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.