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EXTERNAL PARAS I TES
WORKING
TOGETHER
FOR A HEALTHIER FUTURE...
9
LIVESTOCK MATTERS
Veterinary surgeon
Rod Welford
XLVets practice
Millcroft Veterinary
Group
ROD WELFORD,
MILLCROFT VETERINARY GROUP
Exploring the external
parasites in
sheep
The significant external parasites in sheep in the UK, often termed ecto-parasites
comprise lice, blowfly, headfly, ticks and sheep scab. Knowing the parasites in your
flock not only ensures that the correct treatments can be used, but also allows you
and your vet to put suitable control programmes, along with biosecurity measures
in place to minimise the welfare and economic concerns these parasites cause.
Here’s a guide to what’s out there and the treatment options available.
Fly control
l
Regular application of synthetic
pyrethroid (SP) pour-on during high
risk periods is the treatment of choice
for headfly.
l
Plunge dipping in SP or organophosphate
(OP) dip can provide protection against
blowfly strike for 3-8 weeks.
l
Application of SP pour-on should provide
protection against blowfly strike for 6-10
weeks, depending on the product used.
l
The insect growth regulator pour-ons
cyromazine and dicyclanil provide
protection against blowfly strike for 10
and 16 weeks respectively.
l
Implementation of gut worm control
strategies in accordance with SCOPS
principles
1
should reduce faecal
contamination of the fleece, and thus
incidence of blowfly strike.
l
Environmental control of flies, particularly
around farmyard areas can also
be tackled.
l
Regular dagging or crutching of sheep
remains an effective tool in further
reducing faecal contamination.
Blowfly strike
(maggots)
Blowfly strike is the infestation of living tissues
with the larvae of the flies Lucillia sericata
(greenbottle), Phormia terrae-novae (black
blowfly), or Calliphora erythrocephela
(bluebottle) and typically occurs from late
spring to early autumn in the UK.
Egg laying Lucillia or Phormia female flies
are attracted to fleece contaminated by
urine, faeces, decaying organic matter, or
excessive sweating. Hatching of larvae
occurs within 24 hours of egg deposition
under optimal conditions with the subsequent
invasion and digestion of the underlying
tissues. The wool in such areas takes on a
brown appearance, and the resultant
characteristic foul smell attracts a secondary
wave of blowflies, which may then include
Calliphora flies.
Untreated sheep die an unpleasant death,
usually due to toxaemia as a result of
absorption of toxic breakdown products in
conjunction with secondary bacterial infection.
Headfly
The headfly Hydrotea irritans can present a
significant challenge to sheep at pasture
during the summer months. Often gathering
round the sheep’s head in large swarms, the
irritation produced by the feeding of adult flies
on nose and eye secretions, wounds, or at
the base of the horn in horned sheep, can
cause the sheep considerable annoyance and
distress. Head-shaking and ear-flicking are
often observed, while scratching with the hind
feet and head-rubbing further traumatise the
skin. This merely serves to attract more flies
and sometimes loss of large areas of skin from
the head results. Secondary infestation with
blowfly larvae may also arise.