Farmers need to be prescriptive when it comes to selecting the correct wormer this summer with many farms experiencing mixed worm infestations and early fluke also a concern in some areas.

That was the message from the latest Parasite Watch which points out the importance of getting on top of these as soon as possible and using required treatment immediately.

Data from Parasite Watch – a real-time parasite monitoring service from Zoetis which gives an indication of the risk of high egg counts by showing the potential for larval development on pasture – has found positive fluke samples detected by Copro-Antigen tests in addition to high roundworm counts via Faecal Egg Count (FEC) tests. These mixed burdens make it important farmers know which worms are present and causing production losses on their farms so they can use the appropriate product, says Zoetis vet Dr Dave Armstrong.

“It is quite early to be seeing fluke detected by Copro-Antigen tests as they can only be detected from six to eight weeks of age. These test results mean the early immature fluke would have started infecting ewes and lambs back in May, which is a lot earlier than usual.

“With us seeing some high counts in the South West, this may just be the tip of the iceberg, as although there are not many cases reported, there may be a high level of infection.”

Two farms in Carmarthenshire have seen high fluke counts with cases also being reported in Worcestershire and Devon.

He added: “The mild winter and warm spring combined with the wet weather has provided perfect conditions for fluke and their host the mud snail. This is why we are seeing these early cases.”


Timing is everything when it comes to fluke control in sheep as it is the immature fluke that can cause the most damage as they migrate through the liver. A heavy burden can lead to sudden death, due to damage or by predisposing them to clostridial disease.

Other symptoms of acute fluke include:

  • Rapid loss of body condition and poor coat quality, despite adequate nutrition
  • Severe depression
  • Inappetence
  • Weakness


When selecting treatment options, farmers need to consider various things including:

  • Age of fluke – Many fluke treatments focus on killing egg-laying adults, meaning most immature fluke will still be present and causing damage. These will develop into adult fluke causing more damage for the sheep.
  • Efficacy of the product – Triclabendazole is the only ingredient effective against fluke from two days old. Products, such as closantel and nitrozynil are effective on fluke over six weeks old. However, their efficacy at this stage in sheep is only 50-90% effective compared to the 99-100% effectiveness of triclabendazole1.
  • Whether you have a mixed worm burden. Using a broad-spectrum combination product, such as Cydectin® TriclaMox®, which contains moxidectin and triclabendazole will be effective against worms for up to eight weeks and is also effective against immature fluke.