Vets from Scotland’s Rural College fear young lambs are at risk from a mass hatch of Nematodirus battus worms they expect in the next few weeks.
The worms, which climb onto blades of grass which are then eaten by lambs as young as six weeks old, can cause sudden deaths, while those that survive are left sick and weakly with a watery diarrhoea. It is yet another challenge to stock suffering the after effects of two difficult years.
According to Dr George Mitchell of SAC Consulting, Veterinary Services in Ayr (part of SRUC, Scotland’s Rural College):
“The risk of an outbreak increases when a cold period in the spring is followed by a warm spell leading to a mass hatch of eggs on pasture. So far this year spring temperatures have been exceptionally low, so it is likely that a mass hatch of dangerous larvae will occur from mid May onwards, posing a threat to the lamb population from six weeks of age throughout Scotland”.
This news comes at a time when the recent autumn and winter means many famers have faced severe problems. Ewes are in poorer condition than they would like, late snow has killed sheep and lambs in some areas, while across Scotland other diseases like liver fluke are creating additional worries.
Nematodirus battus worms are a particular problem in the spring when young lambs start to eat more grass. In addition to the initial effects of Nematodirus disease there is a risk of associated coccidiosis and kidney damage which increases losses.
The worm eggs are particularly resistant to the elements, therefore the number of larvae hatching on a pasture tends to increase year on year, rising to a level where serious disease occurs. Permanent pastures and heavily stocked low ground grazing are particularly at risk, as are pastures with a history of the disease.
“The Nematodirus hatch may well continue into June”, warns George Mitchell. “This will affect hill lambs on improved pastures which are relatively heavily stocked. The parasite can kill lambs before eggs appear in sheep dung so for a proper diagnosis it is important that freshly dead lamb carcasses should be submitted to SAC Consulting, Disease Surveillance Centres for post mortem examination”.
The advice from the SRUC experts is that when the risks are high lambs should be treated with a wormer effective against Nematodirus from six weeks of age. Because of the extremely rapid rise in worm numbers on pasture, two anthelmintic doses at 7-10 day intervals are normally recommended for most situations. Where there is a particularly severe problem the best solution may be to move the ewes and lambs to low risk pasture (eg reseeded pasture) if available.
Cattle do not develop clinical disease due to Nematodirus. However young calves grazed on pasture which carried lambs in the previous year can become infected. This allows infection to be carried forward to the following year’s lamb crop where rotational grazing is carried out.
Finally Dr Mitchell reminds farmers that a second hatch of Nematodirus eggs has been recorded in the autumn in some areas. It is associated with wet weather, potentially threatening hoggs or store lambs. Casualty animals and/or faecal samples should be submitted to check for this possibility.
To see the most current risk information for their area farmers should visit the SCOPS webpage where a regularly updated risk map is available.
For further information contact Dr George Mitchell on 01292 520318 or e mail George.Mitchell@sac.co.uk.
SAC Consulting, Veterinary Services offer a Wormscan service on pooled faeces samples to reduce cost – further details are available from any local SAC Consulting Veterinary Surveillance Centre.