Liver fluke is now present all over Scotland and is the most challenging parasite to control. Wetter summers and milder winters have extended the fluke season, with inappropriate treatment choices and drug resistance adding to the problems.

The liver fluke parasite ‘Fasciola hepatica’ lives in the bile ducts of cattle and sheep, but is also present in wildlife including deer and rabbits. The fluke parasite has an essential intermediate host, the mud snail ‘Galba truncatula’. This snail must be present on pasture to complete the life cycle. The snails are highly prolific and thrive in mild, wet conditions.

Sheep are most susceptible to fluke infections, a common cause of sudden death in the autumn due to the migration of large numbers of immature fluke in the liver. Sub-acute and chronic infections present with weight loss, anemia, and low blood protein/bottle jaw. Cattle, having different grazing habits and larger livers, tend to present with more chronic disease, with poor live weight gain or weight loss.

It takes more than 12 weeks for a liver fluke to become an adult and start laying eggs. Understanding the fluke life cycle is key to long-term control and choosing the best treatment options at different times of the year.

Autumn is the peak season for acute fluke infections caused by immature fluke, and the timing and level of this challenge can vary greatly, depending on the pasture conditions, rainfall, and the number of infected snails. Liver fluke diagnostic testing should be undertaken to find out the optimal time to dose.

Post-mortems of fallen stock are very valuable, allowing a definitive diagnosis of all stages of fluke infection. Abattoir returns are also very useful but should be taken with veterinary advice and further testing.

Blood antibody testing of first grazing season young stock is a useful tool – this is the earliest test that can be performed other than post-mortem to indicate new infections. Sampling 10 lambs or calves per group is recommended, with antibody levels rising three to four weeks after infection. Antibody levels can remain high even after successful treatment and in previously exposed older animals.

Coproantigen testing of dung samples will pick up mid to late stages of infection, especially useful in sheep. Results will detect infection from six to eight weeks before fluke eggs are present in the dung. Fluke egg counts in the dung are the definitive diagnosis of adult parasites in the liver, but this test is not useful for detecting early and late immature infections in the autumn. Test sensitivity may be low, especially in cattle, so must be interpreted with care.

Triclabendazole is the only drug that kills early immature infections and is still the cornerstone for autumn treatments. Timing of this treatment is key – dosing too early is a significant challenge and a waste of time and money. None of the flukicides have any persistence in activity, only killing what infection is already present.

Resistance is known to Triclabendazole in the UK but it is quite difficult to prove, often only anecdotal. Underdosing, heavy re-infection, and current liver damage can result in what looks like resistance. Please take veterinary advice if potential resistance is suspected.

No reported resistance to other fluke treatments has been recorded in the UK. However, it is recommended that different classes of drugs, at different times of the year, are used to treat the different stages of the life cycle. Do not rely on the same drug throughout the year.

Albendazole and Oxyclozanide should only be used in the spring/early summer, as they only kill adult fluke. It is an important time to dose, as adult fluke in the spring will be laying eggs, which infect the snails, contaminating the grazing for the following season. Do not use it as an autumn dose.

Beware of using combination products as they are often more expensive and can be ineffective if used at the wrong time.

Clorsulon and Closantel are often used in combination with Ivermectin as a fluke and worm dose. These should not be used as housing doses for cattle as they only treat adult and late immature fluke infections respectively. Cheaper, more effective, and responsible alternatives are available.

Dosing cattle for fluke is best done well after housing. Consider diagnostic testing before treatment and discuss with your animal health adviser or vet what product to use and when.

Nitroxynil and Clostantal are valuable drugs for treating later immature infections and are therefore a good choice for mid-winter dosing of sheep and cattle.

Be careful not to overdose on Clostantel as toxicity is common.

Rafoxanide has been imported from Europe and used to treat later immature fluke. However, it is closely related to Closantel. There is evidence of cross-resistance, therefore there is a serious risk that the use of Rafoxanide will hasten the development of resistance to Clostantel.

Please consult with a veterinary adviser when deciding what products to use and when. This may vary from year to year depending on the fluke risk. Post-mortem examinations of fallen stock are really valuable and consider blood testing and dung testing before you treat.