Weekly Blog
Gut worms in lambs – Diagnosis and treatment of parasitic gastroenteritis (PGE)
Diagnosis of gut worms and the timing oftreatment is an essential cornerstone of successful worm control in sheep. Selecting the most effective wormer is imperative, especially with theincreasing levels of wormer resistance in the UK.
A recent project on farms in Wales showed:1
- 94% of farms had evidence ofworm resistance to Benzimidazole (Group 1 - White group of wormers)
- 68% had resistance toLevamisole (Group 2 - Yellow group of wormers)
- 51% resistance to Ivermectin (Group3 – Clear group of wormers)
- 19% of farms testeddemonstrated evidence of resistance to Moxidectin (also in group 3 – Clear groupof wormers)
A concerning 15% of farms had resistance toall four wormers tested.1
What is parasitic gastroenteritis (PGE) in lambs?
PGE, as the name suggests is a parasiticinfection of lambs’ guts. The disease is mainly a concern in first-season lambs,as healthy adult ewes and rams usually build up a good level of immunity afterexposure to worms in the first year of life. If you purchase ewe lambs oryearlings, these need to be treated as a separate risk group, as they may nothave developed immunity to the worm population on your farm. Homebred yearlings may also be at higher riskas they are under more pressure.
There are four main types of gut worm thatinfect lambs in the UK:
1. Nematodirus can cause a specific disease in very young lambs (see Nematodirus blog) and contributes to PGE for the rest of the season.
2. Ostertagia infects lambs in early summer.
3. Haemonchus can affect lambs or ewes from the summer onwards. This parasite is blood-sucking and usually presents differentlyto the other worms described.
4. Teladorsagia infects lambs in late summer/autumn.
See our clinical signs of PGE blog for a more in-depth look at how these parasites affect lambsand ewes.
When should I worm my lambs?
Traditional set worming programs are becoming less appropriate as awareness of wormer resistance improves. Strategic worming as PGE is starting to cause a problem, but before there are significant health, welfare, and production losses, is the main aim of targeted treatment. There are three main tools in the locker for deciding when wormingis necessary:
1. Faecal worm egg counts(FECs)
The use of FECsis an easy tool to help you decide if animals need worming. The same amount (a teaspoon) of faeces should be collected from at least 10 animals in the groupand tested for the presence of worm eggs. This could be done on farm (if you have the kit), by your vet, or some agricultural merchants will offer theservice. A FEC will give an approximate measure of the severity of the worm burden present in the lambs. A discussion should be had with your vet/SQP/RAMA to discuss results along with your observations of the animals, as describedbelow.
*There are times whereFECs may not be appropriate, e.g. for the diagnosis of Nematodirus, where asignificant worm burden may be present and causing disease without seeing wormeggs in the faeces*.
2. Weight gain
The daily liveweight gain (DLWG) of lambs can be a useful tool to determine if lambs areaffected by a production-limiting disease such as PGE. The key here is to havethe ability to record and compare weight data quickly and easily e.g. with farm software. If your lambs are not growing as quickly as they should, you need to investigate. This tool in conjunction with FECs and observation of the flock’s cleanliness can help form a strategy for treatment.
3. Condition and cleanliness ofthe lambs
Last but certainly not least, you need to monitor your flock carefully for cleanliness of the back end, and condition of the animals. Spending some time assessing the flock visually for cleanliness is always going to be worthwhile, as well as putting your hand on the backs of the lambs to check condition. Again,recording condition will aid you in spotting trends and treating before you’re left with a more serious problem.
Choosing which lambs to worm
Once you have decided which group of lambs/ewes need treating, you then need to decide which animals to treat within the group.
Treating the whole group at once can lead to the acceleration of resistance developing. If all the animals in the group are treated with a wormer at the same time, then all the worms inside those lambs are being exposed to the drug. ONLY worms that are resistant to the wormer will survive the treatment and continue to produce eggs, which are subsequently released onto your pasture. This means that ALL the eggs being released onto your pasture are likely to have the genes that are resistant tothe wormer used.
We know that worms will affect lambs to varying degrees, so some animals that are clean and growing well may not needto be wormed. If you leave some animals in the group (e.g. the best 10%) untreated,you will be leaving a ‘normal’ population (resistant and susceptible) of wormsinside these animals to release a ‘normal’ population of eggs on your pasture. This reduces the selection pressure for resistance. This concept is called leavinga population ‘in refugia’.
Similarly, it is also good practice to send lambs back to their current pasture for 48 hours after worming before moving to ‘fresh’ pasture, to ensure they pick up a ‘normal’ population of worms, ratherthan just taking the resistant population to the new pasture.
Which wormer should I use?
You have decided you need to worm; you havea plan for leaving a worm population in refugia, now you need to decide whichwormer class to use.
There are three main wormer classes youcould use, with the addition of Moxidectin. Moxidectin is part of the Ivermectin, Group 3 wormers, but is classed separately as worms can be susceptible to Moxidectin even if they are resistant to Ivermectin wormers.
1. Group 1 BZ – White drench (Benzimidazoles) – (confusingly, these can also be green, cream, blue in colour) – for example Albex
2. Group 2 LV – Yellow drench(Levamisole) – for example Chanaverm
3. Group 3 ML* – Clear drench (Ivermectin, Doromectin)– for example Animec
a. Group 3 ML* – Clear drench (Moxidectin) – for example Moxodex , long-lasting residua activity for 5 weeks, with a dosing interval of 8 weeks and meat withdrawal of just 14 days
*Also available in injectable form
There are also two ‘newer’ classes of wormer. A quarantine treatment for all incoming animals, with wormer from the newer classes should be considered, in line with SCOPS recommendations and under veterinary or SQP/RAMA guidance. In addition, it has been suggested that one ofthese wormers be given as a one-off treatment for lambs, in the latter part ofthe grazing season. This protocol may slow the development of resistance forwormers in groups 1 to 3.
4. Group 4 AD – ‘Orange’ drench
5. Group 5 SI – ‘Purple’ drench - currently only licensed as a dual active with a 3-ML wormer inthe UK.
Knowing which wormer to use can beconfusing, as a large range of products is available, all with different tradenames. Selecting the right wormer is also very specific to your farm and sheep.
First, you must know which wormer classes are effective on your farm by testing the resistance profile of the worms present. Once you know what is effective, you can devise a strategy with your vet or SQP/RAMA as to which one to use and when. It is important to always use best practice when treating your flock for worms, and the SCOPS manual provides a useful guide for this.
In general, to reduce the chance of resistance, you need to rotate wormer classes within a season to ensure you are not repeatedly exposing worms to the same drug. The Chanelle anthelmintic range includes wormers for sheep across the three main wormer classes to help support responsible worming.
References:
1. WAARD_FINAL_PROJECT_REPORT_1_-_19-11-15.pdf(meatpromotion.wales)
Diagnosis of gut worms and the timing oftreatment is an essential cornerstone of successful worm control in sheep. Selecting the most effective wormer is imperative, especially with theincreasing levels of wormer resistance in the UK.
A recent project on farms in Wales showed:1
- 94% of farms had evidence ofworm resistance to Benzimidazole (Group 1 - White group of wormers)
- 68% had resistance toLevamisole (Group 2 - Yellow group of wormers)
- 51% resistance to Ivermectin (Group3 – Clear group of wormers)
- 19% of farms testeddemonstrated evidence of resistance to Moxidectin (also in group 3 – Clear groupof wormers)
A concerning 15% of farms had resistance toall four wormers tested.1
What is parasitic gastroenteritis (PGE) in lambs?
PGE, as the name suggests is a parasiticinfection of lambs’ guts. The disease is mainly a concern in first-season lambs,as healthy adult ewes and rams usually build up a good level of immunity afterexposure to worms in the first year of life. If you purchase ewe lambs oryearlings, these need to be treated as a separate risk group, as they may nothave developed immunity to the worm population on your farm. Homebred yearlings may also be at higher riskas they are under more pressure.
There are four main types of gut worm thatinfect lambs in the UK:
1. Nematodirus can cause a specific disease in very young lambs (see Nematodirus blog) and contributes to PGE for the rest of the season.
2. Ostertagia infects lambs in early summer.
3. Haemonchus can affect lambs or ewes from the summer onwards. This parasite is blood-sucking and usually presents differentlyto the other worms described.
4. Teladorsagia infects lambs in late summer/autumn.
See our clinical signs of PGE blog for a more in-depth look at how these parasites affect lambsand ewes.
When should I worm my lambs?
Traditional set worming programs are becoming less appropriate as awareness of wormer resistance improves. Strategic worming as PGE is starting to cause a problem, but before there are significant health, welfare, and production losses, is the main aim of targeted treatment. There are three main tools in the locker for deciding when wormingis necessary:
1. Faecal worm egg counts(FECs)
The use of FECsis an easy tool to help you decide if animals need worming. The same amount (a teaspoon) of faeces should be collected from at least 10 animals in the groupand tested for the presence of worm eggs. This could be done on farm (if you have the kit), by your vet, or some agricultural merchants will offer theservice. A FEC will give an approximate measure of the severity of the worm burden present in the lambs. A discussion should be had with your vet/SQP/RAMA to discuss results along with your observations of the animals, as describedbelow.
*There are times whereFECs may not be appropriate, e.g. for the diagnosis of Nematodirus, where asignificant worm burden may be present and causing disease without seeing wormeggs in the faeces*.
2. Weight gain
The daily liveweight gain (DLWG) of lambs can be a useful tool to determine if lambs areaffected by a production-limiting disease such as PGE. The key here is to havethe ability to record and compare weight data quickly and easily e.g. with farm software. If your lambs are not growing as quickly as they should, you need to investigate. This tool in conjunction with FECs and observation of the flock’s cleanliness can help form a strategy for treatment.
3. Condition and cleanliness ofthe lambs
Last but certainly not least, you need to monitor your flock carefully for cleanliness of the back end, and condition of the animals. Spending some time assessing the flock visually for cleanliness is always going to be worthwhile, as well as putting your hand on the backs of the lambs to check condition. Again,recording condition will aid you in spotting trends and treating before you’re left with a more serious problem.
Choosing which lambs to worm
Once you have decided which group of lambs/ewes need treating, you then need to decide which animals to treat within the group.
Treating the whole group at once can lead to the acceleration of resistance developing. If all the animals in the group are treated with a wormer at the same time, then all the worms inside those lambs are being exposed to the drug. ONLY worms that are resistant to the wormer will survive the treatment and continue to produce eggs, which are subsequently released onto your pasture. This means that ALL the eggs being released onto your pasture are likely to have the genes that are resistant tothe wormer used.
We know that worms will affect lambs to varying degrees, so some animals that are clean and growing well may not needto be wormed. If you leave some animals in the group (e.g. the best 10%) untreated,you will be leaving a ‘normal’ population (resistant and susceptible) of wormsinside these animals to release a ‘normal’ population of eggs on your pasture. This reduces the selection pressure for resistance. This concept is called leavinga population ‘in refugia’.
Similarly, it is also good practice to send lambs back to their current pasture for 48 hours after worming before moving to ‘fresh’ pasture, to ensure they pick up a ‘normal’ population of worms, ratherthan just taking the resistant population to the new pasture.
Which wormer should I use?
You have decided you need to worm; you havea plan for leaving a worm population in refugia, now you need to decide whichwormer class to use.
There are three main wormer classes youcould use, with the addition of Moxidectin. Moxidectin is part of the Ivermectin, Group 3 wormers, but is classed separately as worms can be susceptible to Moxidectin even if they are resistant to Ivermectin wormers.
1. Group 1 BZ – White drench (Benzimidazoles) – (confusingly, these can also be green, cream, blue in colour) – for example Albex
2. Group 2 LV – Yellow drench(Levamisole) – for example Chanaverm
3. Group 3 ML* – Clear drench (Ivermectin, Doromectin)– for example Animec
a. Group 3 ML* – Clear drench (Moxidectin) – for example Moxodex , long-lasting residua activity for 5 weeks, with a dosing interval of 8 weeks and meat withdrawal of just 14 days
*Also available in injectable form
There are also two ‘newer’ classes of wormer. A quarantine treatment for all incoming animals, with wormer from the newer classes should be considered, in line with SCOPS recommendations and under veterinary or SQP/RAMA guidance. In addition, it has been suggested that one ofthese wormers be given as a one-off treatment for lambs, in the latter part ofthe grazing season. This protocol may slow the development of resistance forwormers in groups 1 to 3.
4. Group 4 AD – ‘Orange’ drench
5. Group 5 SI – ‘Purple’ drench - currently only licensed as a dual active with a 3-ML wormer inthe UK.
Knowing which wormer to use can beconfusing, as a large range of products is available, all with different tradenames. Selecting the right wormer is also very specific to your farm and sheep.
First, you must know which wormer classes are effective on your farm by testing the resistance profile of the worms present. Once you know what is effective, you can devise a strategy with your vet or SQP/RAMA as to which one to use and when. It is important to always use best practice when treating your flock for worms, and the SCOPS manual provides a useful guide for this.
In general, to reduce the chance of resistance, you need to rotate wormer classes within a season to ensure you are not repeatedly exposing worms to the same drug. The Chanelle anthelmintic range includes wormers for sheep across the three main wormer classes to help support responsible worming.
References:
1. WAARD_FINAL_PROJECT_REPORT_1_-_19-11-15.pdf(meatpromotion.wales)