C.A.H.L.
- YOUR PARTNER IN ANIMAL HEALTH
BLOWFLY
STRIKE IN SHEEP
Blowfly
strike (Myiasis) in sheep was the cause of untold misery and death in
sheep before the advent of dipping. Fly strike in sheep is predominantly
caused by the greenbottle (Lucilia sericata) which prefers to lay its
eggs on the living sheep. Fly strike may occur on any part of the body
where the fleece has become soiled or infected with bacteria (body strike).
Sheep are most commonly struck around the rear end where the wool becomes
soiled by faeces and urine (breech strike). Castration and tail wounds,
clipping wounds, head wounds on fighting rams and any open wound will
attract flies (wound strike), particularly if infected by bacteria.
The smell of footrot is particularly attractive to flies especially
blowflies and often the fleece over the chest wall becomes contaminated
from the infected foot when the sheep lies down. Fly eggs, once laid,
hatch within a few hours or days. The emerging larvae or maggots are
very active and secrete enzymes which liquefy the skin and flesh of
the sheep upon which they are feeding. Larvae feed for a variable time
period depending on the availability of food. The mature maggots crawl
off the fleece and pupate in the soil. In suitable weather conditions
in the summer it takes less than a week for the fly to emerge, but often
it is two or three weeks. With flies laying thousands of eggs, it is
easy to see why the population of blowflies increases so rapidly under
warm, thundery weather conditions.
SYMPTOMS
Sheep suffering from fly strike show obvious signs of distress. They
spend less time grazing and more time tail wagging and rubbing the affected
area and biting the struck areas of the fleece they can reach. If these
signs go unrecognised and secondary strike occurs, the wounds can become
very extensive and bacterial infection may lead to serious complications
such as death from speticaemia and toxaemia. On examination of the sheep
the result is often a foul smell from the wound and visible signs of
maggots.
TREATMENT
& PREVENTION
Treatment of blowfly strike should aim to kill any maggots present,
prevent the likelihood of further fly strike and assist the wound heal.
The wool should be carefully clipped away from around the wound and
surrounding area. A suitable insecticidal cream should be applied to
the infected areas. Mild cases should heal quickly with correct treatment.
Special attention should be paid to high risk sheep, such as those with
dirty rear ends particularly during the period of risk, from May to
September. If fly activity is likely to remain high, the flock should
be dipped. It is particularly important to immerse sheep for at least
a full minute so as to ensure the dip saturates the whole fleece and
regular replenishment of dip baths is important to maintain the strength
of dip concentrate. Dipping is effective against the sheep scab mite,
insect parasites and the blowfly. The pour-ons are effective against
blowfly strike. The withdrawal period following dipping can be 35 days
versus 3 days for pour-ons. Contact your CAHL representative for further
details.
