Now’s the time to monitor the impact of liver fluke in your herd
Liver fluke (fasciolosis) is a parasitic disease that affects grazing animals, particularly those grazed on wet and muddy pastures near rivers or ponds. The life cycle requires mud snails as an intermediate host, and warm summers with heavy rainfall, such as this year, provide the ideal environment for them to develop and thrive. The infective stages of the fluke life cycle are at their peak from late August to October, so now is the highest risk period for infection. Once ingested by cattle (or sheep) the immature fluke develop whilst migrating through the liver, causing liver damage, before reaching the bile ducts to fully mature and begin producing eggs.
Unlike gut worms, cattle do not develop immunity to liver fluke, therefore any dairy animal grazing pastures with mud snail habitats from August onwards is potentially at risk of fluke infection.
How does fluke affect dairy cows?
•Reduced milk yield
•Reduced butterfat and protein
•Reduced feed conversion efficiency and dry matter intake
What other clinical signs are seen?
Chronic infection usually presents over the Winter period as:
•Weight loss/poor condition
•Occasionally fluid swelling under jaw +/- anaemia
Infection can also predispose cattle to co-infection with Salmonella or Black disease (clostridial disease of the liver). Once fluke are in the liver they can survive there for months, and in many cases years, unless an effective treatment is given.
How do I diagnose fluke on my farm?
•Abattoir reports are often the first indication of an issue on farm. Adult fluke and the associated liver damage are easily picked up at postmortem, so monitor barren cow reports.
Bulk tank antibody testing can be used routinely throughout the year to indicate the level of infection within the herd. This can also be carried out on individual milk samples.
•Blood sample antibody testing – antibodies are produced as early as 2 weeks post-infection but can persist for months afterwards, so a positive result may not necessarily indicate current infection.
•Faecal egg counts – can be performed on both individual and pooled samples, but will only detect infection if adult fluke are present and shedding eggs, which only occurs from 12 weeks after infection onwards. Egg counts only detect current infection and are most reliable in late Winter/early Spring.
•Faecal copra-antigen testing – can detect infection from as early as 4-6 weeks and is useful for testing of individual samples. This will also only detect current infection.
How do I treat fluke?
Cows in milk:
The only flukicides with a milk withhold that can be used during lactation are albendazole and oxyclozanide. These will target the adult fluke over 10 weeks of age but are not effective against the immature stages. Therefore if there is very heavy infection repeat treatment may be required.
Treating at dry off avoids milk discard and allows the use of products that can treat the immature stages of fluke, such as triclabendazole which will target fluke from 2 weeks of age. This should only be used during the high risk periods of infection such as now, as there is reported resistance.
It should be given 2 weeks after housing for fluke to be the correct age
•If cattle are housed after treatment, there is a very low risk of picking up new infection until they are turned out again. If cattle are turned back out after treatment, use tactics such as moving them to low-risk areas or fencing off wet areas
•If cattle remain on highly contaminated pasture, monitoring for infection is essential, as further treatments may be needed
Flukicides only kill the fluke present in the animal at the time of treatment and have no persistency of action, hence why reinfection can easily occur
•Prevention should be focused on pasture management and targeted fluke treatment
Please speak to your routine vet if you have any questions about fluke on your farm.
Katharine Benjamin, Synergy Veterinary Surgeon