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The complicated story of fluke


Animals develop immunity to lungworms and gut worms, but do not develop immunity to fluke so they always need to be considered when housing all classes of cattle. Martina Harrington, Teagasc Cattle Specialist & Dr. Orla Keane, Teagasc Researcher have more information on fluke and how to prevent it.

Work in Animal Health Ireland (AHI) has shown that fluke could be costing you €70 per finished steer in lost performance if not treated correctly. While animals will develop immunity to lungworms and gut worms, they do not develop immunity to fluke, so they always need to be considered when housing all classes of cattle.

Once housed, animals cannot pick up any more fluke or worms so this provides us with an opportunity to “clean out” the animal. This will allow the animal to perform to its optimum while also ensuring the animal is not a source of infection onto pasture next year and thus reduces the infection pressure in the next grazing season. 

Warm wet summer

The summer of 2020 has been warm and reasonably wet, which are the ideal conditions for fluke to thrive, even on drier farms with low incidents of fluke. Each year, the Department of Agriculture, Food and the Marine (DAFM) in collaboration with Met Éireann advises farmers of the predicted risk of disease caused by liver fluke infection in livestock. This forecast is based on meteorological data gathered between May and October by Met Éireann. This report should be out soon here

That is why this year you need to pay particular attention to the control of fluke and ensure you get your housing treatment right. To do that you need to understand the different stages of fluke while it is in the animal.

The stages of fluke in your animal

  • Once eaten the larvae are freed from a protective cyst and bore through the intestinal wall and move into the liver. This can take 2 weeks.
  • In the liver the immature fluke burrow through the liver, severing blood vessels and destroying liver cells for 8-10 weeks. The level of damage is dependent on the number of fluke in the liver.
  • The immature fluke then move into the bile duct where they mature and start to produce eggs which are passed out in the faeces. In the bile duct they feed on the blood of the animal. In heavy infections they can cause anaemia.

These different stages are hugely significant when we decide what products we are going to use.

Active ingredients

There are 7 different active ingredients that control liver fluke, see the table below.

An active ingredient is the ingredient in the product that kills the parasite. The same active ingredient can be in several different products e.g. Endofluke and Fasinex both contain the active ingredient triclabendazole. It is the triclabendazole that kills the fluke so they are essentially the same.

The different active ingredients kill fluke at different “ages”. From a farmer point of view it is the age at which each product kills the fluke that is important and this is dependent on the length of time the parasite is in the animal as explained above.

  • early immature fluke (1 to 5 weeks)
  • immature fluke (6 to 9 weeks)
  • adult fluke (>10 to 12 weeks)

Table 1 List of Active Ingredients that kill fluke

Note some of the products in the Table are combination wormers/flukicides, for this article we are concentrating only on fluke.

Treatment of Fluke

Triclabendazoles control fluke from 2 weeks after they are ingested by the animal, so these are early immature fluke right up to the adults. If we use triclabendazole 3 weeks after housing we will kill all the fluke in the animal, assuming you don’t have resistant fluke on your farm.

Closantel, Rafoxanide and Nitroxynil will kill any fluke that are over 7-8 weeks of age, depending on the product. So any younger fluke will survive and be able to grow and mature all the while damaging the animal’s liver. Therefore, if I use Trodax (nitroxynil) after my animals are housed for two weeks, I will have to re-treat in 5 weeks’ time when the early immature fluke reach 7 weeks of age to kill them.

The Albendazoles, Clorsulon, and Oxyclozanide, will only kill the mature fluke, these are the fluke that have left the liver and reached the bile duct. These adult fluke were eaten by the animal 10-12 weeks ago. So products with these active ingredients will not kill the fluke that are burrowing around in the liver.

As the liver is the power house of weight gain in cattle when it is damaged or not functioning properly you can severely reduce animal performance. This is particularly important for famers who are feeding high quantities of meal. So you need to get it right.

You often hear of farmers housing animals and not treating until Christmas so they can use a flukicide that only kills adults. Are they taking into account the damage being done in the meantime? Are they taking into account potential loss in performance? This strategy may be okay on dry farms with very light fluke infections but would be very questionable on farms with heavy infections.

You also hear of people using a Nitroxynil based flukicide at housing as they think it kills all the immature fluke, now we know it doesn’t, it kills anything eaten over 8 weeks ago. So you need to sit down and work out a programme that suits your farm, taking into account the expected level of infection on your farm and the DAFM forecast. Use your Teagasc advisor!

How do you know if your dosing programme is working?

There are reports of resistance to Triclabendazole but we are unsure of how wide spread it is. If using products with this active ingredient you need to ensure it is working.

AHI Beef Health Check

A significant number of the meat processers have signed up to the Beef Health Check Programme. This is a process whereby a vet looks at the liver and lungs of your animals on the factory line and categorises the liver as listed below. If you are sending your animals to a participating factory you get this Beef Health Check report or you can look it up on ICBF by looking under services and AHI Animal Health, then click on the Beef Health Check. This report will tell you if the cattle had:

  • Normal Liver
  • Liver damaged by fluke but no live fluke detected
  • Liver damaged by fluke and live fluke present
  • Liver other damage
  • Liver Abscess

The AHI website has leaflets on how to interpret the report along with further information on the control of fluke, view them here

Ask the vet in the factory/abattoir to check the livers for you

If you are sending animals for slaughter to a meat factory / butcher that are not participating in the Beef Health Check programme then ask the vet who is on duty on the day doing the post mortem inspection to give you the details of any liver damage for your stock. 

Take faecal samples and submit to laboratory for egg testing 

This test will not detect early immature or immature fluke. Only adults that have reached the bile duct lay eggs. Also adult fluke intermittently lay eggs so you need to ensure to take samples from at least 10 different animals and from different spots in the dung pat. Use this information along with the history of the farm when interpreting your results.

Dr. Orla Keane, researcher in Animal Health with Teagasc has recorded a very informative short video below, in association with AHI, on the interpretation of faecal egg sample results which you may find useful. 

Check any sheep livers

During the year if you want to keep an eye on the fluke status on the farm, as lambs are killed throughout the year, have their livers checked to see if they have fluke. If they have you can assume your cattle will have fluke also if they are grazing the same pastures for the same length of time.

Fluke has a complicated story, but if you think about it and discuss with your vet or advisor, you can be successful in treating it correctly and ensuring top performance in your animals this winter.