How can farmers reduce the incidence of liver fluke in sheep?
Liver fluke (Fasciola hepatica) is known to cause severe clinical disease and death in sheep flocks throughout Ireland and can be found mainly in wet pastures.
In sheep, liver fluke can be classed as either acute or chronic.
Acute infection is highly pathogenic. This type is often seen in younger animals and is caused by the activity of immature fluke in the liver – causing bleeding and severe liver damage.
Chronic infection is a result of a prolonged intake of cysts and leads to the degenerative loss of body condition; however, death is rare in well-nourished animals.
There are four ways in farmers can control the incidence of liver fluke.
- Pasture protection;
- Pasture management;
- Grazing management;
- Strategic treatments.
Pasture protection involves preventing liver fluke from reaching pastures when the mud snail is active.
Treating animals in early spring and summer reduces the adult fluke burden, in turn, reducing the number of eggs reaching pastures that the animals could potentially ingest.
Furthermore, removing the eggs from pastures during this period when mud snails are most active will reduce the numbers of infected snails which will be beneficial to flock health over the autumn and winter period.
Improving pasture management practices will reduce the prevalence of liver fluke, as the contact between the host and affected animal is reduced.
The main elements to consider are:
- Fixing leaky troughs;
- Avoid poached ground;
- Spraying and topping rushes; and
- Maintaining effective drainage.
Good grazing management practices will also reduce the incidence of liver fluke.
Reducing contact with high-risk areas such as wet and boggy ground will significantly reduce the risk of liver fluke infection.
This should be practiced from late autumn to early spring as this is the high-risk period of infection.
The usual products that farmers have treated liver fluke with in the past – during the autumn and winter period – are no longer effective. This is because liver fluke has become more common throughout the year.
Farmers are in disbelief when sheep die at this time of the year because they have treated the animal for this parasite.
This is down to the fact that these products are only killing the mature fluke and not the immature type which is the cause of these deaths.
Adult and immature liver fluke should be targeted in late winter and spring as the number of infectious larvae on pasture during this period will be minimal.