UNPREDICTABLE weather patterns could result in a high Nematodirosis risk in 2017. This is why it’s vital this year, more than ever, to keep checking the Nematodirus forecast, writes veterinary surgeon Rachel Mallet.

Nematodirosis is caused by the parasite Nematodirus battus and causes intestinal damage leading to profuse, watery diarrhoea. Nematodirus battus is a type of nematode (roundworm) and causes disease in young lambs which have never been exposed previously and so have no acquired immunity.

Life cycle: 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.

Following 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?

Frustratingly the highest risk period will vary slightly from year to year making it difficult to counteract. There are two significant factors to consider:

1) Environmental conditions. If the weather suddenly changes from cold frosty mornings to mild, warmer spring weather a mass hatching of parasites on the pasture occurs

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 very high

What other risks are there?

In addition to the two critical factors above there are other factors which will increase the challenge faced by lambs:

• Grazing lambs on the same pasture which they were grazed on last spring

• Presence of other parasites eg coccidiosis

• Other stress, triplets, fostered lambs, etc.

Clinical Signs

• Sudden onset profuse diarrhoea

• Faecal staining around the animals’ tail and perineum

• 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 five per cent 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.

Diagnosis

• Once worms are ingested they takes two to four 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

Treatment

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 seven to ten days after treatment are vital for determining efficacy of the treatment.

Prevention

Monitor the parasite forecast for your region daily so you are ready to act at the right time and prevent acute disease. Local knowledge on risk is invaluable so keep in contact with local vets and SQPs. Where possible, avoid grazing lambs on the same pasture on consecutive years.

• Visit the SCOPS or NADIS websites for the latest parasite forecasts.