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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - June 2017

17-06 PF Capture

April started off warm followed by temperatures that were mostly close to average, with some cool nights, but ending with a late cold snap. Mean UK temperature was 8.0 °C, which is 0.6 °C above the long-term average.  Rainfall was below normal except in north-west Scotland and parts of SW England, with 48% of average overall, making it the 10th driest April since 1910.

June Parasite Forecast/Update



Parasitic Gastroenteritis (PGE)

  • Provision of "safe grazing" is a key component of the farm's sustainable parasite control programme and should be used to greatest benefit.
  • Lambs on "safe grazing" at the start of the grazing season (fields previously arable or grazed by cattle the previous year) shouldn't need worming until after they are weaned.
  • Ideally, wean the lambs onto silage or hay aftermaths that have not been grazed by sheep earlier in the year, as by mid-summer any over-wintering larvae will have died off and the fields can then be considered "safe".
  • Lambs grazing permanent pastures will usually require worming to limit the build-up of infective larvae later in the season ('mid-summer rise').
  • The timing of worming treatment(s) for lambs will depend upon grazing history, levels of contamination by periparturient ewes, stocking density, and prevailing weather conditions.
  • Performance monitoring, or worm faecal egg counts (FECs) of lambs every 2-4 weeks from June onwards, can be used to guide anthelmintic treatments.
  • Pooled faecal samples from approximately 10-12 lambs in a group will guide treatment.
  • Treatment is generally recommended when FECs exceed 500-700 epg.
  • Follow SCOPS recommendations by leaving some lambs untreated and monitor treatment efficacy by performing a drench test post-treatment (see below).
  • Prolonged local dry weather conditions during summer can delay larval challenge to lambs grazing contaminated pastures with a return to infectivity when wet weather arrives.
  • Remember to include rams in the farm's parasite control programme because they are fully susceptible to PGE.
  • It will take at least two months of good grazing for a ram to gain one unit of condition score with a target of 3.5 at mating in October/November.
  • Rams typically graze the same field every year with significant build-up of infection on this pasture.

17-06 PF1

Include rams in the farm's parasite control programme as they are fully susceptible to PGE; these rams need to start gaining condition before mating from September onwards.

17-06 PFF2

Planning ahead - silage aftermath should be grazed by weaned lambs as part of the sustainable parasite control programme on your farm

Targeted Selective Treatments (TSTs)

  • Some lambs in the flock in good body condition and performing well can be left unwormed.  In general, only 40-60 per cent of lambs require worming.
  • Target anthelmintic treatments for those lambs that are failing to meet expected growth rates by weighing lambs every 3-4 weeks.
  • Regular weighing also identifies poor growth which may be caused by overstocking, trace element deficiencies etc. and prompt management review.
  • Electronic identification and automated weight recording simplifies TST.
  • This strategy greatly reduces the likelihood of selecting for resistant strains of worms by allowing a pool of unselected parasites to pass out eggs onto the pasture helping to maintain wormer efficiency in the longer term.
  • Accurate record keeping also allows selection of the best genetics in the flock with breeding stock kept based on performance not appearance.

17-06 PFF3

TST selects only those lambs for treatment that are failing to meet expected growth rates.

Drench Testing

  • Testing for the presence of wormer resistance is an increasingly important part of maintaining an effective worm control strategy.
  • The cheapest and simplest way is to perform a drench test to check on anthelmintic efficacy.
  • Collect FECs, as previously described, both prior to worming, and again at either 7 days for 2-LV; or 14 days for 1-BZ and 3-ML wormers post-treatment.
  • If mean FECs have been reduced by <95% then resistance is suspected.

Fly Strike

  • Blowfly strike affects around 80% of UK sheep flocks each year.
  • Female flies are attracted by the odour of decomposing matter such as wounds or soiled fleece.
  • Shearing reduces the risk of blowfly strike in adult sheep.
  • Treat all shearing cuts immediately to prevent fly strike and further self-inflicted injury by the sheep.
  • Preventing diarrhoea caused by worm infections will greatly reduce the risk of blowfly strike on the breech.
  • Active maggot infestations can be treated using pour-on products containing (alpha) cypermethrin; spot-on products containing deltamethrin; or by dipping in diazinon dip baths.

17-06 PFF4

Treat all shearing cuts immediately to prevent fly strike and further self-inflicted injury by the sheep.


  • Strategic worm control in cattle is usually applied to autumn/winter-born weaned calves in their first grazing season, and in spring-born beef suckler calves in their second grazing season.
  • Wormers should always be administered following the COWS 5 R's principles - Right product; Right Animal; Right time; Right dose; given in the Right way (see for further details).
  • Cattle receiving strategic anthelmintic treatments in the early part of the grazing season must remain on the same pasture during the entire grazing season, or be moved to safe pastures (aftermaths) when these become available.
  • Strategic regimes based on products with prolonged persistence against the stomach worm, Ostertagia ostertagi, may allow the build-up of other worm species against which they have less efficacy, or little persistent effect (for example Cooperia species), which may appear later in the year.
  • Worm infections can reduce growth rate by around 30% in beef calves and replacement dairy heifers, even with low levels of worm challenge.
  • In dairy cows, worm infections can cause a drop in milk yield of 1 kg per day.
  • Incidents of clinical disease due to ostertagiosis in cattle peak during August/September.
  • In severe infections, there is ill-thrift, loss of body condition and diarrhoea.

17-06 PFF5

Strategic regimes are commonly used to control Ostertagia ostertagi infestation in autumn-born beef cattle during their second grazing season.


  • Lungworm disease ("Husk") appears from June onwards in unvaccinated calves, those cattle without an effective anthelmintic programme, and naïve adult cattle.
  • Early signs include coughing, initially after exercise then at rest, increased respiratory rate and difficulty in breathing.
  • Affected cattle rapidly lose weight and body condition and should be removed from infected pasture and treated as quickly as possible.
  • Supportive therapy may be required depending on clinical presentation.

17-06 PFF6


Severe lungworm infestation in a susceptible dairy cow from an organic farm where vaccination was not used.

17-06 PFF7

Large numbers of lungworms in the airways can result in severe respiratory distress and death.


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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