Use of a threshold of flystrike risk as a method for treatment intervention in the management of flystrike in sheep

Cost is important when determining preventative treatment for flystrike. This paper presents modelled output comparing two common treatment alternatives; either a fixed annual application date or waiting until a set proportion of the flock is struck. The Inverell, Gunning and Flinders Island regions of Australia, which provide differing strike conditions, were used for analysis. Where the period of annual strike risk was longer than the period of protection provided by chemical treatment, it was economically favourable (by 1–3%) to wait until a pre-determined proportion of the flock were struck before applying preventive treatment, rather than always treating on a fixed date. However, with spring or autumn shearing, where the season of strike risk was a similar length to the protective period, it was preferable to treat on a fixed date. For Flinders Island, with a shorter flystrike season than Inverell or Gunning, there were small benefits in treating at a pre-determined threshold, but selection of the correct intervention point was critical. In areas with lower levels of risk, where treatment may not be required every year, it appeared beneficial to set a threshold at a sufficiently high level to eliminate most treatment intervention except for years with high rainfall and humidity.