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Spring 2011 - Parasitic Disease Forecast

Nematodirosis in lambs:

Nematodirosis is a severe disease of 6-12 week old lambs, which become infected through ingesting large numbers of infected larvae present on contaminated pasture. The life cycle of the Nematodirus battus worm is unusual in that there is a mass hatching of larvae in spring when the soil temperature increases after a period of cold weather. Infection is characterised by profuse diarrhoea and wasting and mortalities in untreated lambs can be high. Nematodirus larvae invade the intestinal mucosa and in some cases death may occur before signs of diarrhoea induced by adult worms are observed. This disease is best prevented by keeping the current year's lambs off pasture that was grazed by lambs last year.

December was one of the coldest months on record and these cold and dry conditions continued in January. Milder, wet weather dominated in February, while a predominance of high-pressure systems in March brought dry and settled conditions. Soil temperatures during March indicate that peak hatching of Nematodirus larvae would occur in most areas of the country during the period 9th to 21st of April. However, in Atlantic coastal areas hatching may have occurred earlier i.e. week of 2nd to 8th April, and lambs may show clinical signs of infection two to three weeks from these dates.

Lambs should be dosed with a suitable anthelmintic in early to mid-May to decrease the likelihood of clinical problems later and also to lower pasture contamination for the next year.  It is especially important, that farmers, with large sheep enterprises and where "safe" pasture is not available i.e. this season's lambs are now grazing pasture where lambs grazed last spring, treat their sheep with an appropriate (narrow spectrum) anthelmintic at this time. When dosing for nematodirosis, farmers should be cognisant of the principals of sustainable control of intestinal parasites and should only use anthelmintics effective against adult worms.

Coccidiosis in lambs:

It is also important that farmers are aware that other parasites cause diarrhoea in young lambs and 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 and watering points to drier areas will help prevent coccidiosis in young lambs as localised poaching creates moist conditions suitable for the spread of this parasite. Raising feeding troughs will also help reduce the contamination of feed with faeces.

It is advisable to consult a private veterinary practitioner for an accurate diagnosis and advice on appropriate medication if lambs with severe diarrhoea and straining are observed. Faecal samples can be submitted to the Central and Regional Veterinary Laboratories for testing. This service is available through private veterinary practitioners and can be used to assess the level of parasite infection on farms and also to assist in the development of parasite control programmes.

Note for editors:

This press release is prepared in conjunction with the Nematodirus Advisory Group. This group comprises representatives from the Department of Agriculture, Fisheries and Food; Teagasc; Met Eireann; University College Dublin and the pharmaceutical industry.

Date Released: 15 April 2011