Sheep farmers: Department predicts risk of infection to lambs

The Department of Agriculture, Food and the Marine has issued advice to farmers in relation to the predicted risk of infection in lambs, based on the advice it has received from the Nematodirus Advisory Group.

According to a statement issued by the department, Nematodirosis is a severe disease of lambs aged six to 12 weeks-of-age who become infected through ingesting large numbers of infective larvae present on contaminated pasture.

The lifecycle of Nematodirus battus is unlike that of other roundworms in that, typically, it takes almost a year before the egg hatches, releasing the infective larva.

There is a mass hatching of larvae in spring when the soil temperature increases after a period of cold weather and disease typically occurs in April, May and June.

After ingestion, Nematodirus larvae invade the intestinal mucosa and infection is characterised by profuse diarrhoea, dehydration and weight loss.

In outbreak scenarios, lambs can be seen congregating around water troughs due to the severe thirst that develops, while the ewes which are unaffected continue to graze.

This disease is best prevented by keeping the current year’s lambs off pasture that was grazed by lambs or young calves in the previous year.

Enterprises with high stocking rates are said to be particularly vulnerable to the attack.

The department outlined 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.

When does it occur?

According to the statement, the maximum Nematodirus larval hatching peaks in the last week of March along the south-west coast and west of Ireland, and into the first two weeks of April for most of the rest of the country.

Lambs may begin to show clinical signs of infection two to three weeks from these dates of peak hatching.

Nationally, soil temperatures are warmer than normal for this time of year, leading to maximum larval hatching occurring two to three weeks earlier than last year.

When should lambs be treated?

Along the south-west coast and west of Ireland, lambs should be dosed with a suitable wormer (anthelmintic) by the second week of April (two weeks after peak larval hatching), while lambs in the rest of the country should be dosed during the third week of April.

Lambs should be treated with benzimidazoles (white drenches) for Nematodirus infections, as these drenches are effective against both larval and adult stages.

According to the department, farmers should 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 at two to three week intervals.

The statement stressed that farmers should be aware that other parasites can cause diarrhoea in young lambs which require different control measures and medication.

Rotation of pasture and frequent movement of feeding troughs and watering points to drier areas were suggested as ideas to help prevent coccidiosis in young lambs, as localised poaching creates moist conditions suitable for the spread of these parasites.

Finally, the statement concluded by noting that raising feeding troughs will also help to reduce the contamination of feed with faeces and hence transmission of coccidiosis.