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Another Challenge For This Year's Lambs - Nematodirus Warning As Spring Warms Up

SAC News Release Ref. No: 10N29
Published: 05 May 2010

Nematodirus battus threat (opens in new window)

As if things had not already been tough enough for this year’s lamb crop, SAC vets are warning they face a new threat as they switch from their mothers’ milk to eating grass.

After a cold spring, any warmth in early May will encourage a mass hatching of Nematodirus battus worms which can cause sudden death in lambs over six weeks old.  Early cases have already been reported in Inverness-shire during April.

The eggs of Nematodirus battus are very tough.  They are shed onto grass pasture by infected lambs and lie dormant until the following year, requiring a lengthy period of cold weather before the rise in spring temperatures causes larvae to hatch.  These are then swallowed by nibbling lambs and, in the gut, change into adult worms where the build-up can lead to sudden death.  Those lambs that do survive are often weak and sickly, having rapidly lost weight and appetite and with a watery diarrhoea.  A secondary infection with coccidiosis at this time can lead to kidney damage causing renal failure that increases losses.

Farmers should be aware the main risk factors include a late cold snap followed by warm weather (>10 C), pasture that carried lambs (or, occasionally, calves) the previous spring, lambs at 6 to 12 weeks old eating significant amounts of grass.  Permanent pastures and low ground grazing that is heavily stocked or has a history of the disease are also a risk.  If the Nematodirus hatch continues into June, hill lambs on improved pastures, which are relatively heavily stocked, may also be affected.

Lambs can be killed by the parasite before eggs appear in faeces so SAC vets advise that if unexplained deaths occur in lambs, freshly dead carcasses should be submitted to SAC Disease Surveillance Centres (DSCs) for post mortem examination. This will speed up diagnosis or rule out the condition.

If it is confirmed or where risk factors apply, then treatment should start once the lambs reach 6 weeks.  Don’t wait for signs of scouring, but treat with a wormer effective against Nematodirus – check the data sheet before purchase.  As the rise in worm numbers can be rapid, two doses, at 7-10 day intervals, are recommended. 

With severe problems the solution may be to move the ewes and lambs to low risk pasture (e.g. reseeded grass) if available.  Cattle don’t develop clinical disease due to Nematodirus but, if grazing with sheep, young calves can be infected, increasing the build-up of larvae in the field.  It is good practice to have faeces samples from all young stock checked regularly for evidence of worm eggs.  It is sound animal welfare and avoids needless dosing which can lead to the development of resistant worms.  SAC offers a Wormscan service on bulk faeces samples to reduce cost – further details are available from your local SAC Veterinary Centre.

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News Release Contacts

SAC Contact

Dr George Mitchell
Veterinary Investigation Officer
SAC (Scottish Agricultural College) Work Disease Surveillance Centre, Auchincruive,
Ayr
KA6 5AE
TelWork 01292 520318
Fax 01292 521069

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News Release Issued By

Mr Ken Rundle
Senior Communications Officer
SAC (Scottish Agricultural College) Work SAC, King's Buildings, West Mains Road,
Edinburgh
EH9 3JG
TelWork 0131 535 4196

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Notes for Editors

Group 1 (Benzimidazoles or BZs), group 2 (Levamisole) and group 3 (Avermectin) wormers are normally effective against N battus.

White drenches (BZs) should be effective against N battus even on farms where ineffective against other gut worms.