The Department of Agriculture, Food and the Marine (DAFM) has today (Thursday, April 6) published its nematodirus forecast for 2023.
The maximum egg hatching is expected to peak this year from the end of March to the early days of April in the south and Atlantic coastal fringes.
In the east, midlands and inland areas of the northwest it will be slightly later, with peak egg hatching generally occurring from April 6-12.
Each spring, the department, in collaboration with Met Éireann, University College Dublin (UCD) and Teagasc advises farmers of the predicted risk of disease, chiefly in lambs, caused by the roundworm.
Nematodirus
Nematodirosis is a severe parasitic disease of lambs six to twelve weeks of age which become infected by ingesting large numbers of infective larvae from grazing on contaminated pasture.
The life cycle of Nematodirus battus is unlike that of other roundworms in that 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. Disease typically occurs in April, May and June.
After ingestion by lambs, nematodirus larvae invade the wall of the intestine.
The disease is characterised by profuse diarrhoea, dehydration and weight loss. Calves may also be similarly affected.
In outbreak scenarios, lambs can be seen congregating around water troughs due to the severe thirst that develops.
Adult sheep are unaffected by the parasite.
Prevention
According to the department, the 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, DAFM noted.
Twin lambs or single lambs born to ewes of 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” pasture is available, preference should be given to moving these lambs first.
The DAFM advises farmers that at-risk lambs (typically 6 to 12 weeks of age and grazing on contaminated pasture) should be treated approximately two weeks after the peak of nematodirus egg hatching.
However, consideration should be given to dosing lambs earlier on individual farms where clinical signs consistent with the disease are observed, as the above treatment guidelines are based on estimated peak hatching of eggs
Wormer
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.
The department said that 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.
There are currently 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.
Farmers are reminded that other parasites can also 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 is a coccidial infection.
Rotation of pasture and frequent movement of feeding troughs 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
Veterinary advice
The department said that it is advisable for farmers to consult a private veterinary practitioner for an accurate diagnosis and advice on appropriate medication when lambs with severe diarrhoea and straining are observed.
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, treatment may need to be directed against both pathogens.
It is recommended that any lambs that die unexpectedly are referred to a regional veterinary laboratory for post-mortem examination as N. battus can cause death before clinical signs become apparent.