Sheep farmers should consider five key factors to gauge nematodirus risk on their holding as the threat of the disease rises across the country, warn livestock advisers.
This follows disease monitoring updates from across the country, with 29 of 140 weather stations currently at “high risk” or “very high risk”.
The 29 forecasts are mainly across central and southern England and Wales, but also appear as far north as the Vale of York and Strathallen, Scotland.
This represents a danger to lambs, both through lost growth performance and potential mortality, says the Sustainable Control of Parasites in Sheep (Scops) group
Many weather stations at higher altitudes and further north and west remain at “negligible” or “low risk”. Farmers should look for risk level at the nearest weather station data by checking the nematodirus forecast.
Scops says the first factor to assess is if lambs are on high-risk pasture – for example, pasture that was grazed by ewes and lambs last spring.
If one or more of the following four factors is present on their holding, farmers are advised to act now (see “Advice on nematodirus”).
- Are lambs old enough to be eating significant amounts of grass? This is generally from six to 12 weeks of age, but can be younger if ewes are not milking well
- Do you have groups likely to have a coccidiosis challenge? For example, mixed age lambs are at highest risk
- Has there been a sudden cold snap followed by warm weather?
- Are lambs under other stresses. For example, triplets, fostered lambs or lambs on young or old ewes.
Advice on nematodirus
Why is nematodirus such a problem?
- The Nematodirus battus worm has a different lifecycle than other sheep worms – the infective larvae develop inside the egg and infection passes from one lamb crop to the next year’s crop
- Cold weather delays hatching and a sudden change in temperature of 10C or more can result in a mass hatch
How to act against nematodirus
- Move at-risk lambs can be moved to low-risk, clean pastures that were not grazed by lambs the previous spring
- If lambs cannot be moved from high-risk pastures, consider treating with a benzimidazole drench
- These drenches are still widely effective, although some resistance in Nematodirus battus was confirmed in 2011
- Check which benzimidazole drench is available via the Scops ‘Know your anthelmintics guide’
- 10 days after treatment, check whether it was effective by carrying out a faecal egg count
- It may then be necessary to treat lambs again, depending on subsequent weather and the ages of lambs
See also: How to control gastrointestinal parasites in sheep and cattle for more on nematodirus