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Protect your flock with an effective worming strategy.


NEMATODIROSIS is a severe parasitic disease generally seen in lambs between six and 12 weeks old.

The disease is caused by the nematode worm nematodirus battus. Lambs become affected when they ingest large numbers of the infective larvae from pasture contaminated by young lambs the previous year.

The larvae develop slowly inside the egg, which protects them from the environment. Hatching normally occurs between March and May, after the egg has undergone a period of cold weather and the environmental temperature has risen above 10C stimulating development.

A mass hatch of the eggs can occur leading to large numbers of infective larvae being present on the pasture and giving rise to explosive disease. Winter and spring weather conditions have a large effect on the likely prevalence of disease with cold winters leading to a late hatch with more problems.

The mild winter and warm weather we had in March is likely to have led to an early hatch, before the main lambing got underway in our area. This should hopefully lead to reduced pasture infestation and low levels of disease. The current prediction for disease in the North of England this year is low, but another projection will be produced this month which may alter this outlook.

Clinical signs are usually seen about two weeks after initial infection when the lambs show profuse watery diarrhoea with staining of the wool around the back end. It is not unusual for 5% of lambs to die if the condition is severe, recovered animals suffer a severe growth check and may be stunted. Acute disease is caused by the developing larvae and adults in the guts, so faecal worm egg counts are not useful, but post mortem examinations may demonstrate large numbers of developing worms in the small intestine.

Control is by clean grazing and/or strategic dosing with anthelmintics. The difficulties associated with clean grazing are that pastures used to graze lambs one year should not be used the next, this can be problematic as grazing is often at a premium as lambing progresses.

Anthelmintic treatments for nematodirosis should be carried out based on the parasite forecast and perceived risk.

They can be given at three weekly intervals over the predicted period of risk. Benzimidazole wormers (white drench) are cheap and generally effective; resistance to these drugs has been identified in the UK but it is very uncommon. Ensure the correct volume of drench is given as under dosing will make the treatment ineffective and lead to resistance.

Avermectins do not appear to have a persistent activity against nematodirus battus, which they do against some other worms. Take this into account when planning your worming programme, both from a cost and resistance point of view.

Flock health planning with your vet will make your worming strategy more effective, slow resistance and probably increase production.

By Iain Carrington of Intake Vets
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Copyright 2012 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Features
Publication:The Journal (Newcastle, England)
Date:May 12, 2012
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