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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - February 2018

18-02 PF Capture


December started cold and frosty becoming milder, followed by a cold wintry spell, which brought widespread frosts, and snow for some, especially the Midlands.  It then became mild from the middle of the month ending with further snow for some, mainly in the north.  The UK mean temperature was 4.1 °C, which is 0.2 °C above the long-term average. UK Rainfall was 99% of average, being drier than average for much of eastern Scotland and north-east England, but wetter than average in East Anglia and the south-east.


February Parasite Forecast/Update


Review of parasite control plans

  • If not already done, now is an appropriate time for farmers to review parasite control plans for the forthcoming grazing season with their veterinary advisers.
  • Identify parasite risk by mapping the farm to determine both previous and future use of pastures, particularly use of aftermaths and which classes of stock will be moved there.
  • This can be done by making use of the new parasite control planners available through veterinary practices participating in the NADIS parasite control initiative.

18-02 PFF1

NADIS Sheep Parasite Control Planner
  • For worm control: identifying 'safe' grazing for ewes and lambs available at turnout (e.g. last year's pastures grazed by cattle or re-seeded pastures) will avoid the risk of disease due to Nematodirus battus infections in young lambs in spring.
  • In mid-summer, silage aftermaths can be utilised to reduce reliance on wormers used to control internal parasites in weaned lambs.
  • With first year grazing calves, decide if the parasite control plan will be strategic (e.g. grazing management/early season suppression) or therapeutic with regular monitoring and treatment intervention where needed.

18-02 PFF2

NADIS Cattle Parasite Control Planner for 1st Year Grazers


Liver Fluke

Continue to check for chronic liver fluke in sheep.

  • This winter has seen a high-risk for liver fluke disease in North, West and Central Scotland, West Wales, and parts of Cornwall this autumn; with "medium-risk" in Eastern Scotland, and areas of North and South West England
  • Chronic liver fluke will be encountered in sheep flocks during late winter/early spring unless action is taken now.
  • Poor scanning results may be the first indication that there is a liver fluke problem on the farm and may be limited to only one group of sheep depending upon its autumn/winter grazing.

18-02 PFF3

Poor scanning results (image shows resorption of lower foetus) may be the first indication that there is a liver fluke problem on the farm.

  • Fluke-infected sheep can show progressive weight loss, weakness, lowered appetite, emaciation and visible pallor of the mucous membranes,
  • Be aware that not all sheep with fluke infestation develop sub-mandibular oedema or "bottle-jaw".
  • Fluke infections can be confirmed by checking for the presence of fluke eggs in faeces or by using the faecal antigen ELISA test which detects digestive enzymes that are released into the bile by migrating (late immature) and adult flukes in the faeces.
  • Care must be taken to ensure that all sheep are drenched correctly especially when working with sheep in a pen rather than a race.
  • All efforts must be taken to reduce reliance on triclabendazole by husbandry measures, and by using other flukicides as appropriate.
  • Closantel, nitroxynil, oxyclozanide and albendazole (at the fluke dose rate) are all effective against adult flukes, which are present at this time of year.
  • Take care not to overdose with some flukicides, which can have lower safety margins than other wormers.
  • Weigh a representative number of sheep to gauge the correct bodyweight range within the group/flock.  If there is a significant difference between breeds, weights or ages, separate and drench as several groups.
  • Limiting pasture contamination with fluke eggs now from patent infections will reduce subsequent fluke challenge later in the year.

18-02 PFF4

Sheep affected by chronic liver fluke show significant weight loss. The mature flukes live in the bile ducts but are shown here on the surface of the liver. Compare with a normal sheep's liver (below).

18-02 PFF5

Worm Control

  • Store lambs and yearlings may continue to be at risk from worm infections.
  • The need to dose out-wintered store or replacement lambs can be reliably assessed by monitoring pooled faecal egg counts.
  • As lambing time approaches, of impending consideration is what to advise on choice of wormer, and when and how frequently to treat ewes during, or after lambing.  Such treatments are aimed at controlling pasture contamination from the so called "periparturient rise" (PPR) in worm egg output.
  • With the emergence of anthelmintic resistance (AR) in sheep nematodes, the continued effectiveness of dosing ewes at lambing time may influence recommendations on both product choice and application particularly when it come to the use of long, or short, acting wormers.
  • The current recommended strategy for ewe treatments is therefore a compromise between reduction in pasture contamination for the subsequent grazing lambs, and avoiding high selection pressure for AR.
  • SCOPS currently recommend two possible options:
    • Leave a proportion of the ewes untreated or;
    • Treat early in the post-lambing phase, especially with long-acting formulations of moxidectin, to ensure that ewes become re-infected with unselected parasites before their immunity is fully restored.
  • There are no hard and fast guidelines as to how many ewes to leave untreated.  It has been suggested that leaving about 10% of the flock untreated will be sufficient to provide a large enough dilution effect to delay selection for AR strains. This can be achieved be leaving single-bearing ewes and/or a proportion of ewes in good body condition untreated.
  • Further details can be found on the SCOPS website at

Sheep Scab

  • Sheep scab is typically encountered during the autumn/winter months from September to April.
  • Sheep have disturbed grazing patterns and are observed kicking at their chest 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.
  • Early disease is often confined to the back and withers, but as the disease progresses wool loss extends down the flanks and the lesion is surrounded by an area of inflammation and serum exudation, with the skin often thrown into thickened corrugations.
  • Sheep scab can be controlled 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, and recent reports of ML-resistance in scab mites, it is important to ensure injectable scab treatments are given correctly.
  • Plunge dipping in diazinon is an alternative and effective treatment option for most ectoparasitic infestations of sheep including sheep scab, but can present problems during the winter months on both welfare, and correct dip disposal grounds.
  • For more information on scab, and other ectoparasite treatments, consult the product literature, or the SCOPS website for specific product recommendations.

18-02 PFF6

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.


Liver Fluke

  • Cattle grazing potentially fluke infected pastures, especially those in high fluke-risk areas, should be checked for the presence of fluke eggs in faeces and if positive, treated and moved to fluke-free pastures.
  • Cattle with chronic liver fluke infection typically show signs of chronic weight loss and diarrhoea.
  • More than 25% of bovine livers are condemned because of liver fluke damage.
  • If slaughterhouse results are positive seek advice regarding treatment and control measures that need to be implemented.


18-02 PFF7

Out-wintered cattle should be checked for the presence of fluke eggs in faeces.

18-02 PFF8

This bovine liver at the slaughterhouse shows extensive liver fluke damage

Worm Control

  • Any cattle not dosed on housing in the autumn, may be at risk from type II ostertagiosis towards the end of the housing period.
  • Type II ostertagiosis presents as intermittent diarrhoea with loss of appetite and rapid loss of body weight.
  • On farms with a history of lungworm, vaccination of all calves offers the best form of protection against lungworm disease.
  • As the lungworm vaccine is a live attenuated vaccine with a short shelf-life, ordering and administration needs to be planned well in advance of turnout.
  • For vaccination to be effective, all calves over two months-old should be given two doses of lungworm vaccine four weeks apart, with a second dose at least two weeks before turnout.







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