Liver Fluke in Cattle

Written by Andrew Cribb, Director/Veterinarian of East Coast Farm Vets

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Liver Fluke Fasciola Hepatica, are flatworms that feed on the blood of their host and can destroy the liver of infected stock.

Their life cycle is complicated and involves numerous larval stages, water snails as intermediate hosts and can vary considerably in length, depending on environmental conditions.

Early immature fluke (2 weeks after ingestion) are crucial to keep under control as they travel through the liver and can cause more damage than adult fluke. Clinical signs observed range from anaemia and weight loss (<200 adult fluke) to sudden death (<1000 immature fluke).

Adult fluke live in the bile ducts, feeding on the blood of the host. The long-term effects can be significant, with each fluke consuming up to 0.5ml of blood per day. With hundreds of fluke in some livers, blood loss can become very significant.

Cattle are particularly prone to liver fluke infections because they often feed in the wet areas that suit the water snail immediate host and the infective fluke stage. Young stock is particularly at risk.

While the viruses (like parainfluenza) and bacteria (like Manheimia haemolytica) which cause

pneumonia circulate in all populations of sheep year-round, environmental and animal risk factors come together mainly in the summer months to trigger clinical disease.

A degree of immunity is acquired over time; however this is often associated with extensive prior damage to the liver. Unfortunately, this type of resistance is not a protective immune response, having little ability to control immature flukes. Although fluke numbers can be suppressed, liver damage and consequently production loss will occur.

Sheep on the other hand avoid wet areas but graze the grass lower and so therefore can pick up significant infection in contaminated pasture. Farms with persistent wet areas and those in parts of the country that experience long, hot summers are most at risk.

Periods of extended drought force sheep to graze contaminated wet areas, thereby greatly increasing the risk of infection. Sheep also develop little resistance to liver fluke meaning all age groups are susceptible to repeated seasonal exposure and therefore require treatment.

Other than monitoring stock for clinical signs or examination of the liver post-mortem, diagnosis can be achieved through blood testing (liver function, ELISA) and faecal egg counts.

Correct timing of treatment and product selection is based on the biology of the fluke and likely parasite challenge to stock. The two core treatments are in late autumn/early winter and late winter/early spring.

Cyclone Gabrielle and the challenge of getting stock to yards meant that some livestock may have missed treatment. Be on the lookout for increased health challenges as a higher parasite challenge could be present.

The spring treatment is an essential preventative treatment that helps to break the fluke life-cycle by removing any flukes that have infected the animals throughout the winter. By preventing the contamination of the pastures with fluke eggs as temperatures warm up, the snail intermediate hosts do not immediately become infected as they become active.

Spring treatment should therefore primarily target adult fluke however; the mild and wet winters of the East Coast mean fluke infection can continue throughout the year. As a result, consideration should be given to treating for immature fluke using a combination drench.

Contact your vet team to discuss the best options for treating liver fluke at their various larval stages.

This article was published in the Gisborne Herald on 14/06/25