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Unpredictable weather patterns could result in a high Nematodirosis risk in Spring 2018. This is why it’s vital to keep checking the Nematodirus forecast to determine if and when your lambs are at risk.

Nematodirosis is a deadly disease which can strike in young lambs. The parasite Nematodirus battus is ingested from pasture and where high burdens are present can cause severe intestinal damage resulting in profuse, watery diarrhoea and even death.

Sheep often become infected by roundworms passed from animal to animal, via the pasture, in the same grazing season. Nematodirus battus is different because it is transmitted from the lambs grazing the pasture in the previous season to those grazing in the current season. This makes it particularly difficult to control.

Nematodirus Life CycleFollowing ingestion of infective larvae on the pasture they go on to develop into adult worms which can produce eggs. This takes as little as 14-21 days. These eggs then pass out in the faeces resulting in greater pasture contamination.

Depending on the weather conditions these eggs will either go on to develop into infective larvae which can infect lambs immediately or they will lie dormant until the following Spring when they can infect the new crop of lambs which have never been exposed to them and so have no natural immunity.

Thankfully once lambs have been exposed they begin to develop natural immunity however nematodirus is capable of causing a great deal of damage, and even death, before this immunity develops.

When Is The Risk?

This is a disease which can be unpredictable and the high risk period does not occur at the same time every year. There are two significant factors to consider:

  1. Environmental conditions. If the weather suddenly changes from cold frosty mornings to mild, warmer spring weather this is the perfect trigger for a mass hatching of parasites on the pasture.'
  2. Lamb age/weaning. If this mass hatching occurs around the same time that lambs are beginning to consume significant amounts of grass (6-12 weeks) then the risk will be high.

What Other Risks Are There?

In addition to the two critical factors above there are others which will increase the challenge:

  • Grazing lambs on the same pasture which lambs were grazed on last Spring
  • Presence of other parasites e.g. coccidiosis
  • Other stress, triplets, fostered lambs etc.

Clinical Signs

If you observe any of the following clinical signs in lambs in Spring then contact your vet/SQP for advice:

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

Why Should I Be Worried?

First and foremost nematodirus will impact on the welfare of the lambs. Nematodirosis also comes with a significant cost. If all of the risk factors come together and present a high challenge then up to 5% of the lamb crop may die. Even if you are able to avoid deaths in a nematodirus outbreak the lambs will lose condition and will take longer and cost more to finish.


  • Once worms are ingested they take 2-4 weeks to begin producing eggs so faecal egg counts are not helpful for acute disease however they should be used to monitor response to treatment.
  • Presentation/clinical signs
  • Post Mortem


SCOPS recommend that, if treatment is required, a group 1 (white/1-BZ) wormer should be used. When treating lambs weigh them and dose accurately to ensure that treatment is effective and to help protect anthelmintics from resistance. Faecal worm egg counts 7-10 days after treatment are vital for determining efficacy of the treatment.


Monitor the parasite forecast for your region so you are ready to act at the right time and prevent acute disease. This can be accessed on the SCOPS and NADIS websites and should be checked daily during periods of high risk. Local knowledge on risk is invaluable and so you should keep in contact with your local vets and SQPs. Where possible avoid grazing lambs on the same pasture on consecutive years.

About the Author

Rachel Mallet is a Veterinary Surgeon, who now works as a Professional Services Vet providing technical support to vets, SQPs and farmers in the UK. Rachel is passionate about animal health and about promoting best practice and preventative medicine amongst farmers.

Date editorial prepared: January 2017
Use medicines responsibly. Noah.co.uk/responsible.
*Endospec 2.5% contains albendazole 25 mg, selenium (as sodium selenite) 0.27mg, cobalt (as cobalt sulphate) 0.624mg per ml.

The following active ingredients have indications for nematodirus in sheep. Please consult your SQP or vet to determine which is most appropriate and consult the SPC data sheet for further information: Albendazole, ricobendazole, oxfendazole, Fenbendazole, levamisole, moxidectin, doramectin, monepantel, derquantel/abamectin.

SCOPS. Nematodirus in Lambs Alert

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