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Beyond the Bale : March 2015
42 ON FARM The Breech Strike Resistance Flocks at Armidale NSW (CSIRO) and Mount Barker WA (DAFWA) have shown that dags, breech wrinkle, urine stain, breech cover and wool colour all impact on the risk of breech strike, and the extent to which each trait leads to breech strike varies between regions and sheep types. Breeding values have been created for these traits and are available through MERINOSELECT. However it is clear from the information gathered from these flocks that there are other “as yet undetermined” factors influencing the risk of breech strike. In a scoping study, wool from unstruck sheep were used to train sniffer dogs to identify wool from resistant sheep while ignoring wool from susceptible sheep. The dogs showed that they could smell a difference and this led researchers to a new line of investigation, to find out whether resistant and susceptible sheep produce different odours that may be linked to different bacterial populations on their skin. The results from this work are exciting and could lead to a new breeding approach to breech strike, but the work has only been possible by having bred sufficiently divergent lines of susceptible and resistant sheep at both sites. In 2014 a PhD student Joe Steer at the University of Western Australia commenced work on trying to determine if and then what chemicals and odours were either attracting or repelling gravid flies (females looking to lay eggs). Three wool samples were taken in 2012, from the most resistant and the most susceptible 2008-drop sires at Mt Barker. The rams had BREECH FLYSTRIKE UPDATE BREECH ODOUR Wool samples from a susceptible sire and resistant sire in two separate glass flasks, with air blowing over them through to a Y-shaped glass apparatus towards a single opening (see below) Gravid flies (females looking to lay eggs) are released from the left. They head towards a Y-junction, at which point they choose either the direction of the resistant or susceptible wool. Significantly, all the flies tested have opted to walk in the direction of the susceptible wool. AWI-funded experiments undertaken at the University of Western Australia have shown that female blowflies looking to lay eggs are attracted by the odour of wool from flystrike susceptible sheep in preference to wool from flystrike resistant sheep, and work continues to isolate the specific ‘odour’ chemicals. The ultimate aim of the research is the development of a test that could be used on wool samples in a lab (like micron testing) to get a resistance/ susceptibility measure that will lead to reduced breech strike, reduced need for very low breech wrinkle and dags and reduced reliance on chemicals.