Nematodirus in lambs
- What is nematodirosis?
- What are the clinical signs of nematodirosis?
- What is the impact of nematodirosis?
- How can I diagnose Nematodirus in my lambs?
- Treatment and prevention of Nematodirus
- When can an infection occur?
Nematodirus is a significant and costly disease of young lambs, often with high mortality rates. Recovered animals will have slower growth rates and parasitic enteritis is thought to cost the UK sheep industry upwards of £84 million annually.1
What is nematodirosis?
Nematodirus is caused by the parasite Nematodirus battus which is widespread in the UK and has a notably different life cycle from other sheep parasites, making it more difficult to predict. Lambs become infected by ingesting eggs shed onto pasture that was grazed by young lambs the previous year.
Nematodirus only affects lambs as ewes have a strong immunity. The parasite develops to its infective form within the egg, which is thick-walled and very resistant to damage. Hatching requires a specific set of environmental conditions, namely freezing, followed by a temperature exceeding 100C for several days. When this occurs, eggs can hatch en masse very quickly, providing a sudden and very high infection challenge. This is known as the ‘spring flush’ and often coincides with lambs becoming more reliant on grazed grass at 6 – 8 weeks old.
What are the clinical signs of nematodirosis?
Clinical signs usually consist of sudden onset, profuse, watery scours, usually affecting multiple animals within the flock. Faecal staining of the fleece is frequently seen, and lambs can be dull, off feed and lose weight rapidly. Death can occur due to dehydration. Weak lambs, multiples and those with concurrent diseases e.g. coccidiosis are often more severely affected. Lambs are sometimes seen staying close to water sources to rehydrate.
What is the impact of nematodirosis?
Mortality rates can be high and up to 5% of the lamb crop may die within days. Alongside the cost of treatment, recovered or less severely affected animals may have severely reduced growth rates and feed conversion efficiency, and may take many more weeks to reach a marketable weight, eroding into profit margins.
How can I diagnose Nematodirus in my lambs?
Worm egg counts are not useful in diagnosing Nematodirus as larvae cause clinical signs before eggs are produced. Faecal worm egg counts (FEWC) are vital post treatment however to ensure it has been successful.
Diagnosis can be made on clinical signs, post-mortem examination and likelihood of disease based on forecasting.
Treatment and prevention of Nematodirus
Treatment with an appropriate Group-1 white drench is usually very effective and is recommended by Sustainable Control of Parasites in Sheep (SCOPS). Appropriate products include Albex 2.5% (albendazole), Bovex (oxfendazole) and Zerofen (fenbendazole).
Treatments are usually given three weeks apart through May and all lambs in a group should be treated. The need for treatment, and timeframes, are highly variable year on year so always check with your vet. Be prepared and keep an appropriate product in stock if a hatch is anticipated as outbreaks can occur very quickly.
To avoid selecting for resistance, it is vital to weigh lambs and dose appropriately. A FEWC should be carried out 7-10 days post-treatment to check for resistance. To prevent disease, do not graze lambs on pasture used for lambs the previous year. If this is unavoidable, pay close attention to parasite forecasts produced by NADIS or SCOPS.
When can an infection occur?
See the below figure for the estimated dates in March and April 2024 when peak nematodirus egg hatching is expected on pasture.
Image Source: https://www.gov.ie/en/press-release/84e15-nematodirus-forecast-2024/
Met Éireann
References:
1. NADIS. PGE in sheep (2024). [Online]. Available from PGE in Sheep | NADIS Forecasts
Nematodirus in lambs
- What is nematodirosis?
- What are the clinical signs of nematodirosis?
- What is the impact of nematodirosis?
- How can I diagnose Nematodirus in my lambs?
- Treatment and prevention of Nematodirus
- When can an infection occur?
Nematodirus is a significant and costly disease of young lambs, often with high mortality rates. Recovered animals will have slower growth rates and parasitic enteritis is thought to cost the UK sheep industry upwards of £84 million annually.1
What is nematodirosis?
Nematodirus is caused by the parasite Nematodirus battus which is widespread in the UK and has a notably different life cycle from other sheep parasites, making it more difficult to predict. Lambs become infected by ingesting eggs shed onto pasture that was grazed by young lambs the previous year.
Nematodirus only affects lambs as ewes have a strong immunity. The parasite develops to its infective form within the egg, which is thick-walled and very resistant to damage. Hatching requires a specific set of environmental conditions, namely freezing, followed by a temperature exceeding 100C for several days. When this occurs, eggs can hatch en masse very quickly, providing a sudden and very high infection challenge. This is known as the ‘spring flush’ and often coincides with lambs becoming more reliant on grazed grass at 6 – 8 weeks old.
What are the clinical signs of nematodirosis?
Clinical signs usually consist of sudden onset, profuse, watery scours, usually affecting multiple animals within the flock. Faecal staining of the fleece is frequently seen, and lambs can be dull, off feed and lose weight rapidly. Death can occur due to dehydration. Weak lambs, multiples and those with concurrent diseases e.g. coccidiosis are often more severely affected. Lambs are sometimes seen staying close to water sources to rehydrate.
What is the impact of nematodirosis?
Mortality rates can be high and up to 5% of the lamb crop may die within days. Alongside the cost of treatment, recovered or less severely affected animals may have severely reduced growth rates and feed conversion efficiency, and may take many more weeks to reach a marketable weight, eroding into profit margins.
How can I diagnose Nematodirus in my lambs?
Worm egg counts are not useful in diagnosing Nematodirus as larvae cause clinical signs before eggs are produced. Faecal worm egg counts (FEWC) are vital post treatment however to ensure it has been successful.
Diagnosis can be made on clinical signs, post-mortem examination and likelihood of disease based on forecasting.
Treatment and prevention of Nematodirus
Treatment with an appropriate Group-1 white drench is usually very effective and is recommended by Sustainable Control of Parasites in Sheep (SCOPS). Appropriate products include Albex 2.5% (albendazole), Bovex (oxfendazole) and Zerofen (fenbendazole).
Treatments are usually given three weeks apart through May and all lambs in a group should be treated. The need for treatment, and timeframes, are highly variable year on year so always check with your vet. Be prepared and keep an appropriate product in stock if a hatch is anticipated as outbreaks can occur very quickly.
To avoid selecting for resistance, it is vital to weigh lambs and dose appropriately. A FEWC should be carried out 7-10 days post-treatment to check for resistance. To prevent disease, do not graze lambs on pasture used for lambs the previous year. If this is unavoidable, pay close attention to parasite forecasts produced by NADIS or SCOPS.
References:
1. NADIS. PGE in sheep (2024). [Online]. Available from PGE in Sheep | NADIS Forecasts