Liver fluke affecting your stock?
Are you getting kill sheets back with live liver fluke present? If so, it is time to act to reduce the damaging effects of the fluke on the liver.
Drought conditions encountered this season have encouraged stock to graze into wet areas (if anything was still wet?) leading to potentially high intakes of liver fluke larvae from the pasture.
Liver fluke can be responsible for:
- Reduced reproductive performance
- Increased culling
- Decreased cull weights
- Reduced milk production
- Reduced growth rates
- Reduced wool yields
- Potential immune suppression
Once liver fluke has been brought onto a farm it is impossible to eradicate if the mud snail intermediate host is present. Therefore, the goal is to prevent it from establishing in the first place. Good biosecurity measures including quarantine drenching will prevent the establishment of liver fluke on most farms if carried out appropriately and drench checked.
The life cycle requires an intermediate mud snail host. This is a multiplication stage for the fluke cycle and weather conditions that favour snail survival are related to high infection rates in farm animals. Many different species can be infected with fluke including people. It takes 10-12 weeks from the time the juvenile fluke enters the liver to the time they become adults laying eggs. This whole life cycle can be completed in 4-6 months with the adult fluke surviving for a year or two in cattle and much longer in sheep.
The aim of any liver fluke control program revolves around three main areas:
- Reduce exposure of stock to areas prone to harbouring potentially high levels of infective larvae on pasture.
- Reduce access to the intermediate host snails (difficult to achieve)
- Strategic use of drenches
Where feasible, fencing off swamps, dams and drains would be effective and having water troughs in all paddocks would also reduce the intake of larvae. Obviously, this is not feasible on many farms which leaves us with the strategic use of drenches to control the population of liver fluke from year to year.
The immature migrating liver fluke has the greatest economic impact on production, compared to the adult liver fluke which reside in the bile ducts of the liver, therefore, controlling the number of larvae eaten has to be the priority.
Immature fluke are more difficult to kill as they migrate across the liver causing significant damage. Make sure the products you are using will control the stages you want. Nitroxynil (fattening cattle only) and Triclabendazole are effective in early immature flukes 2 weeks after infection, while Closantal and Clorsulon are effective 8 weeks after infection. The BZ drench family has some efficacy against adult flukes at higher dose rates. There is worldwide concern about fluke resistance to Triclabendazole and it is diagnosed in New Zealand so a drench check is advised when using this product.
Key Points to remember
Fluke eggs do not develop significantly or hatch below 10 degrees. Therefore, in many parts of the country, fluke infective stages will not be ingested by stock again till spring/summer. Adult liver fluke are prolific egg producers. If we can limit the number of adult liver fluke in stock at the start of spring we can reduce the level of infection in the subsequent season