The rate at which anthelmintic resistance is developing to commonly used wormers is threatening future sheep production systems. Teagasc sheep specialist Ciaran Lynch says that nationally, anthelmintic resistance, or the ability of parasites to survive a dose that should kill them, is increasing at a worrying rate.
Ciaran Lynch, president of the Irish Grassland Association. \ Barry Cronin
Ciaran says: “part of the problem is that you cannot readily see anthelmintic resistance physically developing in animals and as such, many farmers think it will not affect them and continue to implement the same worm control programmes until it is too late.
“We have a worrying number of farmers who now have resistance to the three most common products – group one benzimidazoles (BZ) or white wormers, group two levamisoles (LV) or yellow wormers and group three macrocyclic lactones (ML) or clear wormers. These farmers are greatly curtailed in the options that they have and we are urging more farmers to become aware of the threats before it is too late.”
Teagasc has this week launched a sustainable worm control initiative to help slow the rate of anthilmintic resistance. The initiative has four targets, which, if applicable, should be followed.
1 Don’t treat adult ewes without reason
The idea of not administering worm treatments to mature ewes was raised at this year’s Teagasc lowland and hill sheep conferences and generated a high level of discussion among farmers who routinely treat ewes pre-lambing.
Healthy adult ewes have good immunity to stomach worms and do not need worm treatment. The only animals that should be considered are lactating yearly hoggets and thin/compromised mature ewes. If there is a high number of the latter category, then an investigation should take place to identify the underlying causes.
As well as ewes not needing treatment, untreated ewes also help to maintain a population of susceptible worms within a farm. A new recommendation suggests avoiding using injectable group three-ML products for external parasite control.
The reasoning for this is that these products also target worms and therefore typically represent worm treatment that is not required, which in turn will increase the rate of resistance developing.
2 Avoid group one-BZ later in
season
In recent years, group one-BL products were advised to be used for nematodirus in lambs. This advice remains constant, with no detected incidence of anthelmintic resistance to nematodirus.
Given the low efficacy of group one-BZ products against other stomach worms, the advice from Teagasc is that these products are not a suitable choice for treating lambs for worms later in the season.
3 Prevent buying in resistance
There is a high risk of introducing anthelmintic resistance to a flock through purchasing sheep and not following a robust quarantine protocol. Teagasc recommend a two-treatment approach using one of two options. The first is treating lambs with a group four-AD (Amino-acetonitrile derivites) product, which currently is Zolvix, along with either a group two-LV or group three-ML product.
The second option includes treatment with a group five-SI (spirindoles) product, along with a group two-LV. The second option is not available to farmers in Ireland as Startect, the only five-SI product, is currently not on the market. It is also worth noting that Zolvix is a prescription-only medicine and as such, has to be ordered through your vet. It is worth ordering the product well in advance, as it is not often readily available.
Sheep should also remain housed on arrival to the farm to prevent resistant worms from being shed onto pasture and should be housed for 48 hours after treatment. Following this, purchased sheep should be grazed in ‘dirty’ pasture that has been grazed by sheep and contains a population of susceptible worms.
4 Faecal egg count/drench test
The use of faecal egg tests is highly recommended to determine the need for dosing from weaning in June to September.
There are two protocols advised for collecting at least 10 individual fresh samples. The first of these is gathering sheep in a corner of a field for a few minutes and collecting the required fresh samples. The second option is selecting a group of 15 lambs at random and holding them in a clean pen for a period to collect samples.
Ciaran says: “The advice to collect samples in a corner of a field is different from the usual advice of collecting samples in a pen, but we have to be realistic and work with the circumstances farmers are faced with.
When many farmers go to the hassle of putting sheep in a pen, they will automatically dose them, as it can be a significant task that they do not want to repeat. This recommendation will hopefully increase the number of farmers submitting and using faecal egg counts to determine the need to dose for worms.”
Drench test
A drench test can be successfully used to determine if anthelmintic resistance is a problem on the farm. It is a six step process as follows:
Contact an approved lab or relevant body for a sampling kit.Select a group of 15 lambs at random and hold in a clean pen. Mark or record tag numbers to allow for easy identification when repeat sampling. Collect 10 fresh dung samples and place in the containers provided.Dose lambs with the chosen product while following best practice to ensure the dosing procedure is not at fault for the treatment potentially not working. This includes calibrating dosing equipment, correctly dosing to the heaviest in the groups and following the manufacturer’s instructions. Post the samples as soon as possible, preferably on the day of sampling. If there is a delay, place the samples in a refrigerator or cooler box. Do not freeze or leave in direct sunlight. A repeat post treatment sample is required to check for resistance. This should take place seven days later for group two-LV products and 14 days later for group one-BZ or group three-ML products. Calculate the percentage reduction as follows;(Egg count Test1 - egg count Test2) x 100.
Egg count test
A greater than 95% reduction shows that the product is working effectively. A reduction of less than 95% shows the product is not working effectively. The initial egg count would need to be in excess of 200 epg (ie burden present) to draw conclusions regarding product efficacy.
If count is lower, repeat at the next dosing interval.
The rate at which anthelmintic resistance is developing to commonly used wormers is threatening future sheep production systems. Teagasc sheep specialist Ciaran Lynch says that nationally, anthelmintic resistance, or the ability of parasites to survive a dose that should kill them, is increasing at a worrying rate.
Ciaran Lynch, president of the Irish Grassland Association. \ Barry Cronin
Ciaran says: “part of the problem is that you cannot readily see anthelmintic resistance physically developing in animals and as such, many farmers think it will not affect them and continue to implement the same worm control programmes until it is too late.
“We have a worrying number of farmers who now have resistance to the three most common products – group one benzimidazoles (BZ) or white wormers, group two levamisoles (LV) or yellow wormers and group three macrocyclic lactones (ML) or clear wormers. These farmers are greatly curtailed in the options that they have and we are urging more farmers to become aware of the threats before it is too late.”
Teagasc has this week launched a sustainable worm control initiative to help slow the rate of anthilmintic resistance. The initiative has four targets, which, if applicable, should be followed.
1 Don’t treat adult ewes without reason
The idea of not administering worm treatments to mature ewes was raised at this year’s Teagasc lowland and hill sheep conferences and generated a high level of discussion among farmers who routinely treat ewes pre-lambing.
Healthy adult ewes have good immunity to stomach worms and do not need worm treatment. The only animals that should be considered are lactating yearly hoggets and thin/compromised mature ewes. If there is a high number of the latter category, then an investigation should take place to identify the underlying causes.
As well as ewes not needing treatment, untreated ewes also help to maintain a population of susceptible worms within a farm. A new recommendation suggests avoiding using injectable group three-ML products for external parasite control.
The reasoning for this is that these products also target worms and therefore typically represent worm treatment that is not required, which in turn will increase the rate of resistance developing.
2 Avoid group one-BZ later in
season
In recent years, group one-BL products were advised to be used for nematodirus in lambs. This advice remains constant, with no detected incidence of anthelmintic resistance to nematodirus.
Given the low efficacy of group one-BZ products against other stomach worms, the advice from Teagasc is that these products are not a suitable choice for treating lambs for worms later in the season.
3 Prevent buying in resistance
There is a high risk of introducing anthelmintic resistance to a flock through purchasing sheep and not following a robust quarantine protocol. Teagasc recommend a two-treatment approach using one of two options. The first is treating lambs with a group four-AD (Amino-acetonitrile derivites) product, which currently is Zolvix, along with either a group two-LV or group three-ML product.
The second option includes treatment with a group five-SI (spirindoles) product, along with a group two-LV. The second option is not available to farmers in Ireland as Startect, the only five-SI product, is currently not on the market. It is also worth noting that Zolvix is a prescription-only medicine and as such, has to be ordered through your vet. It is worth ordering the product well in advance, as it is not often readily available.
Sheep should also remain housed on arrival to the farm to prevent resistant worms from being shed onto pasture and should be housed for 48 hours after treatment. Following this, purchased sheep should be grazed in ‘dirty’ pasture that has been grazed by sheep and contains a population of susceptible worms.
4 Faecal egg count/drench test
The use of faecal egg tests is highly recommended to determine the need for dosing from weaning in June to September.
There are two protocols advised for collecting at least 10 individual fresh samples. The first of these is gathering sheep in a corner of a field for a few minutes and collecting the required fresh samples. The second option is selecting a group of 15 lambs at random and holding them in a clean pen for a period to collect samples.
Ciaran says: “The advice to collect samples in a corner of a field is different from the usual advice of collecting samples in a pen, but we have to be realistic and work with the circumstances farmers are faced with.
When many farmers go to the hassle of putting sheep in a pen, they will automatically dose them, as it can be a significant task that they do not want to repeat. This recommendation will hopefully increase the number of farmers submitting and using faecal egg counts to determine the need to dose for worms.”
Drench test
A drench test can be successfully used to determine if anthelmintic resistance is a problem on the farm. It is a six step process as follows:
Contact an approved lab or relevant body for a sampling kit.Select a group of 15 lambs at random and hold in a clean pen. Mark or record tag numbers to allow for easy identification when repeat sampling. Collect 10 fresh dung samples and place in the containers provided.Dose lambs with the chosen product while following best practice to ensure the dosing procedure is not at fault for the treatment potentially not working. This includes calibrating dosing equipment, correctly dosing to the heaviest in the groups and following the manufacturer’s instructions. Post the samples as soon as possible, preferably on the day of sampling. If there is a delay, place the samples in a refrigerator or cooler box. Do not freeze or leave in direct sunlight. A repeat post treatment sample is required to check for resistance. This should take place seven days later for group two-LV products and 14 days later for group one-BZ or group three-ML products. Calculate the percentage reduction as follows;(Egg count Test1 - egg count Test2) x 100.
Egg count test
A greater than 95% reduction shows that the product is working effectively. A reduction of less than 95% shows the product is not working effectively. The initial egg count would need to be in excess of 200 epg (ie burden present) to draw conclusions regarding product efficacy.
If count is lower, repeat at the next dosing interval.
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