Tools to reduce the risk of flystrike in sheep on your farm
Danny Roberts DPIRD, Albany WA and Johan Greeff DPIRD Perth, WA
Author correspondence: danny.roberts@dpird.wa.gov.au
September is normally the time when blowflies start to become a serious problem especially in long wool and uncrutched sheep.
Therefore, wool growers should monitor their flock closely and treat struck sheep immediately, by shearing the area around the strike site and treating it with an effective treatment.
Adult sheep blowflies do not travel very far from where they hatch and the risk of flystrike depends on the prevailing environmental conditions. Wet sheep and daytime temperatures higher than 15 degrees can result in both body and breech strike.
The most susceptible sheep are wrinkled and/or with dags. As dags are usually caused by worms, an effective worm management program is critically important during these times.
Sheep should be crutched to reduce the risk of flystrike in the coming months. A pre-shearing crutch can give up to six weeks protection from breech strike but is reduced to three weeks if your sheep are scouring.
Jetting and spray-on chemicals can be used as a preventative treatment to reduce the risk of flystrike but the decision needs to consider the increased risk of flystrike during this time of the year, how long before the sheep will be shorn and which chemical should be used. Rotate using different chemical groups to prevent flies becoming resistant.
Delays in shearing during spring often occur after prolonged wet weather. The risk of flystrike may be further complicated by any delays to shearing during spring. Consequently, knowing the wool withholding period (time between application of the chemical and when wool is harvested) is important consideration when choosing a chemical. Similarly, the export slaughter interval is of concern in treated sheep being sold.
Wool producers should visit DPIRD website (agric.wa.gov.au/livestock-parasites/flystrike-management-tools) to get important information on how to choose a suitable chemical to apply, access all the withholding requirements details, protection period for the different chemicals, and how to prepare a flock treatment timeline.
FlyBoss (flyboss.com.au/sheep-goats/treatment.php) also has several tools available to assist wool producers assess the risk of flies. The tools take into consideration whether sheep have been jetted, crutched, mulesed and how daggy and wrinkled the sheep are. The program will predict the risk of flystrike using real weather prediction data within 5kms of their chosen location.
Breeding for breech strike resistance offers the best long-term permanent solution. Struck sheep should be culled as breech strike is quite a repeatable trait. Sheep struck at a young age are most likely to get struck as older sheep.
To reduce a flock’s susceptibility to flystrike, wool producers need to breed more flystrike resistant sheep. Visit the Merinoselect website (sheepgenetics.org.au) to learn how to use Australian Sheep Breeding Values (ASBVs) to determine which ram is right for your flock.