Sheep farmers must be on guard against nematodirus as a stark contrast between day and night time temperatures could see a mass hatch of over-wintered parasites. This is according to independent sheep consultant Paul Roger who says this year could see an “explosive development of eggs” because of the hard winter.



“Nematodirus eggs require an extended period of cold exposure followed by warmer temperatures above 10C in order to hatch out and this cold winter means many eggs may have survived.”

This supports the NADIS March parasite forecast which says low December and January mean UK temperatures give an early indication that this year may be a high-risk year for nematodirus.

With nematodirus affecting grazing lambs from six weeks old and with potential problems occurring as early as next month as temperatures begin to rise above 10C, farmers need to be conducting risk assessments now, says Mr Roger.

“The main risk factors farmers should consider are weather – a sudden cold snap followed by a period with temperatures above 10C, lambs grazing pasture that carried lambs the previous spring and group’s where there is likely to be a challenge from coccidiosis.”

He says arrangements should be made to minimise the risk factors by grazing animals on pasture that didn’t carry pre-weaning lambs last year or using prophylactic treatments during the risk period, which could be as early as April but in most cases early May to June.

Farmers can not afford to have a “wait and see policy”, stresses ADAS sheep consultant Kate Philips. “Any farm that has had a problem in the past must be vigilant. Nematodirus can take hold so quickly it means farmers must keep on top of it. When farmers feel their lambs are at risk and they need to treat for nematodirus then use a preventative wormer.”

Advice from the Sustainable Control of Parasites group (SCOPs) is to use a white (BZ) drench, which is effective against nematodirus and suitable for young lambs, says Ms Philips. “There is no known resistance to BZs in this species of worm, which means they can be used even where BZ resistance in other worms is confirmed. This can also help reduce the selection pressure put on the other two groups of wormers.”

Mr Roger says intensively-managed flocks should also be on alert for nematodirus, with more cases being reported in these flocks. “Nematodirus is increasingly a problem in intensively-managed flocks, particularly where coccidiosis is a problem. Symptoms include scouring, loss of appetite and rapid weight loss.”

Problems associated with nematodirus are often long-term, adds Mr Roger. “This is because coccidiosis and nematodirus act in the same part of the gut and, when not treated early enough, the finger-link productions used for absorption become stumps, so surface area for the absorption of nutrients is significantly reduced. This means growth rates are hindered and damage is often long-term.”