Liver Fluke

Liver fluke are a common, very destructive parasite of sheep and cattle, with great potential to rob animals of productivity and inflict economic loss. Fluke have become well established throughout the North Island and the Northern and Western regions of the South Island. 

As more stock are moved around the country, the distribution and prevalence of liver fluke is expected to continue to increase.  Given this fact, it is vital that farmers consider the best way to prevent production losses by controlling existing fluke infections now.

Some stages of liver fluke infection are more hazardous to cattle health and farmers’ profits than others.  Bile duct stage fluke (adults and immature fluke more than 8 weeks of age) are far more likely to reduce productivity than immature fluke less than 8 weeks of age.

The reason for this is apparently because once fluke reach the bile duct, they become avid blood suckers.  Above all other factors, it is the loss of red cells and plasma due to bile duct stage fluke that accounts for the productivity losses typical of fluke infection.

The result of this is that the host animal compensates for the loss of red cells by making more of them, thereby diverting its energy and protein from productive purposes such as growth and milk production.

Often low infections of liver fluke produce little, if any, obvious symptoms.  Nonetheless, such subclinical infections can adversely affect feed conversion, weight gain and other productivity measures.  In addition, subclinically infected animals which remain untreated continue to contribute to pasture contamination by passing fluke eggs in the faeces

 Since infected cattle don’t use feed to best advantage, it takes more time and money to achieve the same weight gain or milk production.

The life cycle of F. hepatica is a complex one which requires an intermediate host, a snail of the Lymnaea species.  Within the animal the cycle takes 3-4 months to complete and commences with cattle (or sheep) eating the immature stage encysted on grass.  This stage then migrates to the liver for further development before settling in the liver bile duct to become an adult fluke laying eggs which pass out onto the pasture to start the cycle all over again.  Adult fluke may live in the bile duct of the animal for long periods of time.

The seriousness of infection depends upon the number of fluke larvae swallowed over a short period, or accumulated over time.

It is often very difficult to diagnose a liver fluke problem in cattle.  Even heavily infected cattle may not show clearly defined symptoms.  However now there are new blood and milk screening tests available from your Vet which can be used to assess the level of larval infection for necessary individual animals and so help with treatment decisions.