The Department of Agriculture is advising farmers about the predicted risk of infection of Nematodirosis in livestock after it received advice from the Nematodirus Advisory Group.

The Department says the severe disease affects six to 12 week old lambs, which become infected through ingesting large numbers of infective larvae present on contaminated pasture.

The life cycle of the parasitic disease is unusual in that, typically, there is a mass hatching of larvae in spring when the soil temperature increases after a period of cold weather, it says.

Infection in lambs is in the form of dehydration, profuse diarrhoea and weight loss and mortality can be high in untreated lambs, the Department says.

The larvae of the disease invade the intestinal mucosa of the lamb after ingestion and in some cases death may occur before signs of diarrhoea are observed, it says. Ewes will appear clinically normal.

The Department says the disease is best prevented by keeping the current year’s lambs off pasture that was grazed by lambs last year.

Mean soil temperatures for March this year were slightly colder almost everywhere than their long-term average. The maximum Nematodirus larval count is expected by the start of April in the south-west and spreading to the rest of the country by the middle of the month, it says.

The Department says that nationally the weather conditions leading to maximum larval occurrence were similar to last year and in line with normal conditions (normal conditions are defined as the average of weather conditions between the years 1981 and 2010).


Lambs may show clinical signs of infection two to three weeks from these dates of peak hatching and in the south and west, lambs should be dosed with a suitable anthelmintic from mid to late April, it advises.

Lambs in the rest of the country should be dosed from late April to early to mid-May depending on farm location and individual flock factors, it says.

The Department says this will decrease the likelihood of clinical disease later and reduce pasture contamination for the next year.

It also says that early lambing flocks where lambs are five to six weeks old and already grazing are particularly vulnerable; as are enterprises with higher stocking rates where lambs are grazing pastures grazed by last year’s lambs.

It advises that veterinary advice should be sought in the event of clinical cases or for a flock control program comprising specific measures for any intensive sheep flock.

It recommended’s that any lambs that die of unknown causes are submitted to a regional veterinary laboratory for post-mortem examination as Nematodirus battus can cause death before clinical signs are apparent.

Benzimidazoles (white drench) and levamisole (yellow drenches) are effective against larval and adult stages of Nematodirus battus, it says

Currently there are no drenches with effective residual activity against Nematodirus which means that as the lamb continues to graze it can become re-infected with larvae again, the Department says.


It is also important that farmers are aware that other parasites cause diarrhoea in young lambs and require different control measures and medication, it says.

The Department says that Nematodirus can be wrongly assumed to be the cause of severe diarrhoea in lambs when in fact the cause is a coccidial infection.

It advises that rotation of pasture and frequent movement of feeding troughs and watering points to drier areas will help prevent coccidiosis in young lambs as localised poaching creates moist conditions suitable for the spread of this parasite..

Both nematodirosis and coccidiosis can occur at the same time in the same lambs, so treatment may need to be targeted at both pathogens, it says.