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Dec 16

Fluke in the Beef Industry

What is fluke?

Fluke is a liver parasite found in cattle, sheep, goats, horse, deer and man. Adult fluke lay eggs which pass onto pasture (hundreds per day), eggs hatch in spring when the mean temperature is over 10C and release miracidia which penetrate a mud snail. They develop in the snail and emerge as a cercariae which encysts on the grass as a metacercariae. Infection of one snail can produce over 600 metacercariae over 3 months. After ingestion of metacercariae by the cow the immature fluke migrate through the gut wall and penetrate the liver. They then tunnel through the liver for 6-8 weeks before entering the bile ducts as mature adults. Time from infection to becoming an egg laying adult is 12 weeks. There is also little to no development of immunity.

What are the risk factors?

If you have had fluke previously (one adult fluke can produce 30 million infective metacercariae) – the challenge can increase year on year. An environment where the mud snail will thrive, such as; around streams and ponds, leaky water troughs and wet poached areas all increase the risk. Equally weather conditions which favour the snails – a mild, wet autumn and winter followed by a wet summer will lead to a very high risk.

The types of infection

Acute fluke damage occurs 1-5 weeks after infection of the cow and is the result of damage caused by the migration of large numbers of immature parasites through the liver. This is normally seen in late summer and autumn but occasionally into winter due to animals ingesting large numbers of immature fluke off pastures. Sub-acute fluke damage leads to the loss of condition and performance during autumn and early winter and is due to the immature fluke damaging the liver as they migrate, normally 6-9 weeks after infection. Chronic fluke damage occurs when adult fluke feed and lay eggs in the bile ducts and this often occurs later in the autumn and winter and results in anaemia. Adult fluke consume half a ml of blood per fluke per day, and is shown as a loss of condition and bottle jaw. Because of the damage it also predisposes the animals to other diseases such as black leg, metabolic disease and parasitic gastroenteritis.

The cost of fluke

Industry as a whole: £13-15 million in 2011 for beef and sheep. 22% cattle livers rejected (£3million). To producers: £30-£200 per beef animal, cattle can take an extra 80 days to reach market weight if affected by fluke due to a reduced weight gain of 0.5-1.6kg per week. Losses are based on weight loss due to anaemia, poor performance, depressed appetite, reduced weight gain, increased barren rate, death and condemned livers.

Diagnoses and monitoring

Diagnoses and monitoring can be based on clinical signs including weight loss and ill thrift, sudden death, bottle jaw, anaemia and in extreme cases abdominal pain and respiratory distress. Fluke egg counts from faecal samples, blood samples and post mortems can all diagnose fluke infection. Feedback from the abattoir should be backed up with other tests as all liver disease is often attributed to fluke.

Managing fluke

Avoidance of fluke; avoiding flukey pastures and wet boggy areas within fields at peak risk periods can reduce the exposure of sheep and cattle. This may mean using temporary fencing around risky areas or in some cases avoiding whole fields or grazing areas. Increasing drainage, providing water troughs and ensuring they are not leaking! Keeping ducks to eat the mud snails

Treating fluke

Treatment needs to be based on the time of year and the age of fluke as different flukicides work at different ages. Before housing immature fluke will have been ingested at pasture, once housed no more can be ingested – therefore if we wait 10-12 weeks all fluke will be adult and we can use an adulticide fluke treatment.

Oxyclosanide, albendazole and clorsulon are best used after 12 weeks as they only kill adult fluke. Nitroxynil and closantel can be used to kill late immature fluke from 8 weeks of age. And triclabendazole can be used to treat early fluke from 2 weeks of age.

If not housing we need to be aware of the risk of reinfection and management tactics such as moving to low risk areas and fencing off risky areas should be utilised. In these animals a flukicide utilised against late immature fluke can be used twice throughout the winter to lower the risk of sub-acute and chronic fluke problems.

In spring in both housed and out-wintered cattle the use of an adult only flukicide product can be used to clear out adults and reduce the egg output on pastures after turnout. A faecal egg count can be performed to ensure this dose is necessary.

Resistance

Resistance is on the increase to flukicides. Triclabendazole resistance is a big problem in our area and this particularly a problem in sheep which are affected more by acute fluke due to the relative size of their liver. Triclabendazole should be reserved therefore for acute problems in sheep to reduce its use and reduce the selection pressure for resistance.

Alternating other drug use will also help to delay the development of resistance in these drugs.

Summary

Out-wintered cattle at risk now should be treated with a product with some activity against immature fluke (closantel or nitroxynil) this can be repeated in January to mop up current early immature fluke.

Housed cattle can be dosed with the same closantel or nitroxynil after 8 weeks of housing or albendazole, clorsulon or oxyclosanide 12 weeks after housing.

Treatment with albendazole, clorsulon or oxyclosanide in May will remove adults and decrease pasture contamination.

Permanent link to this article: http://www.tetheravets.co.uk/fluke-in-the-beef-industry/