Any open wound is susceptible to flystrike. Female blowflies are attracted to these wounds where they lay eggs. These eggs hatch within a few hours and the maggots burrow into the wound and feed. These maggots feed for four to five days, increasing the wound size and attracting more blowflies to lay eggs.
The incidence of flystrike in cattle in Australia is low, but does occasionally occur in wounds through normal management operations such as castration and dehorning. The navels of newborn calves and any large wound can also occasionally be a target for blowflies. Similar to sheep flystrike, long-haired cattle breeds such as Scottish Highland Cattle may be susceptible to flystrike if the hair is heavily contaminated with faeces and urine.
To minimise injury to other cattle all horned cattle should be dehorned as young as possible. Where possible dehorn and castrate cattle during cool weather, or at least during the cooler parts of the day, and avoid humid or rainy weather. If blowflies are visible when performing these operations, an insecticide can be applied around the wound – do not apply an insecticide straight on the wound.
Inspect regularly up to about 10 days after treatment so that any infection or flystrike can be detected and treated early.
Screw-worm flies are found in Papua New Guinea and Indonesia but are currently not present in Australia. These flies are considered the most serious exotic pest threatening Australia´s livestock industries.
Screw-worm flies look very similar to other shiny blue-green blowflies found in Australia. The difference between these flies and other blowflies is screw-worm fly maggots only grow in living flesh. These flies are much more likely to be attracted to any wound including those from normal management operations such as castration, dehorning, and ear tagging, as well as from dog bites, cuts, scratches and lesions caused by ticks and buffalo flies. The navels of newborn calves and the vulval area of cows after birthing are very susceptible to screw-worm attack.
Screw-worm maggots are hard to see as they often burrow deep into wounds (Figure 1 and Figure 2) and will often weep and emit a pungent, rotten smell.
Figure 1. Screw-worm fly maggots have burrowed deep into a leg wound. Image courtesy of Rudolf Urech, Queensland Department of Agriculture and Fisheries
Screw-worm is a notifiable disease and any wound with maggots in it must be reported to the Emergency Animal Disease Watch Hotline on 1800 675 888.
Figure 2. Screw-worm fly maggots in a wound. Image courtesy of April Wardhana, Queensland Department of Agriculture and Fisheries