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Catherina Cunnane
Catherina Cunnane
Catherina Cunnane hails from a sixth-generation drystock and specialised pedigree suckler enterprise in Co. Mayo. She currently holds the positions of editor and general manager at That's Farming, having joined the firm during its start-up phase in 2015.
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Nematodirus: The signs, when it will peak and how to prevent

2022 Nematodirus Forecast for Ireland 

The Department of Agriculture, Food and the Marine has published its 2022 Nematodirus forecast.

Each spring, in collaboration with Met Éireann, UCD and Teagasc, the DAFM advises farmers of the predicted risk of disease, chiefly in lambs, which the roundworm Nematodirus battus, causes.

Nematodirosis is a “severe” parasitic disease of lambs 6 to 12-weeks of age. They become infected by ingesting large numbers of infective larvae from grazing on contaminated pasture.

According to the forecast, the life cycle of N. battus, is unlike that of other roundworms. Eggs deposited on pasture do not hatch until the following year to release the infective larvae.

This happens during a mass hatching event in spring when soil temperatures increase after a period of cold weather. There, the forecast adds that the disease typically occurs in April, May and June.

After ingestion by lambs, Nematodirus larvae invade the wall of the intestine. Infection is characterised by:

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  • Profuse diarrhoea;
  • Dehydration;
  • Weight loss.

In outbreak scenarios, you can see lambs congregating around water troughs due to the severe thirst that develops. The bodies confirmed the parasite does not impact adult sheep.

How to prevent the disease

You can prevent the disease by keeping the current year’s lambs off any pasture lambs, or young calves (which can be carriers of infection) grazed in the previous year. Farms with high stocking rates are particularly vulnerable.

According to the forecast, twin lambs or single lambs born to ewes with poor milking ability may be at a greater risk of developing the disease as they begin consuming greater amounts of grass earlier in life.

If clean, ungrazed pasture is available, you should give preference to moving these lambs first.

When will the disease occur in 2022?

This year, the bodies expect the maximum Nematodirus egg hatching to peak between April 6th and 18th.

They say this is close to the normal period for egg hatching due to the March 2022 average values being close to the long-term average of soil temperatures.

They say most of the country will see maximum egg hatching around the second and third weeks of April.

This is except for the coastal fringes along the south, west and northwest coast, which will be earlier, with the DAFM expecting the peak in egg hatching at the end of March and in the early days of April.

When should you treat lambs?

The bodies advise farmers to treat at-risk lambs (i.e., typically six to 12 weeks of age and grazing on contaminated pasture) approximately two weeks after the peak of Nematodirus egg hatching.

However, you should consider dosing lambs earlier on individual farms where you observe clinical signs consistent with Nematodirus, as the bodies have placed the above treatment guidelines on estimated peak hatching of eggs.

Source: Met Éireann
What wormer should I use? 

Use a suitable wormer. According to the DAFM, 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.

As a result, they may require repeated treatments with the same or similar wormers at two to three-week intervals throughout the spring.

Nematodirus and coccidiosis in lambs

It is also important to stress that other parasites can also cause diarrhoea in young lambs which require different control measures and medication.

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

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

Veterinary advice and laboratory diagnostic aids

Consult a private veterinary practitioner for an accurate diagnosis and advice on appropriate medication when you observe lambs with severe diarrhoea and straining.

This is especially the case where there has been little or no improvement from an initial worming treatment. As both nematodirosis and coccidiosis can occur at the same time, you may need to direct treatment against both pathogens.

The DAFM recommends that any lambs that die unexpectedly are referred to a private veterinary practitioner to a regional veterinary laboratory for post-mortem examination as N. battus can cause death before clinical signs become apparent.

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