Treating Nematodirus in lambs at current time

THE vast majority of mid season lambing flocks will at this stage be finished lambing, and later-lambing flocks will be nearing the end of lambing also.

For hill flocks that started lambing in the first week of April, most will be half way through lambing now.

For the earlier mid-season lambing flocks, one parasite that can start to show up around now is Nematodirus.

Nematodirosis is a severe parasitic disease of lambs six to 12 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.

Farms with high stocking rates are particularly vulnerable.

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.

Across the country, Nematodirus egg hatching was expected to peak this year between April 14 and 21, which is a few days later than would normally be expected.

This is due to the recent cooler-than-normal soil temperatures.

At-risk lambs – which are lambs that are typically six to 12 weeks of age and grazing on contaminated pasture or pastures that are repeatedly grazed with sheep and lambs year after year – should be treated approximately two weeks after the peak of egg hatching.

Consideration should be given to dosing lambs earlier on individual farms where clinical signs consistent with Nematodirus are observed.

What wormer should you use? Benzimidazoles (white drenches) are the treatment of choice for Nematodirus infections and are effective against both larval and adult stages.

A white wormer as the firstchoice treatment option will also help to reduce the exposure of other worms at a point in the grazing season when treatment for these may not be necessary.

This will help to sustain the effectiveness of these drugs and reduce the occurrence of resistance to wormers also.

An important point to note is that currently there are no drenches with effective residual activity against Nematodirus.

This means that, as lambs continue to graze, they can become re-infected with larvae, and as a result may require repeated treatments with the same or similar wormers at two to three-week intervals.

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

Nematodirus can be wrongly assumed to be the cause of severe diarrhoea in lambs when, in fact, the cause could be a coccidial infection.

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 coccidia.

Raising feeding troughs will also help to reduce the contamination of feed with faeces and, hence, transmission of coccidiosis.

In some cases, nematodirosis and coccidiosis can occur together, giving rise to severe disease.

Make sure that you keep a close eye on lambs that are within this six-to-12-week age bracket from now on.

And if you see any sign of scouring, dose quickly with an appropriate wormer and, if possible, keep lambs moving to clean pasture.