Dr Belinda Edmonstone, Forbes District Veterinarian
Over the past month, increased storm and rain activity in parts of the region has increased the risk of fly strike, making now a good time to review the blow fly story.
The three determining factors for fly strike are:
- Suitable weather conditions. Warmth and moisture favour blowfly activity and also contribute to the development of predisposing conditions on the sheep.
- Susceptible sheep. Wrinkly skin and dags are the most important determinants of breech shrike. Others include cover on the breech, yellow wool and urine staining. Fleece rot predisposes to body strike as does lumpy wool, body wrinkle, wool colour and structural conformation. Flies are also attracted to any injury or wounds such as marking/mulesing wounds, poll damage on rams and foot abscess/footrot.
- Flies ready to lay eggs on the sheep. Lucilia cuprina is the blow fly responsible for 90% of fly strike in sheep. The blow fly survives winter when maggots from the previous autumn overwinter in the ground as larvae. When the soil temperature increases to greater than 15°C the larvae pupate and emerge. A fly can lay up to 300 eggs in a cycle with egg laying occurring every 4 to 8 days. The eggs hatch within 24 hours and the maggot immediately starts feeding on the sheep. The life cycle is 2.5 to 3 weeks.
Crutching and mulesing are important tools in the management of breech strike as is shearing. Shearing is also an important tool for the management of body strike. In addition to this there are some very handy chemicals available making the management of fly strike simpler.
Your choice of chemical will be determined by method of application, how long it will provide protection, whether or not a lice treatment is also required and the withholding periods (including wool harvesting interval, export slaughter interval and meat withholding period).
Chemicals should be used strategically in combination with breeding, shearing and crutching.
Australia Wool Innovation has developed a handy web site to help you manage flies in your flock – check out www.paraboss.org.au. This allows you to develop an annual fly management plan for each class of sheep and to compare different plans to determine which one gives the lowest risk profile in the fight against flies.
Alternatively, give one of the District vets a call at Central West Local Land Services on 1300 795 299.