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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - January 2017

PF Capture

The weather in November started off quiet and mild in the south, but cold bright weather spread from the north followed by some snow even for many low-lying parts of Scotland and northern England. Thereafter, it was generally unsettled with several bright showery days. Storm Angus brought wet and windy weather and problems with flooding in the south-west, and a further depression brought heavy rain and more widespread flooding on the 21st of the month. High pressure brought generally dry, settled and cold weather for the last week, with frequent sunny spells for most parts. Temperatures were 1.3 °C below the 1981-2010 long-term average. The negative temperature anomaly was generally larger by night than by day, and largest in Scotland. Rainfall was 89% of average, and it was a dry November over much of Wales, Northern Ireland and central and western Scotland, but most of England had near or rather above average rainfall.(


January Parasite Forecast/Update



  • Plan now.  Winter is a good time for farmers to review the parasite control plan for the forthcoming grazing season with their veterinary surgeon.
  • "Safe grazing" available for ewes and lambs, (or autumn born calves) at turnout, should be planned and utilised in a strategic manner to reduce reliance on anthelmintics to control internal parasites.
  • Safe grazing includes last year's pastures grazed by cattle (or sheep); re-seeded pastures, or from midsummer onwards, silage or hay aftermaths.

Watch out for chronic liver fluke in sheep and out-wintered beef cattle this winter

  • The risk of liver fluke disease has been predicted to be high in Scotland, north-western regions of England, and north Wales, with a moderate to high risk in south Wales and south-west England. The high-risk warning follows a year where there was a high prevalence of liver fluke disease leading to pasture contamination with eggs last winter and production losses due to chronic liver disease will result unless farmers continue to implement control measures.

COWS and SCOPS recommend these simple steps to identify risks from liver fluke on farms:

1.  Identify high risk fluke areas and consider if grazing these pastures can be avoided. Practical steps include fencing off wet areas, attending to leaking troughs and pipes, drainage or even consider housing early.

2. Ask for abattoir feedback on any liver rejections which provides a warning that there may be a fluke problem on a farm.

3. Investigate losses by post-mortem examinations when the opportunity arises, or with FECs. Ideally herds and flocks should be monitored before a flukicide is used unless there is a history of fluke infection on the farm.

Signs of Liver Fluke

  • Chronic liver fluke in sheep and cattle peaks in the late winter/early spring.
  • Affected sheep may show a progressive loss of condition, weakness, lowered appetite, emaciation, a brittle open fleece, and the development of anaemia characterised by pale mucous membranes.
  • Not all sheep with a significant fluke infestation show classical 'bottle-jaw'
  • Liver fluke may cause scanning figures to be up to 30% lower than normal with a much higher barren rate (2 per cent is considered a normal barren rate after two cycles).
  • Cattle with chronic liver fluke typically show signs of chronic weight loss and diarrhoea.
  • More than 25% of bovine livers are condemned because of liver fluke damage; positive results from the slaughterhouse should be discussed with your veterinary surgeon.

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Not all sheep with chronic fluke present with "bottle-jaw". Image courtesy of Phil Scott.
Sheep affected by chronic liver fluke show significant weight loss.  Note the adult flukes visible on cut section of the liver. Image courtesy of Phil Scott.
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Do not allow liver fluke infestation to undo a successful mating period. Image courtesy of Phil Scott.

Liver Fluke Control

  • At this time of year, efforts must be taken to reduce reliance on triclabendazole by husbandry measures and the use of other flukicide treatments when appropriate.
  • Closantel and nitroxynil are highly effective against adult and late immature flukes and should be used now for the treatment of fasciolosis in sheep in high fluke-risk areas.
  • Undosed beef cattle grazing potentially infected pastures, should either be treated or checked for the presence of fluke eggs in faeces.
  • Where possible, treated sheep and cattle should be moved to fluke-free pastures after treatment.
  • Supplementary feeding may be necessary to restore body condition before late pregnancy.
  • Where triclabendazole resistance is suspected, a fluke faecal egg count reduction test should be considered at 3-weeks post treatment. The alternative, is the coproantigen ELISA test, which can be used two to three weeks after dosing. Farmers should contact their veterinary practitioner for further advice where such drug resistance is suspected.
  • Quarantine treatments must be carefully considered for all introduced sheep and cattle.

Low risk fluke areas

  • In low risk areas, if animals have not been treated, then faecal samples from around 10 animals will identify patent fluke infection acquired during the autumn and indicate the need to treat the group.
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Out-wintered cattle should either be checked for the presence of fluke eggs or treated. Image courtesy of Phil Scott.

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

  • The short spell of mild weather in December 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 well into next year 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.
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Continuing mild weather may lead to PGE, especially from Trichostrongylus vitrinus, in store and replacement lambs this winter. Heavy infestations of this parasite cause black foetid diarrhoea (black scour) and rapid weight loss. Image courtesy of Phil Scott.

Watch out also for scab and lice infections in sheep

  • The symptoms of both sheep and lice can be similar and so diagnosis is important before advising on treatment.
  • For sheep scab, tests available include examining skin scrapings from suspect sheep or an antibody test on blood samples.


  • Sheep scab, caused by the presence of psoroptic mites, can be very debilitating with significant loss of condition, secondary infections and eventually deaths if not treated.
  • Remember also that sheep scab is notifiable in Scotland.
  • Sheep scab is typically encountered during the autumn/winter months from September to April.
  • Affected sheep may be restless, have disturbed grazing patterns and are observed kicking at their flanks with their hind feet and/or rubbing themselves against fence posts.
  • The fleece is wet, sticky, yellow, and frequently contaminated with dirt from the hind feet.
  • Typically, after eight weeks' infestation or so the hair loss on the flanks may extend to 20 cm diameter surrounded by an area of inflammation and serum exudation. The skin is often thrown into thickened corrugations.



Early sheep scab - rubbing causing breakage of wool over the chest wall. Image courtesy of Phil Scott.

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Advanced sheep scab -there is extensive fleece loss over the chest which is wet, sticky and yellow at the edges due to serum leaking from the skin. Image courtesy of Phil Scott.


  • Like sheep scab, louse populations are highest in sheep during late winter.
  • Lice infestation is commonly mistaken for sheep scab and vice versa.
  • Spread occurs by close contact with other sheep.
  • Infestations of chewing lice are widespread in most sheep flocks. Sucking lice are not a problem in the UK.



Louse populations are highest during late winter and may cause disrupted feeding patterns, fleece damage/loss, and self-inflicted trauma. Image courtesy of Phil Scott.
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Poor flock husbandry - heavy louse infestation affecting a hogg in poor condition. Immediate treatment is necessary for welfare reasons. Image courtesy of Phil Scott.

Treatments for Scab and Lice

  • Plunge dipping in diazinon is an effective control for sheep scab and louse infestations (as well as other ectoparasite infections including blowfly strike and headfly problems), and may be the most cost-effective and practical option, provided there are no short-term welfare or safety concerns.
  • Sheep scab can also be treated (or prevented) by administration of an injectable macrocyclic lactone (ML). Treatment requires either a single, or repeat injection 7-10 days apart, depending of the product and active ingredient.
  • Because of the growing concern over selection of ML-resistance in roundworms, it is important to ensure scab treatments are given correctly following current SCOPS guidelines.
  • Louse infestations can also be controlled with topical application of high cis cypermethrin or deltamethrin.
  • For more information on ectoparasite treatments consult the product literature, or the SCOPS website ( for specific product recommendations.

Ectoparasite infections in cattle


  • Like sheep, cattle can be infested with lice or mange mites, particularly during the winter months and early spring.
  • Low burdens of lice are very common in the coats of cattle during the winter months and should not necessarily be considered of significance. However, populations can increase rapidly causing intense itching, or anaemia if sucking lice are present.
  • Heavy louse infestation may be a sign of other underlying conditions and an indicator of ill-thrift.
  • A range of pour-on or spot-on synthetic pyrethroid products (containing alpha-cypermethrin, deltamethrin or permethrin) and macrocyclic lactones are commonly used.
  • Note: injectable macrocyclic lactones are more effective against sucking lice and may have only limited activity against chewing lice.


Heavy louse infestations in cattle may be a result of ill-thrift or other underlying causes. Image courtesy of Phil Scott.

Mange Mites

  • The commonest mange affecting cattle is chorioptic mange, which occurs most often in housed cattle on the feet, legs, base of the tail and udder.
  • Only a small number of products are authorised for use against chorioptic mange. Permethrin or topically applied (pour-on) products are generally effective.
  • Psoroptic mange has only rarely been reported in the UK.  Infection causes intense itching, crusting and hair loss.
  • Treatment is difficult and requires veterinary advice. (For more information see the COWS website (

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

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