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Beyond the Bale : September 2010
23 September 2010 BEYOND THE BALE FAST FACTS l It is important to have an integrated flystrike prevention strategy. l Early season insecticide treatment could effectively control breech strike in unmulesed sheep. l Other strategies to consider are crutching, clips and genetic selection. Interim results from a three-year, AWI- funded study show that early-season preventative insecticide treatment, applied in September or October, can effectively control breech strike in unmulesed sheep for six months in south-eastern Australia. This should be integrated with management strategies, such as crutching and shearing, and genetic selection to prevent the build up of excessive dags. The study, run by the Mackinnon Project at the University of Melbourne's Faculty of Veterinary Science, is also comparing the prevalence of breech strike in clipped and mulesed sheep. These sheep are only treated when more than two per cent breech strike occurs in a week. This compares the protection from breech strike in clipped sheep with the current 'gold standard' for control, namely mulesed sheep. A total of 3600 sheep are involved in the trial on three commercial farms, two in the Western District, at Coleraine and Ballarat, and one in East Gippsland. Sheep in all groups are being compared for traits that indicate susceptibility to breech strike, such as breech wrinkle, dags and stain. As the trial progresses, the costs and returns on the three groups -- unmulesed, mulesed and clipped -- will also be compared. The study has found that most breech strikes have been related to dag and breech wrinkle. This is a similar finding to other large scale projects funded by AWI, studying the role of genetic selection for a range of breech traits in reducing the occurrence of breech strike. Dr John Larsen, who is overseeing the Victorian project, says early season treatment of over 1200 unmulesed sheep with dicyclanil (ClikTM) prevented all but four breech strikes, with all of these occurring on the one farm (1.7 per cent WOOL PRODUCTION of the unmulesed sheep on this farm). On another farm, treatment was fully effective even when applied over dags. However, on the farm with some breech strikes there was an indication of a reduced period of protection if sheep developed dags or heavy stain after the application of the ClikTM, but this needs to be tested further. "The trial has shown that early application of dicyclanil effectively prevented breech strike in the unmulesed sheep. Reducing dag by selecting rams that don't scour, so their progeny have less dag, and altering the timing of crutching of unmulesed sheep, are other critical areas which can help control breech strike in unmulesed sheep," Dr Larsen says. In 'daggy' environments, such as Gippsland and Western Victoria, an additional crutching of unmulesed sheep might be needed. Some modification of shearing gear may also be necessary, as using wide combs on very daggy sheep did result in more breech cuts on the unmulesed sheep. The use of clips did provide some welfare and management advantages, such as having less dag and not taking as long to crutch as the unmulesed sheep. However, there were from two to 12 per cent breech strikes in clipped sheep, compared to zero to three per cent in the mulesed group. This means that clipped sheep should always receive preventative treatments in areas that have a high risk of breech strike. "While cost comparisons still need to be worked out and will change by the end of the three years, our preliminary estimate is that it will cost an additional $1.80 to $2.40 per head per year extra to run unmulesed sheep. Additional crutching and insecticide treatments are a major component of that cost, but will vary considerably between farms," Dr Larsen says. Factoring in additional management costs will also be needed. For example, unmulesed ewe hoggets took from 23 to 52 seconds (90 to 145 per cent) longer to crutch than mulesed ewe hoggets and carried 270 grams (180 per cent) extra dags. The Clipped ewe hoggets were intermediate, taking 13 to 21 seconds (40 to 80 per cent) longer to crutch than mulesed sheep with 180g (120 per cent) extra dags. "In the short to medium term, growers are going to have to manage unmulesed sheep quite differently. This will include not letting them get excessive dags, as the penalties for increased crutching times are magnified in these really daggy sheep," Dr Larsen says. "Good worm control is already essential in these high rainfall environments, but it will become more critical with unmulesed sheep." More information: www.wool.com/flystrike www.mackinnonproject.com.au Integrated management a key defence