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14 April 2023

Nematodirus is a tricky worm to guard young lambs against, because the level of risk is strongly linked to weather patterns, warns the Sustainable Control of Parasites in Sheep (SCOPS) Group.

So far, spring 2023 has seen variable temperatures, with unseasonably cool spells followed by warmer periods. This means farmers need to understand the risks to their lambs.

The free online SCOPS Nematodirus Forecast helps farmers, vets and advisers predict the risk to individual flocks via a traffic light system that is updated daily using data from 140 weather stations. Users can select their nearest or most representative weather station to quickly check the level of risk, and access advice on higher levels of risk for lower lying ground and/or south-facing slopes. There is also a wider risk assessment and information on treatment options and possible management actions.

Nematodirus battus, the parasite that causes nematodirosis, is unusual because eggs dropped by lambs in the spring overwinter on ground grazed by sheep but don’t hatch until the following spring once temperatures exceed 10°C. Young lambs that are starting to graze and have no immunity to these worms are susceptible to disease, particularly if there is a sudden increase in temperatures causing a mass hatch of the nematodirus eggs. This can have devastating consequences for lambs that are six to 12 weeks of age.

Dr Fiona Lovatt of Flock Health is one of many vets who uses the free service. She says: “The SCOPS Nematodirus Forecast is invaluable for knowing when to act for individual flocks. I like to keep an eye on the stations closest to a farm and track them from week to week as they turn yellow (low risk) and then orange (moderate risk). The stations almost always have a week at red (high risk) before they turn black (very high risk), so we can be ready to time treatments precisely and not be faced with deaths due to untreated vulnerable lambs in high risk fields.”

Amy Griffiths, a Suitably Qualified Person (SQP) working for Mole County Stores, travels extensively in the Derbyshire and Staffordshire area. She says: “Being on the road and visiting a variety of different areas, it is good to have information readily available in an easy-to-understand format. It means I’m equipped with up-to-date knowledge and can give the best advice to my farmer customers.”

Zoe Wall, an SQP based in Devon, would like to see more farmers use the forecast. She says: “It’s the first tool I signpost my customers to when discussing nematodirus. It provides up-to-date and relevant information that can help ensure farmers are worming at the right time, saving themselves time and money, as well as increasing welfare and productivity on the farm.”

The SCOPS Nematodirus Forecast is a free resource for the UK sheep sector, thanks to the generous sponsorship of Bimeda and Techion (FECPAKG2). Visit

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