost to warmer spring weather. This is due to a mass hatching of parasites which survive the winter on the pasture. If this coincides with lambs beginning to eat significant amounts of grass (6 - 12 weeks old) it can have devastating effects. The impact varies depending on factors such as the weather and region, with problems becoming apparent earliest in the milder, southeast of the UK, and later in Northern England and Scotland. The risk is possibly greater this year, due to the unpredictable weather patterns we have been experiencing. An initially mild January, was followed by sudden arctic blasts, with a return to double digit figures only days later, and if these sudden and unpredictable temperature fluctuations continue the appearance of Nematodirus may surprise farmers and leave their lambs vulnerable.
The best way to stay informed is to monitor the parasite forecast for your region and keep in contact with your vet and SQP who will also be monitoring this. It can be easily accessed online at or Due to the quick-striking nature of Nematodirus, it is vital that farmers have this issue at the front of their minds and are ready to take action.

Nematodirus is unusual because the larvae develop inside the egg on the pasture. As soon as the mass hatching is triggered by the weather change they are active and ready to infect lambs. Rather than being passed from adult sheep to lambs like many other parasites, they are passed from the previous year's lamb crop to this year's via the pasture, making it particularly difficult to control.

Nematodirus Strikes Fast – Be Ready 

Nematodirus is a very difficult disease to counteract as it strikes very suddenly so it is important to prevent it and pre-empt when it is likely to be an issue.

Disease is caused by the large number of infective larvae ingested so unfortunately we cannot wait for symptoms to appear as severe damage will already be inflicted; resulting in massive losses in terms of mortality and production. Lambs which do survive can take an extra 2-3 months to reach market condition.

Signs of Nematodirus infection: 

  • Sudden onset profuse diarrhoea
  • Faecal staining of tail and perineum
  • Dull/depressed lambs
  • Lambs which stop sucking
  • Gaunt condition
  • Dehydration
  • Rapid loss of body condition
  • Lambs congregating around water to rehydrate


Sadly faecal worm egg counts (FWEC) are not useful for acute Nematodirus infection as it takes 2-4 weeks for the larvae to begin to produce eggs. Waiting this long to take action would be catastrophic. Nematodirus infection is based on clinical signs and post mortem. FWEC are absolutely vital for monitoring response to treatment following infection.

High Risk Factors for Nematodirus Battus: 

If any of the following apply your lambs will be at greater risk of nematodirus and you must be more vigilant:

  • Lambs grazing pasture that carried lambs the previous spring
  • A sudden, late cold snap which is followed by a period of warm weather
  • Lambs that are old enough to be eating significant amounts of grass (6–12 weeks old)
  • 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


Thankfully treatment with an appropriate white drench, is highly effective and is endorsed by SCOPS, who comment in their 'Nematodirus in Lambs' literature, '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 normally highly effective against this parasite and suitable for young lambs. This includes 2.5% albendazole, which is highly effective, relatively inexpensive and appropriate for lambs.

It is extremely important to dose for the correct weight of lamb to ensure we do not select for resistance. A FWEC is recommended 7-10 days after anthelmintic drenching to ensure that the treatment has been effective. It must be noted that severely affected lambs may require multiple treatments which you vet will be able to advise you on. Usually, for lambs born from the second week of March onwards, treatments are given 3 weeks apart in May. In greater risk years, three anthelmintic treatments are given extending the drenching period into June. Remember this can vary from year to year depending on the weather so follow your vet's advice.


Where possible avoid grazing lambs on the same pasture on consecutive years.

Look at or for the Parasite Forecast, advising when the risk period is coming and pay attention to the weather patterns in the spring period.

Finally many vets are issuing warnings to their clients when the risk period is predicted so keep in contact with your local practice.

To avoid a Nematodirus outbreak, and the associated costs and stress, make sure you are ready to strike back.

For more advice, speak to your local animal health advisor or vet.

This information was provided by Bimeda the makers of Endospec 2.5% (2.5% albendazole oral drench*)

Use Medicines Responsibly.

Table 1: Anthelmintics effective against nematodirus*

Group Active Ingredient Product Examples Can be used in sheep? Effective Against Nematodirus Battus?
Benzimidazoles Albendazole Endospec 2.5% oral suspension, Rycoben 2.5% oral suspension. x x
Oxfendazole Parafend 2.265% oral suspension, Bovex 2.265% oral suspension. x x
Fenbendazole Panacur 10% x x
Levamisoles Levamisole Levacur SC 3%, Levasure 7.5% x x
Macrocyclic Lactones Moxidectin Cydectin 0.1% oral solution x x
Doramectin Dectomax 10mg/ml injection x x (L4 only at standard dose)
Amino-Acitonitrile Derivative (AAD) Monepantel Zolvix 25mg/ml oral solution x x
Spiroindoles Derquantel Startect Dual Active Oral Solution for Sheep (Derquantel 10mg/ml & Abamectin 1mg/ml x x

*Speak to your local vet or SQP to determine which active ingredient is most appropriate for your circumstances

*Endospec 2.5% is a POM-VPS Medicine.

Bimeda supports the responsible use of anthelmintics.

Care should be taken to avoid the following practices because they increase the risk of development of resistance and could ultimately result in ineffective therapy:

  • Too frequent and repeated use of anthelmintics from the same class, over an extended period of time.
  • Under dosing; this may be due to underestimation of body weight, mis-administration of the product, or lack of calibration of the dosing device (if any)


Tel: 01248 725 400
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Address: Bimeda, 2 Bryn Cefni Industrial Park, Llangefni, Anglesey, Wales, LL777XA

Mary Murphy, Marketing Manager
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