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Vigilance Required On Parasites

29 January 2015

Sheep across the UK may be susceptible to a variety of parasites after a mild and wet autumn and early winter, says a national animal health monitoring groups telling farmers to plan ahead for next year.

The generally unsettled and mild theme of October continued through most of November, with only short periods of drier weather, says the National Animal Disease Information Service (NADIS). 

Review Flock Health Plan Now

Winter is a good time to review the parasite control plan for the forthcoming grazing season with your veterinary surgeon, advises NADIS.

'Safe grazing' available for ewes and lambs at turnout (e.g. last year's pastures grazed by cattle and re-seeded pastures) should be planned and utilised in a strategic manner to reduce reliance on anthelmintics to control internal parasites. In midsummer, silage aftermaths should be grazed by weaned lambs to reduce parasite challenge.

  • Winter 2014/5 was predicted to be a low/moderate risk year but disease may still occur on many farms unless control measures are implemented.
  • Chronic liver fluke in sheep peaks in the late winter/early spring.
  • Not all sheep with a significant fluke infestation show classical 'bottle-jaw' so now is the correct time to check faecal samples for eggs.
  • Low scanning rates and high barren rates may have been caused by liver fluke. Liver fluke may cause scanning figures to be up to 30 per cent lower than normal.
  • Sheep on farms with a history of acute liver fluke disease will already have been dosed with a flukicide, such as triclabendazole, effective against developing flukes from several days old.
  • All efforts must be taken to reduce reliance on triclabendazole by husbandry measures and the use of other treatments when appropriate.
  • Closantel and nitroxynil are very effective against immature flukes from around 7 weeks post infestation and should be used for the treatment of chronic fasciolosis.
  • Sheep should always be moved to clean pastures after treatment; supplementary feeding may be necessary to restore body condition.
  • Albendazole and oxyclozanide are effective from 10-14 weeks post infestation and can be used when treatment is recommended to remove adult flukes in late spring (often in May).
  • Quarantine treatments must be carefully considered for all introduced sheep and cattle.

What if I'm in a Low Risk Fluke Area?

In low risk areas, if animals have not been treated, then faecal samples from around 10 ewes will identify patent fluke infection acquired during the autumn and indicate the need to treat the group.

Not all sheep with chronic fluke present with 'bottle-jaw'.


Sheep affected by chronic liver fluke show significant weight loss. Note the adult flukes visible on cut section of the liver.

Foetal resorption (lower foetus) caused by liver fluke disease. This ewe would have produced a single lamb instead of twins.

Watch out for: Parasitic gastroenteritis (PGE) in fattening lambs and yearlings

The continuing mild weather may lead to the risk of PGE in store lambs and yearlings throughout the winter, particularly on paddocks heavily contaminated earlier in the season by grazing lambs.
This risk period can continue into February if mild weather conditions persist. The need to dose out-wintered store or replacement lambs during the winter can be reliably assessed by monitoring pooled faecal egg counts.

Watch out for: Lice in sheep

  • Louse populations are highest in sheep during late winter.
  • Spread occurs by close contact.
  • Lice infestations are widespread in most sheep flocks.
  • Use of plunge dipping for other reasons, such as control of sheep scab, cutaneous myiasis and headfly problems, also effectively controls louse infestations.
  • Louse infestations can also be controlled with topical application of high cis cypermethrin or deltamethrin best used soon after shearing.

Louse populations are highest during late winter and may cause disrupted feeding patterns, fleece damage/loss, and self-inflicted trauma.

Poor flock husbandry - heavy louse infestation affecting a hogg in poor condition.

Local farm conditions may vary so consult your veterinary surgeon. Parasite control should be part of your veterinary health plan.

NADIS hopes that you have found the information in the bulletin useful. Now test your knowledge by enrolling and trying the quiz. You will receive an animal health certificate for this subject if you attain the required standard.