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Spring Timing Impacts Nematodirus Threat to Lambs

10 April 2015

ANALYSIS – An early spring generally means later lambing flocks escape the parasite challenge of nematodirus, says the latest NADIS parasite forecast.

This is because larvae will have already died by the time these lambs are put to pasture, explains veterinarian Peers Davies, noting how temperatures had risen across the entire UK through March.

Lambs between four and 12 weeks of age tend to be at the greatest risk from grazing pastures, although Mr Davies stressed the effect that lambing timings and the arrival of spring can have on nematodirus risk.

He said this year’s larvae will hatch from eggs produced last year, making the parasite “unusual”.

Temperatures of over 10 degrees cause egg hatching and a “dramatic peak of pasture infectivity”.

“In a year when spring is very late and temperatures don’t increase before late April/May the early lambing flocks will have largely escaped the risk period,” said Mr Davies.

“Flocks that will be hit will be March/early April lambing flocks where lambs will be in the risk period at around four to six weeks old.”

But he added that an early spring often activates larvae sooner, meaning the parasites are dead by the time late lambing flocks have lambs on pasture.

"Early observations suggest that late January and February-born lambs grazing contaminated pastures in the south west of England may need prophylactic anthelmintic drenching before the end of March," Mr Davies advised. 

As a means of prevention, farmers should rotate spring grazing to avoid the larval peak.

These fields, grazed by lambs last year, are now infected and rotation should be used to avoid this where possible.

Medicine cabinets should include Benzimadazole as a “white drench” anthelmintic product. Some instances may require more than one treatment, lamb size and weather depending, added Mr Davies.

He warned that use should be curbed if possible to limit the rate of resistance to anthelmintics that farmers have available to them. When worming ewes at lambing, he noted the trade-off between combatting nematodirus and resistance.

Summing up worming in general he said: “Just treat the ewes that actually need it, this is predominantly young, thin or triplet bearing ewes that are under a great deal of pressure.

And in terms of nematodirus, he added: “Most appropriate control measure is to drench all lambs with a Benzimadazole or white drench as this will kill the parasite very successfully and avoid exposing other worm species to an unnecessary selection pressure.”

Faecal egg counts of several lambs should be checked 10 days after for Teladorsagia infection. 

"Where present, this would likely necessitate an anthelmintic from another class," advised Mr Davies.

Picture courtesy of National Animal Disease Information Service (NADIS) 

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