As I travel up and down the country discussing animal health, there is one topic that draws confusion. When the discussion turns to parasites, farmers can get frustrated and are always asking what the best dose for worms is. To add further to this frustration, I have to reinforce that parasites are never that simple.
Human nature means we always want the easiest and often the fastest solution to any problem. For many years with parasites we have had that easy solution in reasonably priced worming products. The development of resistance (where the parasites adapt to the wormers, making them resistant to the mechanisms they use to kill them) has changed the game.
With no new worming products or active ingredients in the pipeline short cuts become less of an option. This year has seen a longer grazing season and also the ideal weather conditions for worms, particularly lungworm.
It always strikes me that we have three active ingredients for wormers in cattle and four for sheep.
White: benzimidazoles kill larvae and adults. They have no persistency.Yellow: levamisoles only kill adult worms. They have no persistency.Clear: MLs or ivermectins. They kill all stages and have varying levels of persistency depending on the product. Orange: monepantel – sheep only.There are close to 130 worming products on the market with different brand names. This means that when we pick a product we too often do this based on brand name and not on the active ingredient.
Worm doses have got cheaper, meaning the decision to use them is based less on cost. These are vital products with no new products being brought to the market. We also have the emerging reality in cattle of anthelmintic or wormer resistance, where the worms are becoming resistant to the wormers. This has been a reality in our flocks for the last decade and now evidence is saying it is beginning in our cattle.
So a good control plan should be developed with an eye on many pieces of the jigsaw.
The weather
Over the last 10 years, we also have seen variable weather patterns which have seen wetter milder springs and summers in general. Last summer, we experienced a drought which had an impact on worms on pasture. We saw very few worm issues during the drought of 2018.
The weather is important because most of the parasite’s life is spent outside animals. They are developing from egg to larvae which is often ingested by the final host. As fluke has an intermediate host – the mud snail – the weather plays a big role on the risk. Most worm larvae need rainwater to disperse them by splashing from the dung paths on to the grass. This is why we look at weather as a risk.
Parasites generally don’t like very low temperatures below -10°C or prolonged dry heat. This year so far has been showing the exact conditions required by parasites.
Clinical signs
We must also look at clinical signs. This is so important with lungworm as it can be very unpredictable. We must be reactive towards coughing in particular but also signs such as scour or wet faecal staining.
Weights
Most farming systems from lambs to calves are in the business of weight gain with daily liveweight gain being a very good metric of performance.
When we are achieving good daily liveweight gains, it means the system is working.
Weights at grass will be useful when considering parasites and also when we decide about dosing animals for worms, with some farms now choosing only to dose underweight animals or those that are not thriving. Animals that are thriving may not need a dose. This means leaving 10% of a group that are above weight targets not dosed.
Grazing management
Grazing strategies must be taken into account as parasites are an outdoor problem. You need to be aware of any conditions that help parasite numbers increase. Most larvae are found low down in grass and intensive grazing systems increase the parasite risk.
If larvae survive year to year like this winter, then young stock going on to the same pastures each spring are at risk.
Faecal egg counts
Faecal egg counts (FECs) can also play a part in assessing the risk for your farm. I find the best value are pooled samples from stock on a regular basis. This is done by estimating eggs in one gram of faeces.
Table 1 broadly outlines how to read this risk.
For example, 50 calves or lambs in the first grazing season start doing FECs monthly four to six weeks after turnout. This may be extended if other risks are lower.
Suckler calves are usually lower risk and this can often be six to eight weeks after turnout.
Use FECs every two months in second grazers and use them at key times for your cows, such as at housing, to assess both worms and fluke.
FECs can also be used on animals that are not performing to help with diagnosis and treatment decisions.
Remember, younger animals are more at risk because they have not developed an immunity to gut worms.
Animals will never develop immunity to fluke and this means the parasite will require management in all age groups on farm where liver fluke is a risk.
By looking at all the risks, we can draw up proactive parasite control plans that may take more work but will help tackle the problem of anthelmintic resistance.
As I travel up and down the country discussing animal health, there is one topic that draws confusion. When the discussion turns to parasites, farmers can get frustrated and are always asking what the best dose for worms is. To add further to this frustration, I have to reinforce that parasites are never that simple.
Human nature means we always want the easiest and often the fastest solution to any problem. For many years with parasites we have had that easy solution in reasonably priced worming products. The development of resistance (where the parasites adapt to the wormers, making them resistant to the mechanisms they use to kill them) has changed the game.
With no new worming products or active ingredients in the pipeline short cuts become less of an option. This year has seen a longer grazing season and also the ideal weather conditions for worms, particularly lungworm.
It always strikes me that we have three active ingredients for wormers in cattle and four for sheep.
White: benzimidazoles kill larvae and adults. They have no persistency.Yellow: levamisoles only kill adult worms. They have no persistency.Clear: MLs or ivermectins. They kill all stages and have varying levels of persistency depending on the product. Orange: monepantel – sheep only.There are close to 130 worming products on the market with different brand names. This means that when we pick a product we too often do this based on brand name and not on the active ingredient.
Worm doses have got cheaper, meaning the decision to use them is based less on cost. These are vital products with no new products being brought to the market. We also have the emerging reality in cattle of anthelmintic or wormer resistance, where the worms are becoming resistant to the wormers. This has been a reality in our flocks for the last decade and now evidence is saying it is beginning in our cattle.
So a good control plan should be developed with an eye on many pieces of the jigsaw.
The weather
Over the last 10 years, we also have seen variable weather patterns which have seen wetter milder springs and summers in general. Last summer, we experienced a drought which had an impact on worms on pasture. We saw very few worm issues during the drought of 2018.
The weather is important because most of the parasite’s life is spent outside animals. They are developing from egg to larvae which is often ingested by the final host. As fluke has an intermediate host – the mud snail – the weather plays a big role on the risk. Most worm larvae need rainwater to disperse them by splashing from the dung paths on to the grass. This is why we look at weather as a risk.
Parasites generally don’t like very low temperatures below -10°C or prolonged dry heat. This year so far has been showing the exact conditions required by parasites.
Clinical signs
We must also look at clinical signs. This is so important with lungworm as it can be very unpredictable. We must be reactive towards coughing in particular but also signs such as scour or wet faecal staining.
Weights
Most farming systems from lambs to calves are in the business of weight gain with daily liveweight gain being a very good metric of performance.
When we are achieving good daily liveweight gains, it means the system is working.
Weights at grass will be useful when considering parasites and also when we decide about dosing animals for worms, with some farms now choosing only to dose underweight animals or those that are not thriving. Animals that are thriving may not need a dose. This means leaving 10% of a group that are above weight targets not dosed.
Grazing management
Grazing strategies must be taken into account as parasites are an outdoor problem. You need to be aware of any conditions that help parasite numbers increase. Most larvae are found low down in grass and intensive grazing systems increase the parasite risk.
If larvae survive year to year like this winter, then young stock going on to the same pastures each spring are at risk.
Faecal egg counts
Faecal egg counts (FECs) can also play a part in assessing the risk for your farm. I find the best value are pooled samples from stock on a regular basis. This is done by estimating eggs in one gram of faeces.
Table 1 broadly outlines how to read this risk.
For example, 50 calves or lambs in the first grazing season start doing FECs monthly four to six weeks after turnout. This may be extended if other risks are lower.
Suckler calves are usually lower risk and this can often be six to eight weeks after turnout.
Use FECs every two months in second grazers and use them at key times for your cows, such as at housing, to assess both worms and fluke.
FECs can also be used on animals that are not performing to help with diagnosis and treatment decisions.
Remember, younger animals are more at risk because they have not developed an immunity to gut worms.
Animals will never develop immunity to fluke and this means the parasite will require management in all age groups on farm where liver fluke is a risk.
By looking at all the risks, we can draw up proactive parasite control plans that may take more work but will help tackle the problem of anthelmintic resistance.
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