Nematodirus is a disease caused by gastrointestinal worms which young lambs ingest through grazing, particularly on pasture grazed by young lambs the previous year. It can cause a high number of deaths within a matter of hours and poor growth rates.
This Q&A guide offers answers to common questions surrounding this disease including how to prevent it, how to quickly spot affected lambs, and how to treat them effectively.
What age are lambs most at risk of nematodirus?
Six to twelve week old lambs are most likely to be affected as they are likely to be eating enough grass that could be infected with the worm larvae to put them at risk.
Younger lambs can also be affected if they’re not receiving enough milk which causes them to start grazing earlier, for example, triplets. Those with a weakened immune system, or already presented with other challenges such as coccidiosis, are also more at risk of succumbing to the disease.
From three months-old, lambs are less likely to be affected when they ingest significant numbers of larvae.
What time of year is nematodirus an issue?
A sudden cold snap that’s followed by a period of warm weather (10°C or higher) can trigger a mass hatch of eggs into larvae that are ingested by the lambs, causing their likelihood of exposure to significantly increase. Lambs are therefore most at risk of becoming infected between April and June due to the colder nights and warmer days that typically occur.
Although generally more of an issue in spring, unpredictable weather patterns experienced in recent years have caused nematodirus challenges to occur as early as February.
What are the signs of nematodirus?
Knowing the symptoms of affected lambs will ensure prompt treatment can be administered quickly. These signs include:
- Sudden onset of profuse diarrhoea
- Dark or black faeces
- Dull lambs
- Lambs that stop sucking
- Loss of body condition
How should I prevent nematodirus?
Prevention is better than cure because nematodirus strikes quickly. Faecal egg counts aren’t an effective preventative method because the damage is caused by larvae that don’t produce eggs, however, knowing the signs and taking the following steps will help to reduce the impact of nematodirus:
- Where possible avoid grazing lambs in fields that were grazed by lambs the previous spring
- Nematodirus risk varies year on year so keep an eye on the SCOPS nematodirus forecast to predict the likelihood of your flock being affected and for recommended treatment decisions to help reduce the risk of wormer resistance. This useful tool takes data from weather stations across the UK to provide updates on the disease risk level across the UK based on the predicted hatch-date of eggs into larvae
- Don’t forget your on-farm or in-store specialist can help provide guidance on how to prevent nematodirus, so make sure you get in touch if required
How should I treat nematodirus?
An effective parasite treatment strategy should be part of a flock health plan that should be put in place by a vet as a priority, and will help to make sure nematodirus is treated at the right time, using the right product.
Taking the following steps when managing nematodirus will also help to prevent wormer resistance, one of the biggest health risks to UK sheep farming at the moment:
- If just one lamb shows symptoms of nematodirus, treat every lamb within the group as quickly as possible using a white (1-BZ) drench
- It’s extremely important to dose for the correct weight of the lamb – follow the product guidance for correct dosing measures
- Conduct a faecal egg count seven to ten days after the drench is administered to ensure treatment is effective. Ensure all groups of lambs are tested separately because the level of infestation will vary between fields. Interpretation of the FEC is complex, so it’s best to discuss this and any next steps with your vet
- Severely affected lambs may require further treatment which your vet will be able to advise on
- Consult your vet if you’re unsure as to how to treat lambs