Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB
Parasite Forecast - April 2017
February started mild and unsettled becoming colder with some
snow in the second week. Mid-February onwards was mild turning wet
and windy from the third week with snow to parts of Scotland. The
UK mean monthly temperature was 5.3 °C; the ninth warmest February
since 1910. Mean maximum temperatures were 1.0 -1.5°C above
average, with mean minimum temperatures more than 2 °C above over
much of England and Wales, but nearer 1 °C above over much of
Scotland. Rainfall was mostly near. or above, normal except
in northern Scotland and parts of SW England.
Worming ewes at lambing
- 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
- Worm faecal egg output is much reduced in well fed ewes in good
- 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.
- Safe pastures should not have been
grazed by lambs the previous year
and include fields grazed by
cattle last year, and reseeded pastures.
- If only lmiited 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
- 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
- Current worming advice recommends leaving a proportion of the
ewes untreated by targeting treatments to include;
- Gimmers and young ewes
- Ewes nursing twins and
- 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
- 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 www.scops.org.uk.
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
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
- Monitor the SCOPS website (
www.scops.org.uk) for regular updates on risk of disease in
- 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.
- 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
- 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
- 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
- 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.
- 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
- On positive farms, the presence of fluke eggs in faecal samples
reflects inadequate control of fasciolosis and control should be
- Limiting pasture contamination with fluke eggs from patent
infections will help reduce subsequent fluke challenge later in the
- 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
- Housed, yearling cattle not dosed in the autumn, may be at risk
from type II ostertagiosis towards the end of the housing
- 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.
- 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.
- Strategic treatments include
administration of a bolus at turnout or
pour-on, or injectable macrocyclic lactones (MLs) at
- Cattle treated strategically should remain set-stocked, or
moved to safe pastures (aftermaths) when these become
- If "wait and see", then ensure that effective, regular
monitoring and diagnostic procedures are in place to act quickly if
- 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 (www.cattleparasites.org.uk)
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
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.
Enrol by clicking