The combination of warmer weather, rainfall and flood events present perfect conditions for the Australian sheep blowfly (Lucilia cuprina), which initiates more than 90 per cent of all flystrike in sheep.
The risk of flystrike increases once the temperature is above 17°C, wind speeds are moderate (<30 km/hour) and the fleece remains moist from rainfall for a few days.
Management of flystrike risks
To mature and survive, the blowfly feeds off protein, such as manure, urine stained wool and carcasses. Managing situations that provide these things will therefore reduce the risk of strike.
Preventative actions include:
- Regular inspections of all sheep mobs – at least every two days if preventative chemical has not been applied. If a long-active preventative has been applied, inspections can be less frequent but are still needed in case chemical missed areas or if rain has rinsed the chemical out of the fleece.
- Timing crutching and shearing so that animals have shorter wool during late spring and early autumn
- Disposing of struck wool appropriately; this helps reduce fly numbers
- Removing any dead carcasses lying in paddocks
- Minimising scouring by avoiding sudden feed changes, controlling worms and providing animals with access to clean water.
- Feeding good quality hay when pastures are lush which can help to bind faecal material reducing dags and flystrike
- Ensure docked tails cover the entire vulva (usually the third palpable joint). Mulesed animals can become flystruck when tails have been docked too short; this length allows urine to stream away from the breech, allows the swishing away flies away and reduces the risk of skin cancers
- Moving susceptible stock to low risk paddocks (if possible) such as those with higher ground, more breeze and are more open (scrub reduces wind and increases humidity)
Note: Setting flytraps will reduce the number of flies around your house, but the Australian Sheep CRC has found them ineffective in controlling sheep blowfly.
Flystrike treatment
Apply chemical according to label directions, and be aware of withholding periods – particularly the Wool Harvest Interval, the Export Slaughter Interval and Meat Withholding Periods – a must to protect the health of you, your staff and your export markets.
Treating struck sheep is vital. To treat effectively:
- Look for sheep that are lagging behind the flock and, if standing at ease, show irritation to some part of their body, such as trying to nibble at a particular part of their body or feet.
- Remove struck sheep from the mob. Clip affected region to both the struck portion and where the exudate stain has run or spread.
- Ensure a clean margin of two to three centimetres around the area is left; even more if long fleeces are likely to hang over the area when the sheep is standing.
- Dress clipped area with a chemical registered for the treatment of flystrike and reapply according to directions on the label.
- Place fleece removed from the struck area into a black plastic bag and leave in the sun; the heat generated inside the bag will kill the fly maggots.
- Consider culling sheep that have been struck this year as part of your strategy to produce a more flystrike resistant flock.
Sourced from Agriculture Victoria.
Visit the Sheep CRC website Fly Boss for flystrike biology, breeding resistance, management and treatment information, as well as decision support tools.
