17 Aug 2022

Earlier than usual - Nematodirus Forecast for Kilkenny farmers

Kilkenny Kilkenny Kilkenny

Kilkenny farmers are being warned by the Department of Agriculture that this year's Nematodirus disease warning is earlier than usual.

According to the Department, this year Nematodirus larval hatching is expected to peak between March 23rd and April  13th which is about one week earlier than would normally be expected. This is due to milder  than normal soil temperatures.  

The majority of the country will see maximum larval hatching in the week of the 5th to the  10th of April with the exception of the south-western coastal region where the peak is  expected to occur between late March and the first days of April, and coastal fringes of the  west and northwest where it is expected in the first few days of April.  

When should lambs be treated? 

At-risk lambs (i.e. typically 6 – 12 weeks of age and grazing on contaminated pasture) should be treated approximately two weeks after the peak of egg hatching. 

Along the south west coast, as well as coastal fringes of the west and northwest, lambs should  be dosed with a suitable wormer (anthelmintic) by the second week of April while lambs in  the rest of the country should be dosed in the last two weeks of April. 

However, consideration should be given to dosing lambs earlier on individual farms where  clinical signs consistent with Nematodirus are observed as the above treatment guidelines are  based on estimated peak hatch of eggs.

What wormer should be used? 

  • Benzimidazoles (white drenches) are the treatment of choice for Nematodirus infections and  are effective against both larval and adult stages. The use of this anthelmintic class as the first-choice treatment option will also help to reduce the exposure of other worms such as  Trichostrongylus and Teladorsagia to other anthelmintic classes (e.g. macrocyclic lactones)  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 is particularly important on farms with pre existing issues of benzimidazole resistance in populations of the common stomach/intestinal  roundworms. 

Please note 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 throughout the spring.


This disease is best prevented by keeping the current year’s lambs off any 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.

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