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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - October 2017

17-10 PF Capture

The cool weather seen in late July continued into August, which was mostly cooler than average apart from a few warmers days in the middle of the month, particularly in SE England. The UK mean temperature was 14.5 °C, which is 0.4 °C below the long-term average.  Rainfall was generally above normal, with more than 150% of average in places, but south Wales and parts of eastern England were a little drier than average.

October Parasite Forecast/Update


Liver Fluke Forecast

17-10PF F1

  • Based on the cumulative wetness scores for each grid, a more detailed, fluke-risk map will be produced in November, with high-risk grid areas appearing red; medium-risk amber; and low-risk green.
  • Even within these grid areas, local conditions and individual farm circumstances can vary so contact your vet for further information and advice.


Liver Fluke

  • Industry representatives are urging farmers to consult their veterinary surgeons and SQP to develop their knowledge of liver fluke to ensure flock profitability and sheep welfare.
  • There was an increase in diagnoses of liver fluke disease at the start of this year and the risk of acute fluke is forecast to be high in some parts of Scotland and North Wales. It is therefore likely, that treatment for acute fluke will be necessary during October on farms in these regions, especially where there is a history of liver fluke disease.

Signs of acute fluke disease

  • Sheep with acute fluke infestation may simply be found dead without prior signs of illness therefore it is important to have all sudden deaths investigated to allow immediate preventive measures.
  • Post-mortem examination is essential to establish a diagnosis of acute fluke.
  • Less severe clinical signs include reduced grazing, rapid weight loss, weakness, abdominal pain, anaemia, and slow to gather.


17-10PF F2

Signs of subacute liver fluke diseases include rapid weight loss, poor fleece, and weakness.

17-10 PF F3

Anaemia (pale mucous membranes) caused by liver fluke disease

Fluke Control Measures

  • Liver fluke disease can be largely controlled by effective drugs administered at the correct time as part of the flock health plan.
  • Wherever possible, reduce the risk of fluke infection by keeping sheep away from potentially contaminated, poorly-drained areas of the farm.
  • Triclabendazole (TCBZ) is the drug of choice in cases of acute fluke disease because it is effective against very young immature fluke stages.
  • However, advice will also be needed where TCBZ-resistance has been previously suspected on farms and the effectiveness of fluke treatments monitored.
  • The coproantigen ELISA test can be used to monitor TCBZ efficacy two to three weeks after dosing, and farmers should contact their veterinary surgeon for further advice where drug resistance is suspected.
  • Later fluke treatments could use closantel or nitroxynil especially if TCBZ- resistance is suspected or proven on the farm.
  • Where these drugs are used then accurate dosing is essential as toxicity is possible.
  • Also, ensure all lambs are vaccinated against clostridial diseases because migrating flukes predispose to Black disease.

Parasitic Gastroenteritis (PGE)

  • PGE is likely to a problem on contaminated grazing in many areas as larval challenge continues.
  • On contaminated pastures, prolonged wet and mild weather will give rise to flushes of infective larvae on the pasture causing diarrhoea.
  • Outbreaks of trichostrongylosis are often seen from late October onwards in store and replacement lambs, and sometimes yearlings.
  • Heavy infestations cause black foetid diarrhoea (black scour) and rapid weight loss.
  • Monitor lamb liveweight gain or worm faecal egg counts (FEC) to determine the need for anthelmintic treatments.
  • Anthelmintic treatment of all breeding females pre-tupping is rarely necessary
  • Dosing all ewes pre-tupping may select for anthelmintic resistant strains.
  • In general terms, anthelmintic treatment should be targeted at leaner ewes, gimmers, or those sheep with "dags".  Treated sheep should form no more than 5% of the group.
  • Rams are often neglected at this time and a faecal worm egg count will decide whether a pre-tupping anthelmintic treatment is necessary.


17-10 PF F4

Poor fleece, low body condition and widespread "dags" two months post- weaning. Anthelmintic treatment should be targeted at such leaner ewes. investigate potential cause(s) if a high percentage of sheep (>5%) are in such poor condition despite good grazing.


Fluke Control

  • Cattle may also be at risk from liver fluke in "high-risk", and "medium-risk" areas this autumn.
  • In "high-risk" areas, grazing cattle may need to be dosed for fluke with a product with activity against immature fluke.
  • The choice of treatment in cattle will be influenced by risk of infection; meat/milk withdrawal periods; risks posed by other parasites; and ease of administration.
  • Whilst triclabendazole is the most effective against early immature fluke, because acute fluke is rare in cattle, there are several alternatives available, so seek advice and base treatments on local farm conditions and the NADIS fluke forecast.
  • If treated, cattle should be moved onto fluke-free pastures as soon as possible.

Dosing on housing

  • Growing cattle housed after their first or second season at pasture should be treated with products containing either a Group 3-ML or Group 1-BZ anthelmintic at housing, which are effective against inhibited worm larvae.
  • Group 3-ML pour-on preparations have the added advantage they are also effective against both sucking and chewing lice.
  • There are benefits on growth and feed efficiency associated with treating cattle for fluke at housing.
  • Cattle exposed to liver fluke infection should be dosed either at housing, or at a delayed interval post-housing as not all products are active against early immature fluke.
  • Dosing at housing will immediately remove the impact of developing and adult flukes on growth and feed efficiency. However, were this approach is practiced, cattle should be tested later in the housing period for the presence of adult fluke, or given a second treatment to ensure all fluke are removed.
  • Alternatively, if using products containing closantel or nitroxynil then consider delaying treatment for 6-7 weeks; with oxyclozanide or albendazole delay 10-12 weeks, as the majority of fluke will then be susceptible to treatment.
  • Very few products can be used in dairy cattle, and veterinary advice should be sort for treatments at drying off and only considered if there is evidence of fluke infection in the herd.
  • Only products containing oxyclozanide or albendazole can be used in lactating cows, providing milk withholding periods are observed, so it is important to check labelling on individual products
  • A bulk milk tank ELISA to monitor herd exposure to fluke and efficacy of control programmes is available.
  • For more information consult the COWS website (

17-10 PF F5

Pour-on preparations of 3-ML wormers, are also effective in controlling both sucking and chewing lice.

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


Worming ewes at lambing time

· With lambing now well under way, attention should be focusing on controlling parasite burdens in ewes.

· The principle aim of worming ewes is to minimise the future contamination of pastures by worm egg output during the 'peri-parturient rise" (PPR).

· Eggs passed in the faeces of infected ewes hatch and develop into infective larvae, which can cause disease in lambs later in the season.

· Worm faecal egg output is much reduced in well fed ewes in good condition.

· Provision of 'safe grazing' for ewes and lambs available at turnout will also help avoid the risk of worm infections in lambs later in the season.

o 'Safe' pastures should not have been grazed by lambs the previous year and include fields grazed by cattle last year; and re-seeded pastures.

· If only limited safe grazing is available, then this should be reserved for ewes with twin lambs whilst those with single lambs can graze the more contaminated pastures.

· As wormer resistance is becoming more common, advice on worming ewes is changing, influencing both the choice and frequency of treatment post-lambing.

· The timing and choice of wormer are both important in controlling the PPR, as the ewes can quickly become re-infected, particularly when grazing heavily infected pastures post turnout.

· Current worming advice recommends leaving a proportion of the ewes untreated by targeting treatments to include;

o Gimmers and young ewes

o Ewes nursing twins and triplets

o Ewes in low body condition

· Ewes with single lambs or those in good body condition can be left undosed unless there is a risk from fluke or haemonchosis.

· Persistent, or long-acting wormers, which provide a prolonged period of protection if given later in the lactation period before ewes become re-infected from the in refugia population can be highly selective for resistance.

· Worms in refugia include the population of worms present in untreated sheep and the free-living population of eggs and larvae not exposed to wormers.

· The recommendation for long-acting formulations of moxidectin, is to use these products prior to lambing, or at turnout.

Further details can be found on the SCOPS website at

Ewe worming treatments should aim to reduce pasture contamination during the periparturient rise whilst at the same time not selecting for anthelmintic-resistant strains of parasites.

Some ewes nursing singles could be left untreated; seek veterinary advice for your farm.


· Severe outbreaks of nematodirosis can occur in 6 to 12-week-old lambs usually from April to June in some years, depending on prevailing weather conditions.

· Cold late springs followed by sudden changes in temperature can trigger a mass synchronised hatch of infective larvae leading to severe production losses and even death in lambs grazing contaminated pastures.

· Monitor the SCOPS website ( for regular updates on risk of disease in your area.

· As weather conditions during March and April can significantly alter early season predictions of nematodirosis for flocks lambing during March/April, an updated disease risk will be included in the NADIS May parasite forecast.

Nematodirus control

· Control is best achieved by grazing lambs on pasture not grazed by lambs the previous year ('safe pasture').

· Where this is not possible, and local weather conditions are such that an early hatch occurs, then late January/February-born lambs may need prophylactic anthelmintic drenching before the end of March. Consult the SCOPS website regularly for disease risk in your area.

· Late March/April-born lambs may require prophylactic anthelmintic drenching in May if prolonged cold weather during April delays hatching.

· While incidents of wormer resistance have been reported with Nematodirus, white drench (1-BZ) wormers are still generally recommended to control this parasite.

· As disease is primarily caused by developing larvae, faecal egg count (FEC) monitoring is unreliable in determining risk and the need to treat.

· When a white drench (1-BZ) wormer is used in outbreaks of nematodirosis, the FEC of several lambs should be checked 10 days later for the presence of other worm species, which if present, would require treatment with a wormer from another group.


Nematodirus infection in lambs.  These lambs suffered a serious and costly check in growth rate.


· Outbreaks of coccidiosis may be encountered during April in lambs between 4-8 weeks of age, particularly in twin lambs grazing contaminated pastures.

· Coccidiosis is a disease of intensive husbandry with stress a major factor in triggering outbreaks of disease.

· Adverse weather conditions, poor colostrum supply, overcrowding, wet muddy paddocks previously grazed by sheep, and/or extended housing periods all predispose.

· Reduction of stocking densities, batch rearing of lambs, creep feeding and avoidance of heavily contaminated pastures/premises are measures that can be taken to reduce the risk of disease outbreaks.

· Disease prevention can also include strategic dosing lambs on contaminated pastures with diclazuril or toltrazuril at around 3-4 weeks of age, or administration of medicated creep feed containing decoquinate for 28 days.

Liver fluke

· Sheep on premises with known fluke populations, or in high risk areas, should already have been dosed in the autumn and early winter and may need to be dosed again this spring.

· Chronic liver fluke may still be encountered in sheep flocks and can be confirmed by checking for the presence of fluke eggs in faeces.

· On positive farms, the presence of fluke eggs in faecal samples reflects inadequate control of fasciolosis and control should be reviewed.

· Limiting pasture contamination with fluke eggs from patent infections will help reduce subsequent fluke challenge later in the year.

· Flukicides containing closantel, nitroxynil, oxyclozanide or albendazole (at the fluke dose rate), are all effective against adult flukes present during the spring and should be used to reduce reliance on triclabendazole.

· Sheep should always be moved to clean pastures after treatment; and supplementary feeding may be necessary to maintain condition.




· Housed, yearling cattle not dosed in the autumn, may be at risk from type II ostertagiosis towards the end of the housing period.

· Prevalence of clinical disease is usually comparatively low and only a proportion of animals in a group may be affected.


· The disease presents as intermittent diarrhoea with loss of appetite and rapid loss of body weight.

· Mortality in affected cattle can be high unless early treatment with a wormer effective against both arrested and developing larval stages is given.

PGE Control

· Decisions should have been made on the parasite control plan for the forthcoming grazing season.

· Prevention of PGE in growing cattle on a sustainable basis is best achieved by annual rotational grazing (cattle/sheep/crops) but this is not often possible on many farms.

· Parasite control plans based on anthelmintic use may be strategic (early season dosing) or "wait-see" (monitor/treat in the latter part of the grazing season).

· To be effective, strategic worm dosing needs to be initiated at, or around turnout, to limit pasture contamination up to mid-July by which time the over-wintered larval population should have declined to insignificant levels.

o Strategic treatments include administration of a bolus at turnout. or administration of pour-on, or injectable macrocyclic lactones (MLs) at defined intervals.

· Cattle treated strategically should remain set-stocked, or moved to safe pastures (aftermaths) when these become available.

· If "wait and see", then ensure that effective, regular monitoring and diagnostic procedures are in place to act quickly if required.

· Where lungworm is a problem, there is still time to discuss control, including vaccination, with your veterinary surgeon before turnout in most areas.

· Vaccination of calves over two months-old requires two doses of lungworm vaccine four weeks apart with a second dose at least two weeks before turnout.

· For more information see the COWS ( website.


Unless safe grazing is available, dairy calves and suckled calves born during the previous autumn require preventive treatment in their first full grazing season to control PGE

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