Spring is the best time in the Crookwell district to plan your fly strike prevention strategy. Fly strike is a painful and potentially life-threatening disease in sheep. It is a major cost to the sheep industry and causes significant loss of production each year – the development and implementation of a fly strike prevention strategy is an essential part of good sheep management.
Female blowflies (Lucilia cuprina) lay up to 3,000 eggs over 3 weeks. In ideal conditions – warm, humid and moist weather – L1 larvae hatch out in 12 hours. These first stage larvae cause no problems, but in 3 to 10 days they moult to second and third stage larvae, and it’s these that cause fly strike. The L3 larvae pupate in the soil and in 3 to 7 days develop into the adult fly.
It is desirable to select sheep with qualities less likely to predispose to fly strike. This means selection of sheep with fewer skin folds, especially around the anal and vulval areas. Some wool types are more vulnerable to fly strike, including wools with heavier yolk content.
Chemical prevention includes the topical use of insect growth regulators (IGRs). Crookwell Veterinary Hospital stocks two IGRs – Cyrofly 60 and Clik.
IGRs interfere in the sheep blowfly life cycle and are one of a number of chemical groups used to prevent blowfly strike.
Cyrofly 60 is a spray on that provides up to 11 weeks protection from blowfly strike on long wool sheep (including organophosphate resistant fly strains). Its active chemical cyromazine prevents fly strike by stopping the moulting of the benign L1 into the harmful L2 stage.
Cyrofly 60 is contraindicated for use on open wounds, including mulesing and marking, and its effectiveness is reduced in sheep with less than 6 weeks of wool.
Clik provides 16 to 24 weeks protection. A ready-to-use spray-on/pour-on formulation, Clik (dicyclanil) works in a similar way by preventing the moulting of treated larvae into the next larval stage. Clik is effective on all wool lengths, including off-shears, and is safe to use on mulesing and marking wounds.
Both products are preventative – that is, they should be used before an anticipated fly wave as the first stage larvae are the most susceptible and established strikes may not respond well to treatment.
When fly strike lesions are observed, it’s essential to immediately shear or clip excess wool from the area and apply appropriate chemical dressing to the wounds.
Chemicals that kill maggots effectively include diazinon and spinosad, applied as directed.
In severely affected sheep, long acting antibiotic injections are recommended to increase survival by controlling the concurrent bacterial infections and in some circumstances, pain relief may be indicated.