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Beyond the Bale : September 2016
BREEDING FOR BREECH STRIKE RESISTANCE AWI has conducted 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, longer flystrike season) indicate that different factors, in different environments have differing effects on the level of breech strike resistance in sheep. Johan Greeff of DAFWA and Jen Smith of CSIRO presented the latest research findings from these two sites at the National R&D Technical Update on Breech Flystrike Prevention in July (see page 34). The key conclusion from research at both sites is that large differences in the incidence of breech strike exist between sire progeny groups, and some sires’ progeny are naturally very resistant to breech strike. ARMIDALE AND MT BARKER RESULTS 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 when they do the risk of strike is high. At Mt Barker, the sheep are low in wrinkle and breech cover, but because they are in a high dag environment during winter and Sheep from the breech flystrike resistant line at the CSIRO’s Armidale research site. KEY MESSAGES • Breeding is an important option in the basket of tools for woolgrowers to reduce the risk of breech strike, particularly in low dag environments, but there is no single simple ‘recipe’ for every woolgrower. • The rate of response will be different in every flock. Like any selective breeding, gains are cumulative and permanent. • Sheep/wool type, production system, environmental factors and climatic variation between regions and between years strongly influences the risk of flystrike. • 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. spring, the incidence of breech strike due to dags is higher. Results at both sites show that when breech wrinkle is score 2 or less, dags score 2 or less, urine stain score 2 or less, and breech cover score 3 or less, the risk of breech strike is minimised to a level similar to ‘mulesed’. If sheep are at this target, either through breeding, some form of breech modification, or both, then the risk of breech strike is low. As the breech trait scores are reduced further, the risk of breech strike continues to fall. The rate of progress in improving breech strike resistance through breeding varies with sheep type, environment and production system. Reducing wrinkle and breech cover is easier in medium wool type sheep and harder in fine and super fine type sheep as there are just fewer animals with low wrinkle and cover in these types. Reducing dags is very difficult in high dag country for all sheep types, where the environmental causes of dags swamp the slow genetic progress. A key message for commercial woolgrowers is that there are ram breeders, particularly with medium and fine wool type sheep, breeding sheep with significantly lower wrinkle, lower breech cover as well as lower worm egg count sheep with relatively high fleece weight. ODOUR AND SKIN BACTERIA While dags, urine stain, wrinkle and wool cover are key breech strike risk factors, researchers found some sheep that have high dag, stain, wrinkle and wool cover that do not get struck, and some sheep with low dag, stain, wrinkle and cover do get struck. 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 are important but do not explain all the causes of breech strike. It is suspected that the ‘as yet unknown’ risk factors are differences in odour and bacteria between sheep. Studies continue into determining what it is that is attracting female blowflies (Lucilia cuprina) to some sheep, and how and why its larvae parasitise some sheep and not others. A breakthrough in the odour and bacteria work is proving elusive despite considerable effort. Using gas chromatography technology the number of likely odour causing chemicals compounds are being identified. Then an electro-antennagram that measures the gravid fly’s response to each compound is used to narrow down the likely compounds that attract the flies. The goal is to be able to select and breed sheep that don’t emit the attractant odours along with the known key breech traits, and therefore reduce their exposure to and risk of breech strike. MORE INFORMATION The presentations of Johan Greeff of DAFWA and Jen Smith of CSIRO are available on the AWI website at www.wool.com/flystrikeRnDupdate 36 ON FARM
In the Shops - September 2016