While sheep scab is the most important skin infestation, farmers
must also be aware of the other ectoparasite infestations that can
affect their sheep causing financial loss and welfare
concerns. Control of all ectoparasites infestations can be
achieved by strategic treatments and strict biosecurity although
these principles of disease control appear to have been largely
forgotten in the 20+ years since the cessation of compulsory plunge
dipping. Skin infestations in sheep are a major animal welfare
In the UK, headfly can present a major problem during the summer
months. Grazing patterns are disturbed and
affected sheep often isolate themselves and remain in shade where
available. They may stand with the head held lowered with
frequent head shaking and ear movements. Alternatively, sheep
adopt a submissive posture in sternal recumbency with the neck
extended and the head held on the ground. Kicking at the head
often greatly exacerbates damage caused by headflies and such
action may also traumatise the skin of the neck and ears. The
impact of headfly worry on sheep welfare must not be
underestimated. Fleece quality is adversely affected and the
loss of body condition sheep experience will reduce ovulation rate
in the autumn and subsequent litter size costing the farmer
Severe headfly lesion causing disrupted grazing and rapid
condition loss in this Texel cross lamb.
Abnormal behaviour shown by this Blackface ewe is caused by
headflies. Condition loss during the summer can cause poor
ovulation and reduced litter size at lambing time.
Topical emollients and antibiotic preparations are not usually
necessary and skin wounds heal well provided the flies are denied
access to these areas. Housing is essential for sheep with large
skin lesions to allow time for complete healing. Ear tagging
and notching must be undertaken carefully and not during the fly
Housing is essential for sheep with large skin lesions to allow
time for complete healing. Sheep must not be banished to hill
ground on the expectation that there will be no flies there.
Pour-on fly control preparations, such as high cis
cypermethrin or deltamethrin, must be applied before the
anticipated headfly season and especially to horned sheep with
re-application as directed by the manufacturer's instructions.
Cutaneous myiasis (Blowly strike,
Blowfly lesions may range from centimetre diameter areas of skin
hyperaemia with a small number of maggots to extensive areas of
traumatised/devitalised skin causing death of the sheep in
neglected cases. It is legal requirement to inspect all
lowground and upland sheep daily. Death of a sheep due to blowfly
strike could lead to prosecution under animal welfare
Adult flies are attracted to areas adjacent to faecal staining
surrounding the perineum.
Adults flies are attracted to areas adjacent to faecal staining
surrounding the perineum; and less commonly virulent footrot
lesions with exposed corium/exuberant granulation tissue,
dermatophilosis lesions on the skin, and urine scalding around the
prepuce. In severe infestations the sheep are depressed and
isolated from the flock. Large numbers of adult flies are
seen on the fleece with maggots on the blackened skin once the
surrounding fleece has been lifted clear. There is an
associated putrid smell.
Adult flies are
attracted to virulent footrot lesions.
Death caused by
extensive blowfly strike.
Affected sheep can be treated by plunge dipping using an
organophosphate preparation but it is more usual to treat
individual infested sheep with dip wash applied directly to the
struck area after first clipping away overlying wool.
Before preventive measures using various chemicals are
considered, much can be done to reduce the attraction of blowflies
for example a grazing programme to prevent the massive build up of
infective helminth larvae on permanent pasture during July and
August (mid-summer rise) reduces diarrhoea caused by high parasite
burdens. Where faecal staining of the perineum occurs this
wool must be removed ("dagging" or "crutching"). In adult sheep
removal of the fleece and any faecal contamination by shearing
during late May/June in the UK removes this attraction well before
the peak of the blowfly season.
staining of the perineum occurs this wool must be removed. What is
your opinion of the care of this sheep?
Dimpylate (diazinon) and propetamphos are effective against
blowfly strike for up to six weeks. These compounds are
strongly lipophilic and replenishment of dips is important to
maintain effective concentrations within the bath. It is
essential to follow all instructions on the data sheet.
While topical application of high cis cypermethrin
pour-on preparations provides protection against fly strike, these
preparations persist for only 6 to 8 weeks at the site of
application and require re-application in most situations.
The insect growth regulator, cyromazine, applied before the risk
period is effective against blowfly strike for up to 10 weeks after
topical application and dicyclanil affords 16 weeks' full body
application to the breech area.
rabbit shooting on this farm provides blowflies with the perfect
breeding ground to rapidly multiply and attack
Louse populations are highest during late winter in sheep in
poor body condition kept under unhygienic conditions rather than
the reverse situation where lice cause debility. The chewing
louse Bovicola ovis is the most common infestation and may
cause disrupted feeding patterns, fleece damage/loss, and
self-inflicted trauma. Spread occurs by close contact. The
slow reproductive capacity of Bovicola ovis results in a
gradual build-up of louse numbers over several months.
Louse populations are highest
during late winter and may cause disrupted feeding patterns, fleece
damage/loss, and self-inflicted trauma. Note also the faecal
staining on the tail of the ewe lamb on the left
Heavy louse infestation revealed in an emaciated ewe.
The important differential diagnosis for flock problems of
pruritus and fleece loss is psoroptic mange (sheep
scab). Reliance on systemic endectocides to control
sheep scab has resulted in an upsurge of louse infestations in
sheep flocks in the UK. Maintenance of a closed flock and
effective biosecurity measures would prevent introduction of louse
Lice or sheep
Louse infestation can be readily eliminated by plunge dipping
using an organophosphate preparation. Use of plunge dipping
for other reasons, such as control of sheep scab, cutaneous myiasis
and headfly problems, also effectively controls louse
infestations. Louse infestations can also be controlled with
topical application of high cis cypermethrin or
deltamethrin. The presence of lice on sheep reflects poorly
upon biosecurity measures and the overall flock health plan and
such infestation must prompt a review of these processes before
more serious and costly infections are introduced.
The presence of
lice on sheep reflects poorly upon biosecurity measures and the
overall flock health plan