Michael Conroy, Teagasc drystock advisor
Liver fluke is caused by a flat-like worm that requires a mud snail to develop. High rainfall and warm conditions are an optimum environment for mud snails. With the warm, wet weather we have had since August, there is likely to be a high incidence of liver fluke in sheep.
Liver fluke life cycle
The adult fluke in sheep produce eggs which are passed onto the pasture. In warm, wet conditions, these hatch out, pass through a mud snail to produce larvae which are then picked up off the grass by the sheep.
Once the fluke larvae are eaten by the sheep, they burrow from the intestine through the liver causing considerable damage and end up in the bile duct of the sheep as adult fluke.
After the fluke larvae are picked up from the pasture, they develop into three stages, namely: early immature fluke (weeks one-to-five); immature fluke (week six-to-11) and mature fluke.
12 weeks after the sheep pick up the fluke larvae from the pasture, the life-cycle is complete and the adult fluke start to pass eggs onto the pasture.
2 types of liver fluke diseases
Firstly, acute fluke occurs as a result of large numbers of immature fluke burrowing through the liver of the sheep and can lead to sudden death.
And secondly, chronic fluke arises due to fluke sucking blood in the liver. Signs include: loss of condition; anaemia paleness around the eye; and swelling (bottle jaw) due to retained fluids. If not treated the animal will die.
Treatment
There are products on the market that control immature and adult fluke and other products that only treat adult fluke.
From now until January, the greatest threat is from immature fluke and a product should be used that is effective against this form of fluke.
Farmers are confused when ewes die from fluke even though they have been treated. This is due to using a product that only controls adult fluke and the problem is immature fluke.
In other farm situations, there is resistance to some products which make them ineffective. Consult your vet to draw up an effective control programme on your farm.
Aim of treatment
In the autumn, aim to prevent immature fluke from developing following ingestion and prevent sudden death due to acute fluke.
In the winter, aim to kill adult and immature fluke and prevent liver damage and ill-thrift. In spring / early summer, aim to remove adult fluke and reduce summer infection of snails.
Other considerations
Fence off wet areas to reduce access to contaminated pasture. Get feedback on the level of contamination when slaughtering ewes/lambs.
And, get faecal counts done to establish the level of adult fluke contamination, but remember this will not establish the level of immature fluke which cause sudden death.