Many challenges are facing livestock producers this winter due to the seemingly endless wet weather. One potential health issue to which all sheep and cattle producers should be giving consideration is liver fluke.
Immature liver fluke (called metacercariae) accumulate on pasture in large numbers from late July. This year’s weather will undoubtedly mean that levels of metacercariae on pasture will be particularly high. When eaten by grazing cattle and sheep these immature fluke migrate to the liver and develop to maturity. Affected animals can show signs including weight loss, anaemia and soft swelling under the jaw. Particularly in sheep, migrating immature fluke can cause sudden death.
One complicating issue with the treatment of liver fluke infection is that different drugs kill fluke at different stages of maturity. Drugs like clorsulon (present in Ivomec super and Animec super), oxyclosanide (present in Zanil and Levafas diamond) and albendazole (present in Albex and Endospec) only eliminate adult fluke, which is fluke ingested by the animal at least 10 weeks ago. Other drugs kill mature fluke and immature fluke that infected the animal more than about six weeks ago. Examples are nitroxynil (present in Trodax) and closantel (present in Flukiver and Closamectin). Triclabendazole (Fasinex and Triclafas) is effective against all fluke from two weeks after infection.
As metacercariae will still be present on pasture, there is a case for treating sheep still outside with triclabendazole. Unfortunately, triclabendazole resistance is relatively common and producers using triclabendazole alone should be aware of this.
It may be more appropriate to treat animals that have been housed for a period of time with flukicides other than triclabendazole. If animals have been housed for 10 weeks or more all fluke should be mature enough to be susceptible even to the drugs that only kill adult fluke.
Our wet year also means that cattle and sheep are also at risk from rumen fluke. If it is suspected that this parasite is affecting stock remember that oxyclosanide (present in Zanil and Levafas diamond) is the only drug that is effective against it.
If animals are going to slaughter it can be useful to request information from the meat plant about the level of liver and rumen fluke infection in your animals.
In summary, the prolonged wet weather poses various health risks to stock this winter. Stock keepers should discuss appropriate parasite treatments and vaccinations with their vet to try to protect their animals.