Nematodirosis is a severe parasitic disease of lambs six to twelve weeks of age which become infected through ingesting large numbers of infective larvae from grazing on contaminated pasture.
The life cycle of the causative worm, Nematodirus battus, is unlike that of other roundworms in that typically it takes almost a year on pasture before the egg hatches releasing the infective larva. There is a mass hatching of eggs in spring when the soil temperature increases after a period of cold weather and disease typically occurs in April, May and June.
After ingestion by lambs, Nematodirus larvae invade the wall of the intestine. Infection is characterised by profuse diarrhoea, dehydration and weight loss. In outbreak scenarios, lambs can be seen congregating around water troughs due to the severe thirst that develops, while the ewes which are unaffected continue to graze.
This disease is best prevented by keeping the current year’s lambs off pasture that was grazed by lambs or young calves (which can be carriers of infection) in the previous year. Enterprises with high stocking rates are particularly vulnerable. Please note that twin lambs, or single lambs born to ewes of poor milking ability may be at a greater risk of developing disease as they begin consuming greater amounts of grass earlier in life. If ‘clean’ pasture is available, preference should be given to moving these lambs first.