Focus on winter worms in sheep
- What worms can cause disease in winter?
- Is my farm at risk?
- Treating winter worms
- Looking ahead
Gut worms, including Trichostrongylus, Telodorsagia and Haemonchus, can be the cause of scouring and/or poor growth in lambs and sheep late in the season. This occurs when sheep graze infective pasture in the autumn and winter and ingest a large number of worm larvae.
As our autumns and winters become warmer, these winter worms are likely to become an increasingly significant problem, especially for out-wintered lambs grazing pasture.
What worms can cause disease in winter?
Gut worms, including Trichostrongylus, Telodorsagia and Haemonchus.
Adult female worms inside the sheep will lay eggs which will be excreted in sheep muck. Each egg will then release a first-stage larva (L1) which cannot infect sheep again until it has developed to become an infective third-stage larva (L3). These L3 larvae will migrate onto the herbage where they will be eaten by sheep. Once ingested these larvae will once again develop and then emerge as adult worms which will start producing eggs. Adult worms will typically live up to 12 weeks within the sheep if they have not been killed by either the immune system of the individual or by anthelmintics administered.
Rainfall records, along with the time of year, can be used to predict peak levels of nematode larvae on the pasture available to stock. Larvae from eggs deposited in early spring could take 10-12 weeks to develop, however eggs deposited in summer will only take 1-2 weeks and therefore they will both reach the infective stage at about the same time. This can then lead to high levels of pasture infectivity from mid-summer onwards.
When determining the worm risk to sheep we classify pasture as:
• Clean – no sheep worm eggs or larvae are present. This is rare in sheep farms it requires either 2 years of no sheep grazing or a year of no grazing followed by a full reseed.1
• Contaminated – eggs and larvae are present on the pasture, meaning this pasture will be a risk to sheep in future.
• Infective – the infective L3 stage are present on the pasture AND conditions (rainfall and temperature) stimulate them to migrate up the herbage allowing them to be eaten. This pasture is currently a risk to sheep.
L3 larvae are most active during warm weather and will die if not consumed relatively quickly due to using up their energy store. During autumn and winter L3 may survive longer and even over-winter on pasture. Climatic changes which have resulted in warmer, wetter winters means that the L3 on pasture in autumn and winter are becoming a more significant source of infection the following spring. Although these over-wintering L3 are a source of infection to sheep grazing late winter and early spring they don’t survive long on pastures once ambient temperatures rise. Late April/early May tends to have the lowest levels of pasture infectivity. A high level of pasture infectivity in late summer and autumn is due to the deposition of eggs in spring and early summer.
Haemonchus contortus worms can produce up to 10,000 eggs per day and when combined with warm and wet conditions (usually between mid-spring and late autumn) which allow rapid development of eggs to L3, pastures can become highly infective extremely quickly. This means that there can be serious, unexpected haemonchosis outbreaks in both ewes and lambs from pasture infectivity changing from low in early spring to very high in summer and autumn.
These worm populations are also capable of arresting their development at the L4 stage and remain dormant for long periods (hypobiosis). Hypobiosis usually occurs in the larvae that are ingested in the late autumn and winter, and they can then resume their development into egg-laying adults the following spring.
The impact of hypobiosis:
- When Teladorsagia hypobiotic larvae resume development, they can cause disease in yearling sheep.
- Worms that have developed from hypobiotic larvae in ewes are an important source of pasture contamination in the spring and early summer.
- Hypobiosis is the main way H.contortus survives the winter.
Is my farm at risk?
Parasite forecasts can be a useful tool to help you predict if gut worms are likely to be a significant problem in your area, according to the climate. A combination of methods used in conjunction are important to aid the diagnosis of nematode infestations. Faecal egg counts (FECs), clinical signs, regular (ideally weekly) weighing to monitor growth weights, grazing history, and post-mortem examinations (PMs) can all be useful tools to help you decide whether a treatment is needed. Reduced growth rates are likely to be the first indication your lambs may be affected by worms. Gut worms and poorer grass quality in the autumn/winter make grazing lambs at this time of year challenging.
It is useful to keep a diary of FEC results for different groups and if required what treatments are given and when, alongside pasture mapping in a bid to identify high-risk grazing.
Treating winter worms
If growth rates are slowing, there is a significant worm egg count and/or lamb condition is deteriorating, you are likely to need to worm your lambs. The product you choose will depend on what wormers are effective on your farm. Studies have shown that wormer resistance can vary between seasons on a farm.2 Therefore, it is imperative that you use post drench (7 days post levamisole and 14 days post all other wormer treatments) worm egg counts to determine the efficacy of the treatment you have used.3 You should check this after every treatment, as worms present in the autumn/winter are likely to be different to the summer.
If Haemonchus is diagnosed, the treatment choice should be discussed with a vet. Haemonchus has been shown to be among the first worms to develop resistance, and therefore treatment choice is critical.
Animec or Moxodex would be effective against gut worms and inhibited larvae. Chanaverm may be effective, but will not treat inhibited larvae. Albex should be used with caution though as there are very high levels of resistance reported to the active albendazole.2 Tribamec Duo may be an option if fluke has also been diagnosed, or there is a high risk of fluke and ivermectin is effective on your farm. Read more about fluke .
Looking ahead - have you started to think about next year?
If worms have been a significant problem in the autumn/winter, you need to look ahead to next year to reduce pasture burdens and graze high-risk stock i.e. lambs on the lowest-risk pastures. Read more about treating ewes around lambing to reduce pasture contamination and pasture management for worm control.
References:
1. https://www.teagasc.ie/news--events/daily/sheep/understanding-pasture-contamination-and-its-implications-for-management-1.php#:~:text=Cleaner%20pasture&text=It%20was%20only%20occasionally%20grazed,on%20this%20pasture%20is%20low
2. WAARD Project Final Report. Sept 2015
3. SCOPS A Users Guide to the Sheep Worming Treatment Check
Focus on winter worms in sheep
- What worms can cause disease in winter?
- Is my farm at risk?
- Treating winter worms
- Looking ahead
Gut worms, including Trichostrongylus, Telodorsagia and Haemonchus, can be the cause of scouring and/or poor growth in lambs and sheep late in the season. This occurs when sheep graze infective pasture in the autumn and winter and ingest a large number of worm larvae.
As our autumns and winters become warmer, these winter worms are likely to become an increasingly significant problem, especially for out-wintered lambs grazing pasture.
What worms can cause disease in winter?
Gut worms, including Trichostrongylus, Telodorsagia and Haemonchus.
Adult female worms inside the sheep will lay eggs which will be excreted in sheep muck. Each egg will then release a first-stage larva (L1) which cannot infect sheep again until it has developed to become an infective third-stage larva (L3). These L3 larvae will migrate onto the herbage where they will be eaten by sheep. Once ingested these larvae will once again develop and then emerge as adult worms which will start producing eggs. Adult worms will typically live up to 12 weeks within the sheep if they have not been killed by either the immune system of the individual or by anthelmintics administered.
Rainfall records, along with the time of year, can be used to predict peak levels of nematode larvae on the pasture available to stock. Larvae from eggs deposited in early spring could take 10-12 weeks to develop, however eggs deposited in summer will only take 1-2 weeks and therefore they will both reach the infective stage at about the same time. This can then lead to high levels of pasture infectivity from mid-summer onwards.
When determining the worm risk to sheep we classify pasture as:
• Clean – no sheep worm eggs or larvae are present. This is rare in sheep farms it requires either 2 years of no sheep grazing or a year of no grazing followed by a full reseed.1
• Contaminated – eggs and larvae are present on the pasture, meaning this pasture will be a risk to sheep in future.
• Infective – the infective L3 stage are present on the pasture AND conditions (rainfall and temperature) stimulate them to migrate up the herbage allowing them to be eaten. This pasture is currently a risk to sheep.
L3 larvae are most active during warm weather and will die if not consumed relatively quickly due to using up their energy store. During autumn and winter L3 may survive longer and even over-winter on pasture. Climatic changes which have resulted in warmer, wetter winters means that the L3 on pasture in autumn and winter are becoming a more significant source of infection the following spring. Although these over-wintering L3 are a source of infection to sheep grazing late winter and early spring they don’t survive long on pastures once ambient temperatures rise. Late April/early May tends to have the lowest levels of pasture infectivity. A high level of pasture infectivity in late summer and autumn is due to the deposition of eggs in spring and early summer.
Haemonchus contortus worms can produce up to 10,000 eggs per day and when combined with warm and wet conditions (usually between mid-spring and late autumn) which allow rapid development of eggs to L3, pastures can become highly infective extremely quickly. This means that there can be serious, unexpected haemonchosis outbreaks in both ewes and lambs from pasture infectivity changing from low in early spring to very high in summer and autumn.
These worm populations are also capable of arresting their development at the L4 stage and remain dormant for long periods (hypobiosis). Hypobiosis usually occurs in the larvae that are ingested in the late autumn and winter, and they can then resume their development into egg-laying adults the following spring.
The impact of hypobiosis:
- When Teladorsagia hypobiotic larvae resume development, they can cause disease in yearling sheep.
- Worms that have developed from hypobiotic larvae in ewes are an important source of pasture contamination in the spring and early summer.
- Hypobiosis is the main way H.contortus survives the winter.
Is my farm at risk?
Parasite forecasts can be a useful tool to help you predict if gut worms are likely to be a significant problem in your area, according to the climate. A combination of methods used in conjunction are important to aid the diagnosis of nematode infestations. Faecal egg counts (FECs), clinical signs, regular (ideally weekly) weighing to monitor growth weights, grazing history, and post-mortem examinations (PMs) can all be useful tools to help you decide whether a treatment is needed. Reduced growth rates are likely to be the first indication your lambs may be affected by worms. Gut worms and poorer grass quality in the autumn/winter make grazing lambs at this time of year challenging.
It is useful to keep a diary of FEC results for different groups and if required what treatments are given and when, alongside pasture mapping in a bid to identify high-risk grazing.
Treating winter worms
If growth rates are slowing, there is a significant worm egg count and/or lamb condition is deteriorating, you are likely to need to worm your lambs. The product you choose will depend on what wormers are effective on your farm. Studies have shown that wormer resistance can vary between seasons on a farm.2 Therefore, it is imperative that you use post drench (7 days post levamisole and 14 days post all other wormer treatments) worm egg counts to determine the efficacy of the treatment you have used.3 You should check this after every treatment, as worms present in the autumn/winter are likely to be different to the summer.
If Haemonchus is diagnosed, the treatment choice should be discussed with a vet. Haemonchus has been shown to be among the first worms to develop resistance, and therefore treatment choice is critical.
Animec or Moxodex would be effective against gut worms and inhibited larvae. Chanaverm may be effective, but will not treat inhibited larvae. Albex should be used with caution though as there are very high levels of resistance reported to the active albendazole.2 Tribamec Duo may be an option if fluke has also been diagnosed, or there is a high risk of fluke and ivermectin is effective on your farm. Read more about fluke .
Looking ahead - have you started to think about next year?
If worms have been a significant problem in the autumn/winter, you need to look ahead to next year to reduce pasture burdens and graze high-risk stock i.e. lambs on the lowest-risk pastures. Read more about treating ewes around lambing to reduce pasture contamination and pasture management for worm control.
References:
1. https://www.teagasc.ie/news--events/daily/sheep/understanding-pasture-contamination-and-its-implications-for-management-1.php#:~:text=Cleaner%20pasture&text=It%20was%20only%20occasionally%20grazed,on%20this%20pasture%20is%20low
2. WAARD Project Final Report. Sept 2015
3. SCOPS A Users Guide to the Sheep Worming Treatment Check