Flystrike is estimated to cost the New Zealand sheep industry about $37 million a year, with those losses coming from deaths, treatment costs, and loss of meat and wool production. Even relatively minor strikes can result in marked appetite loss and subsequent losses of weight with prolonged recovery times.
A simple plan for protection is to shear your sheep in late December and treat immediately or within a few days with spray-on or pour-on treatments like Clik (18 weeks protection), Zapp Encore (8 weeks). You may need to use a half dose as a crutch treatment at the end of this period to protect at the end of summer. Be sure to warn the shearer and discard this wool at shearing. Zapp Encore, Cyrex or Maggo can be used to treat fly blown sheep. Depending on the severity of the strike, sheep may need further treatment oreuthanasia. Talk to your vet. Below is a table of the products we recommend and stock at Cambridge Vets.
* at 3ltr applied wash
Four species of blowfly are recorded as causing strikes on sheep in New Zealand, with the Australian green blowfly [Lucilia cuprina] and the European green blowfly [Lucilia sericata] recognized as the most important primary strike flies.
Prevention of flystrike is largely reliant on the application of insecticides by a variety of means [saturation dipping, jetting, low volume pour-ons or spray-on] to the fleece of ‘at risk’ animals, along with good animal husbandry for effective worm control and to prevent faecal soiling, and crutching and shearing at appropriate times. The preventative chemicals most commonly used belong to the broad insect growth regulator [IGR] group of compounds.
The IGR’s fall into two distinct chemical classes;
1.Triazine/pyrimidine derivatives such as cyromazine [Vetrazin] and dicyclanil [CLiK and CLiKZiN]
2. Benzoyl phenyl urea [BPU] compounds represented by diflubenzuron and triflumuron
Lucilia spp blowflies have demonstrated a remarkable ability to develop resistance to various chemicals used to control or prevent flystrike, with resistance first manifested as a shorter than expected period of protection in spite of proper application and dosage. Strains of Lucilia spp. resistant to diazinon an organophoshate, have been recorded throughout New Zealand and recent surveys have suggested that there may be widespread resistance to BPUs in the Waikato.
Minimizing the losses caused by flystrike requires a planned preventative approach using effective products. A preventative approach means treatments are applied before expected fly activity rather than waiting until animals get struck. Resistance management needs to be factored in when planning flystrike prevention programmes, alongside other key factors such as rainfall, class of sheep, shearing, docking and weaning dates, product application method and previous fly challenge. If you have any doubts about the effectiveness of your current flystrike prevention programme please give us a call.
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