Liver fluke in dairy cattle
- What is liver fluke?
- What are the clinical signs?
- Is my farm at risk?
- How do I diagnose liver fluke?
- How do I treat liver fluke?
- Can I prevent liver fluke?
Liver fluke, or Fasciola hepatica, is a parasite which can infect cattle and sheep. It can cause severe liver damage leading to significant losses in dairy production.1 It is estimated that 50-80% of UK dairy herds have liver fluke exposure, especially in wetter areas that are optimal for the liver fluke life cycle.
Cull cows which have previously had liver fluke may have their liver condemned in the abattoir due to scarring. AHDB data showed that around 7% of cattle livers are condemned for liver fluke, and that condemned livers in cattle and sheep cost around £3 million annually.2
What is liver fluke?
The liver fluke parasite Fasciola hepatica is an unusual parasite as it requires the presence of mud snails in the environment to complete its life cycle. This means that the highest risk periods for livestock picking up liver fluke are usually the wetter seasons when mud snails are prevalent – so clinical signs are usually seen in late autumn and winter.
Infected cows and sheep excrete liver fluke eggs onto the pasture in their faeces. These hatch out after a period of time (depending on weather and temperature conditions) into a larval stage. This larval stage must find a suitable mud snail host within a few hours to survive. Once inside the mud snail the larval stage replicates hundreds or thousands of times into the next stage, cercaria, which break out of the snail and swim to nearby vegetation. Here they develop into the cyst stage (metacercaria) which remain on the vegetation until they are eaten by grazing livestock.
Once inside the host, the cysts hatch in the gut. They penetrate the gut wall and move through the abdomen to the liver. They burrow through the liver, in some cases causing significant liver damage, and enter the biliary system, eventually maturing in the bile duct and shedding eggs into the gut to start the cycle again. This host part of the life cycle takes up to 12 weeks before fluke starts to shed eggs.
What are the clinical signs?
In heifers, liver fluke is associated with reduced growth rates. Both heifers and cows with heavy liver fluke burdens can show clinical signs of disease: weight loss, scour and/or fluid swelling under the jaw (‘bottle jaw’). Affected cows also show reduced milk production and poorer fertility. If left untreated it can lead to welfare issues due to significant weight loss.
However, apparently healthy cows in herds with high levels of liver fluke also have reduced productivity. Bulk tank milk samples which are highly positive for liver fluke antibody are associated with around 1.5L/cow/day decrease in milk production3 and poorer fertility with an average 4-day increase in Calving Interval4.
Is my farm at risk?
Mud snails prefer areas that tend to become waterlogged and boggy, so cattle or sheep grazing this land are at risk. Silage made from these areas is considered low risk as long as it has been well made.
Examples of areas that are high risk for mud snails include: stream banks, areas around ponds, ruts in tracks, natural undulations in fields, areas of poaching, cleared ditches, or around leaking water troughs.
How do I diagnose liver fluke?
Liver fluke infection can be diagnosed in a number of ways. Post-mortem examination of the liver of suspect cases can be extremely useful in detecting either active fluke (the presence of fluke parasites within the liver) or historic fluke (the typical scarring seen after previous fluke infections). A combination of post-mortem exam results, along with abattoir feedback from any cull cows, can help assess the fluke status of a farm.
Live animals can be tested for fluke either if they are showing clinical signs, or if screening a group of apparently healthy animals to determine whether they have been exposed to fluke recently. There are several options for testing for fluke in live animals:
• Fluke eggs in faeces - Testing for fluke eggs in the faeces of cattle is quick and relatively cheap, but this test is only useful in the later stages of infection as it takes up to 12 weeks after entering the host for the fluke to mature and start producing eggs. This means the test is most useful in detecting fluke in late winter onwards, or in detecting chronic fluke in herds which do not have any routine fluke treatment in place.
• Faecal copro-antigen test - This detects a protein produced by immature fluke after around 6 weeks in the host. This means this test can detect fluke weeks earlier than the fluke egg test. It is more expensive than testing for fluke eggs but is useful when testing animals in early autumn/winter.
• Blood antibody testing – Once animals are exposed to liver fluke they start to produce antibodies to fluke, which build up in the bloodstream and the milk. We can measure antibody levels in blood – positive samples indicate the animal has been exposed to fluke, although antibodies remain positive for some time after treatment so it does not always mean there is a current infection.
• Milk antibody testing – Bulk milk samples can be tested for the presence of fluke antibodies. The level of antibodies in the milk can be used to determine roughly what proportion of the herd has likely been exposed and how significant the effects are likely to be. This is a cheap, rapid test which can be a good screening tool for apparently healthy groups of milking cows.
How do I treat liver fluke?
Flukicides (products which treat liver fluke) must be used with care in dairy herds as there are many products which are not safe for humans. Use of these products in milking cows (or in dry cows or heifers near to calving) would contaminate the bulk tank and lead to the milk processor refusing to accept the milk from that herd. For this reason, it is important to use only products safe for the particular class of stock being treated:
Be aware that these guidelines are for single ingredient products – combination fluke and worm products may have more restrictions on their use and the datasheet should be checked before using in pregnant/milking cattle.
More details on treatment timing for non-pregnant youngstock relating to housing etc. can be found in ‘Management of parasites in beef and dairy cattle around housing’.
In the UK there have been many reports of flukicide resistance in both cattle and sheep farms, especially to triclabendazole products used to treat immature fluke. It is possible to minimise the risk of flukicide resistance on farms by:
• Screening groups of animals before treating and saving flukicides for when they are needed
• Using the most appropriate type of flukicide for the class of animal and the time of year
• Treat animals at the optimal time for the best results (depending on pasture type, stock type and the weather conditions that year)
• Weigh stock so they are dosed for an accurate weight
• Ensure guns for Pour-on or Oral treatments are calibrated before use and regularly checked during treatment of large groups
• Work with the farm vet to test animals for resistance (using faecal samples pre- and post-treatment)
• Work with the farm vet to ensure that purchased animals which may have been exposed to fluke are suitably treated while in quarantine.
Can I prevent liver fluke?
If fluke is not already present on the farm then it is vital to have a quarantine/treatment plan with the farm vet to prevent bought-in sheep or cattle from bringing fluke in.
In farms where fluke is already present, prevention is mainly down to pasture management and monitoring groups of stock to identify when treatment is necessary. This can be through testing as described above or using abattoir feedback.
Firstly, mapping the farmland will help identify high risk areas – these may be an entire pasture or may be an area of pasture which is optimal for mud snail survival. Some high-risk areas may be modified – for example, maintenance of water troughs to prevent leaks; improving tracks and gateways to reduce poaching of high-use areas; or drainage of boggy areas. If these are not possible then fencing these areas off may be practical – otherwise, avoid grazing high-risk pastures in autumn.
Finally, be aware that the relevant species of fluke (Fasciola hepatica) can infect both sheep and cattle. This means that unlike in control of gut worms where co-grazing can reduce pasture burdens, co-grazing cattle and sheep can increase fluke larval burden on the pasture and so increase the risk of clinical fluke in both species.
References:
1. Howell AK, Tongue SC, Currie C, Evans J, Williams DJL, McNeilly TN. Co-infection with Fasciola hepatica may increase the risk of Escherichia coli O157 shedding in British cattle destined for the food chain. Prev Vet Med. 2018 Feb 1;150:70-76. doi: 10.1016/j.prevetmed.2017.12.007. Epub 2017 Dec 7. PMID: 29406086; PMCID: PMC5812777.
2. https://ahdb.org.uk/knowledge-library/liver-fluke-control-in-grazing-livestock 2021 figures
3. Mezo M, González-Warleta M, Castro-Hermida JA, Muiño L, Ubeira FM. Association between anti-F. hepatica antibody levels in milk and production losses in dairy cows. Vet Parasitol. 2011 Aug 25;180(3-4):237-42.
4. Charlier J, Duchateau L, Claerebout E, Williams D, Vercruysse J. Associations between anti-Fasciola hepatica antibody levels in bulk-tank milk samples and production parameters in dairy herds. Prev Vet Med. 2007 Jan 16;78(1):57-66.
Liver fluke in dairy cattle
- What is liver fluke?
- What are the clinical signs?
- Is my farm at risk?
- How do I diagnose liver fluke?
- How do I treat liver fluke?
- Can I prevent liver fluke?
Liver fluke, or Fasciola hepatica, is a parasite which can infect cattle and sheep. It can cause severe liver damage leading to significant losses in dairy production.1 It is estimated that 50-80% of UK dairy herds have liver fluke exposure, especially in wetter areas that are optimal for the liver fluke life cycle.
Cull cows which have previously had liver fluke may have their liver condemned in the abattoir due to scarring. AHDB data showed that around 7% of cattle livers are condemned for liver fluke, and that condemned livers in cattle and sheep cost around £3 million annually.2
What is liver fluke?
The liver fluke parasite Fasciola hepatica is an unusual parasite as it requires the presence of mud snails in the environment to complete its life cycle. This means that the highest risk periods for livestock picking up liver fluke are usually the wetter seasons when mud snails are prevalent – so clinical signs are usually seen in late autumn and winter.
Infected cows and sheep excrete liver fluke eggs onto the pasture in their faeces. These hatch out after a period of time (depending on weather and temperature conditions) into a larval stage. This larval stage must find a suitable mud snail host within a few hours to survive. Once inside the mud snail the larval stage replicates hundreds or thousands of times into the next stage, cercaria, which break out of the snail and swim to nearby vegetation. Here they develop into the cyst stage (metacercaria) which remain on the vegetation until they are eaten by grazing livestock.
Once inside the host, the cysts hatch in the gut. They penetrate the gut wall and move through the abdomen to the liver. They burrow through the liver, in some cases causing significant liver damage, and enter the biliary system, eventually maturing in the bile duct and shedding eggs into the gut to start the cycle again. This host part of the life cycle takes up to 12 weeks before fluke starts to shed eggs.
What are the clinical signs?
In heifers, liver fluke is associated with reduced growth rates. Both heifers and cows with heavy liver fluke burdens can show clinical signs of disease: weight loss, scour and/or fluid swelling under the jaw (‘bottle jaw’). Affected cows also show reduced milk production and poorer fertility. If left untreated it can lead to welfare issues due to significant weight loss.
However, apparently healthy cows in herds with high levels of liver fluke also have reduced productivity. Bulk tank milk samples which are highly positive for liver fluke antibody are associated with around 1.5L/cow/day decrease in milk production3 and poorer fertility with an average 4-day increase in Calving Interval4.
Is my farm at risk?
Mud snails prefer areas that tend to become waterlogged and boggy, so cattle or sheep grazing this land are at risk. Silage made from these areas is considered low risk as long as it has been well made.
Examples of areas that are high risk for mud snails include: stream banks, areas around ponds, ruts in tracks, natural undulations in fields, areas of poaching, cleared ditches, or around leaking water troughs.
How do I diagnose liver fluke?
Liver fluke infection can be diagnosed in a number of ways. Post-mortem examination of the liver of suspect cases can be extremely useful in detecting either active fluke (the presence of fluke parasites within the liver) or historic fluke (the typical scarring seen after previous fluke infections). A combination of post-mortem exam results, along with abattoir feedback from any cull cows, can help assess the fluke status of a farm.
Live animals can be tested for fluke either if they are showing clinical signs, or if screening a group of apparently healthy animals to determine whether they have been exposed to fluke recently. There are several options for testing for fluke in live animals:
• Fluke eggs in faeces - Testing for fluke eggs in the faeces of cattle is quick and relatively cheap, but this test is only useful in the later stages of infection as it takes up to 12 weeks after entering the host for the fluke to mature and start producing eggs. This means the test is most useful in detecting fluke in late winter onwards, or in detecting chronic fluke in herds which do not have any routine fluke treatment in place.
• Faecal copro-antigen test - This detects a protein produced by immature fluke after around 6 weeks in the host. This means this test can detect fluke weeks earlier than the fluke egg test. It is more expensive than testing for fluke eggs but is useful when testing animals in early autumn/winter.
• Blood antibody testing – Once animals are exposed to liver fluke they start to produce antibodies to fluke, which build up in the bloodstream and the milk. We can measure antibody levels in blood – positive samples indicate the animal has been exposed to fluke, although antibodies remain positive for some time after treatment so it does not always mean there is a current infection.
• Milk antibody testing – Bulk milk samples can be tested for the presence of fluke antibodies. The level of antibodies in the milk can be used to determine roughly what proportion of the herd has likely been exposed and how significant the effects are likely to be. This is a cheap, rapid test which can be a good screening tool for apparently healthy groups of milking cows.
How do I treat liver fluke?
Flukicides (products which treat liver fluke) must be used with care in dairy herds as there are many products which are not safe for humans. Use of these products in milking cows (or in dry cows or heifers near to calving) would contaminate the bulk tank and lead to the milk processor refusing to accept the milk from that herd. For this reason, it is important to use only products safe for the particular class of stock being treated:
Be aware that these guidelines are for single ingredient products – combination fluke and worm products may have more restrictions on their use and the datasheet should be checked before using in pregnant/milking cattle.
More details on treatment timing for non-pregnant youngstock relating to housing etc. can be found in ‘Management of parasites in beef and dairy cattle around housing’.
In the UK there have been many reports of flukicide resistance in both cattle and sheep farms, especially to triclabendazole products used to treat immature fluke. It is possible to minimise the risk of flukicide resistance on farms by:
• Screening groups of animals before treating and saving flukicides for when they are needed
• Using the most appropriate type of flukicide for the class of animal and the time of year
• Treat animals at the optimal time for the best results (depending on pasture type, stock type and the weather conditions that year)
• Weigh stock so they are dosed for an accurate weight
• Ensure guns for Pour-on or Oral treatments are calibrated before use and regularly checked during treatment of large groups
• Work with the farm vet to test animals for resistance (using faecal samples pre- and post-treatment)
• Work with the farm vet to ensure that purchased animals which may have been exposed to fluke are suitably treated while in quarantine.
Can I prevent liver fluke?
If fluke is not already present on the farm then it is vital to have a quarantine/treatment plan with the farm vet to prevent bought-in sheep or cattle from bringing fluke in.
In farms where fluke is already present, prevention is mainly down to pasture management and monitoring groups of stock to identify when treatment is necessary. This can be through testing as described above or using abattoir feedback.
Firstly, mapping the farmland will help identify high risk areas – these may be an entire pasture or may be an area of pasture which is optimal for mud snail survival. Some high-risk areas may be modified – for example, maintenance of water troughs to prevent leaks; improving tracks and gateways to reduce poaching of high-use areas; or drainage of boggy areas. If these are not possible then fencing these areas off may be practical – otherwise, avoid grazing high-risk pastures in autumn.
Finally, be aware that the relevant species of fluke (Fasciola hepatica) can infect both sheep and cattle. This means that unlike in control of gut worms where co-grazing can reduce pasture burdens, co-grazing cattle and sheep can increase fluke larval burden on the pasture and so increase the risk of clinical fluke in both species.
References:
1. Howell AK, Tongue SC, Currie C, Evans J, Williams DJL, McNeilly TN. Co-infection with Fasciola hepatica may increase the risk of Escherichia coli O157 shedding in British cattle destined for the food chain. Prev Vet Med. 2018 Feb 1;150:70-76. doi: 10.1016/j.prevetmed.2017.12.007. Epub 2017 Dec 7. PMID: 29406086; PMCID: PMC5812777.
2. https://ahdb.org.uk/knowledge-library/liver-fluke-control-in-grazing-livestock 2021 figures
3. Mezo M, González-Warleta M, Castro-Hermida JA, Muiño L, Ubeira FM. Association between anti-F. hepatica antibody levels in milk and production losses in dairy cows. Vet Parasitol. 2011 Aug 25;180(3-4):237-42.
4. Charlier J, Duchateau L, Claerebout E, Williams D, Vercruysse J. Associations between anti-Fasciola hepatica antibody levels in bulk-tank milk samples and production parameters in dairy herds. Prev Vet Med. 2007 Jan 16;78(1):57-66.