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Beyond the Bale : September 2014
42 ON FARM AWI supports genetic research to identify sheep with high natural resistance to breech strike. Breeding naturally resistant sheep is a long term, sustainable solution to reducing the risk of breech strike in Australian sheep. Two self-replacing breeding flocks at Mt Barker in WA (medium wool, Mediterranean environment) and Armidale in NSW (fine/ superfine wool, high summer rainfall) indicate that different factors, in different environments have differing effects on the level of breech strike resistance in sheep. Tony Schlink of DAFWA and Jen Smith of CSIRO presented the latest research findings from these two sites at last month’s National R&D Technical Update on Breech Flystrike Prevention. The key conclusion from research at both sites is that large differences exist between sire progeny groups, and some sires’ progeny are naturally very resistant to breech strike. Breech strike is heritable; therefore cull struck sheep. At Armidale, where breech wrinkle and cover are high, those traits are the major cause of breech strike. Few animals in that environment become daggy, but those that are more wrinkly and have greater breech cover are more prone to dag and urine stain. Any animals that do become daggy or highly urine stained during the fly season are at very high risk of flystrike. At Mt Barker, the sheep are low in wrinkle and breech cover, but because they are in a high dag environment during winter and spring, overwhelmingly dags and urine stain are the major causes of breech strike. Results at both sites show that when breech wrinkle is score 2 and less, dags score 2 and less and breech cover score 3 and less, the risk of breech strike is minimised. If sheep are at this target, either through breeding, some form of breech modification, or both, then the risk of breech strike in normal challenge conditions is low. The rate of progress in improving breech strike resistance through breeding varies with sheep type, environment and production system. Relatively quick progress in breeding terms can be made to reduce wrinkle – perhaps 10 years to reduce the flock average wrinkle by one score. It takes longer to breed lower breech cover, depending upon the type of sheep. Reducing dags is more difficult in high dag country where the environmental causes of dags can slow genetic progress where selection for dag reduction is also required. Another research finding was that low wrinkle and low breech cover sheep demonstrate better reproduction qualities. A key message for commercial woolgrowers is that the ram breeding industry is now breeding new lines of low wrinkle, low breech cover as well as low worm egg count sheep with relatively high fleece weight. Researchers at Mt Barker found that some plain-bodied sheep or low dag sheep can be more susceptible to breech strike than “normal” Merinos. Therefore, breeding plain-bodied sheep or low dag sheep will not necessarily solve all breech strike problems. The five known indicator traits (dags, stain, wrinkle, cover and colour) and the interactions between them explain 55 per cent of breech strike. Ongoing research is trying to find the cause of the yet unexplained 45 per cent. Wax, suint, dust and moisture have little impact. Skin with wool sample comparisons between the resistant and susceptible bred lines are showing that the resistant sheep have a much wider variety and much higher populations of bacteria. This is being validated on more Mt Barker sheep, after which the Armidale sheep will be sampled. It appears that odour emitted from sheep plays an important role in attracting or repelling blowflies. Work with detector dogs trained by Hanrob International Dog Academy in Sydney, has clearly shown that dogs can differentiate between non-fly struck wool from resistant and susceptible animals. AWI is currently funding an in-depth investigation into the bacteria species and populations found on resistant and susceptible bred lines of sheep. The bacteria/odour project is only in its initial stage but encouraging results have been found which support the outcomes found in the sniffer dog scoping trial and may take some pressure off the need for low dag, urine stain, wrinkle and cover. FOR BREECH STRIKE RESISTANCE BREEDING • Outcomes from the Breeding for Breech Strike Resistance Trial show that breeding can be an increasingly important option in the basket of tools for woolgrowers to reduce the risk of breech strike, particularly in low dag environments. • In high dag environments, crutching and the use of prevention chemicals will continue to play important roles, as dags can swamp both mulesing and low wrinkle/low breech cover genetics. • Selecting the best animals for your breeding flock requires the selection of both superior rams and ewes using traits that are easily and accurately measured, and that are heritable. • Sheep type, climatic variation between regions and between years strongly influences the risk of flystrike. MORE INFORMATION www.wool.com/flystrikeRnDupdate SHEEP FROM THE BREECH FLYSTRIKE RESISTANT LINE AT THE CSIRO’S ARMIDALE RESEARCH SITE SHEEP FROM THE BREECH FLYSTRIKE SUSCEPTIBLE LINE AT THE CSIRO’S ARMIDALE RESEARCH SITE.