Liver Fluke:

The life cycle of the liver fluke is such that each egg passed out by an infected animal has to develop for three months outside the cow or sheep before it is mature enough to infect other animals.

The development of fluke eggs outside the host will only take place at temperatures greater than 10 degrees Celsius and in boggy conditions. Once eaten by a cow or sheep the flukes migrate to the liver to cause either acute fluke (approximately four weeks after being eaten) or chronic fluke (twelve weeks after ingestion). Because fluke eggs only develop in warmer weather (summer months) it usually means that acute fluke is seen in autumn or early winter.

If treating sheep at this time of year we recommend a fluke drench such as Fasinex which is effective against both adult and immature flukes. Ewes should not be treated during the first forty days after tupping or at the same time as receiving copper injections or drenches. There are no fluke treatments with a nil milk withhold for cattle.

Liver Fluke in cattle (pdf 229)
Liver Fluke control in sheep (pdf 2.2mb)