While the wet weather in early spring made lambing harder work than usual, it also reduced the nematodirus threat to 2024-born lambs.

This is according to the Sustainable Control of Parasites in Sheep (SCOPS) group. The SCOPS Nematodirus Forecast indicates a lower risk of nematodirus for lambs born this year.

Speaking on behalf of SCOPS, Moredun scientist Dr Dave Bartley said:

“Nematodirus roundworms causes huge problems when a sudden hatch of nematodirus eggs (triggered by a sudden increase in temperature after a cold spell) coincides with when young lambs start to drink less milk and take in lots of grazed grass instead.

“The weather in early spring this year means the hatch has been very gradual and many lambs have been able to build up natural immunity to nematodirus without needing to be treated.

“Anecdotal reports made to SCOPS suggest fewer lambs have been treated for nematodirus this spring, which means producers have been able to save time and money, and also preserve the efficacy of white wormers.”


White wormers (group 1-BZ) are still largely effective against the nematodirus roundworm, despite there being widespread resistance to these products in other roundworm species, SCOPS said

Dr Bartley said continued use of white wormers will reduce this efficacy over time, but reducing exposure will delay this for as long as possible.

“The colour coding on the SCOPS Nematodirus Forecast map allows farmers, vets and advisers to check on when the high risk period is for their flock and act accordingly, and it’s great to see and hear that people have been using the free service again this year, rather than assuming it is a low-risk year or, conversely, assuming they should just treat lambs at the same time as they have in previous years,” he said.

Image: SCOPS Nematodirus Forecast 

Rudolf Reichel of the Animal & Plant Health Agency (APHA) said the nematodirus risk is not quite over for 2024 and urges farmers with later-born lambs in upland and/or northern areas of the UK to keep an eye on the SCOPS Nematodirus Forecast.

“If the spot closest to you on the forecast map is only just turning red (high risk) or black (very high risk) then you need to be aware of the risk to younger lambs,” he said.

“If your spot is orange (moderate risk) or yellow (low risk) and you’re not sure if on its ways towards turning red/black or on its way back from having already been red/black, use the ‘Historic Data’ tab on the website to check.”

Faecal egg counts

Rebecca Mearns of Biobest said it is a busy time in terms of returning faecal egg count (FEC) test results to farmers, vets and advisers.

Mearns said she is aware that some of these are showing nematodirus eggs and is keen to emphasis this does not necessarily indicate a need to treat lambs.

“Regular FECs are an invaluable tool for sheep farmers but, at this time of year, seeing nematodirus on the results sheet can be confusing,” she said.

“Because of the different lifecycle of this worm compared to other roundworms, by the time we’re detecting nematodirus eggs in FECs it’s may be too late, as disease in lambs is caused by the immature larvae stages, so before eggs are detectable.

“Depending on individual circumstance, where you see nematodirus eggs in FECs, lambs may have already succumbed to disease or may be beyond the risk period and will have picked up natural immunity.”

Mearns said this does not mean that farmers should completely ignore the information, as it is “really useful” to understand the number of nematodirus eggs that are likely to overwinter later this year and pose a threat to lambs born in 2025.

“Picking up trends on which fields have the heaviest burden will help you make informed decisions next lambing time,” she said.