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Beyond the Bale : Jun 07 - Jul 07
By Dr Gio Braidotti Today there are about 95 million sheep in Australia, but one ram alone stood out so much from the flock that his death early this year was chronicled in newspapers across the country. His name was Cojak and he became the reason for a nationwide search for other sheep that bore his trademark trait -- a bare backside. It was a mutation, a beautiful mutation, because it precisely mimicked the desired effect of mulesing and crutching. It was breeders Niel and Pat Smith who in 2002 spotted the significance of their bare-breeched ram, born on 'Calcookara', near Cowell in South Australia. The Smiths reported Cojak to researchers at the Roseworthy Campus of the University of Adelaide, who remember receiving the call. "We raced out to the property to take a look," Professor Phil Hynd says. "It was an exciting find and it kicked off an AWI-supported program to unravel the underlying genetics." Within 12 months -- the same amount of time it took the ram to produce a 14-kilogram, 21.4 micron fleece -- Professor Hynd's team also confirmed the Smiths' suspicion: the ram was passing the trait to his offspring. "We tested the progeny and found the trait is as heritable as common wool traits that breeders routinely select for," he says. "That makes Cojak the first sheep to indicate that a genetic solution to blowfly strike is possible, and this is a major contribution." As woolgrowers and stud breeders across Australia were put on alert, more bare-breeched rams were found; enough for a five-year breeding trial by CSIRO and the Department of Agriculture and Food, Western Australia. This study seeks to estimate how long it takes to breed for breech-strike resistance and also determine the trade-offs that may occur with other commercial characteristics, such as fleece weight. Cojak's legacy is also being felt at AWI's Falkiner Memorial Field Station, which is taking part in the biggest sheep gene-mapping project in the world. Dr Troy Fischer, AWI program manager for sheep productivity, is using the facility to identify DNA markers for the bare-breech trait. Even more strikingly, a large commercial flock of 25,000 sheep in WA was recently identified as having hundreds of bare-breech animals. Even though he is in a 500-millimetre rainfall zone, the WA breeder says he has no flies, no 'dermo' (dermatophilosis, or fleece rot) and is marking greater than 100 per cent lambs. When pedigrees were checked, it was discovered that the WA flock is based on similar bloodlines to 'Calcookara'. "Given all the scientific work being done on Cojak's bare-breeched brethren, we can say the sire lives on," Professor Hynd says. "Despite his death, he is still helping to transform how we go about defending Australia's flocks against blowfly strike." ú More information: Dr Troy Fischer, 02 8295 3151 Vale to a bare-breech trailblazer A ram whose genes could mimic the effects of mulesing and crutching has died, leaving science a mighty genetic legacy and a major challenge. Bare-breech rams opening frontiers The search for alternatives to mulesing is seeing the progeny of bare-breech rams take part in two large- scale studies designed to understand the heritability of the trait and its effect on other production traits, and to map the trait to discrete regions of the genome in the world's largest sheep gene-mapping project. On the genome front, Cojak was one of 20 rams being used to generate 5000 DNA-tested progeny in a bid to develop molecular markers that could fast-track future selection-breeding efforts. In addition, more than 100 other traits are being measured in a project that could go a long way to explaining variation among lambs for commercially important traits.The second project involves bare-breech rams that have been selected from different environments right across Australia.The five-year breeding trial will see each animal scored for bareness and wrinkle and joined to normal and bare-breeched ewes. The progeny will be tested for breech-strike resistance. In all, 600 ewes are involved at each of two sites: one in NSW, the other in WA.Throughout, each animal is being measured for production traits and monitored for flystrike. By the end of the trial, scientists hope to have a far better understanding of various breech traits and their heritability, their effect on lifetime production, and any potential management benefits of bare-breeched sheep. 17 GENETICS BEYOND THE BALE The inherent worm resistance of Merinos In subtropical areas such as India and Indonesia, where livestock can become burdened with enormous worm loads, natural selection has seen the emergence of sheep breeds with exceptional worm resistance. However, these breeds lack the valuable wool and production traits of Merinos. Australian geneticists have proved that Merinos can retain their productivity while achieving an equivalent level of worm resistance to their Asian counterparts. The proof is in selection lines established 20 years ago in each of Australia's different climate zones. A good example is the Rylington Merino line, founded by Dr John Karlsson of the Department of Agriculture and Food,Western Australia. In 2007, the line celebrates its 20-year anniversary as one of the most worm-resistant Merino flocks in Australia, while substantially improving production characteristics over the past two decades. "We have found that the animals have cross- resistance to the major parasites, including barber's pole worm, that cost the industry $400 million a year," Dr Karlsson says. "However, the resistance does not seem to involve one or two genes of major effect, so molecular markers won't provide a quick fix but a useful adjunct for breeding. Currently, selection is based on faecal egg counts (FEC), using test regimes suitable for different climate zones." With Sheep Genetics Australia already incorporating the FEC test into its Australian Sheep Breeding Values (ASBVs), Dr Karlsson emphatically believes that ram breeders can make substantial genetic gain by exploiting the genetic resistance inherent to Merinos. Indeed, he has already done so on his own 2000 head of sheep. He started in the 1980s, when he sensed that chemical drenches and mulesing were in for long-term problems. "On the back of that breeding, I stopped mulesing in 2000 and I have nearly phased out drenches," Dr Karlsson says. He is adamant that there are whole-farm benefits to breeding for worm resistance and other 'easy-care' traits. ú More information: Dr John Karlsson, firstname.lastname@example.org "On the back of that breeding, I stopped mulesing in 2000 and I have nearly phased out drenches." -- DR JOHN KARLSSON Cojak's beautiful mutation: his legacy lives on.
Jun 07 - Jul 07 Supplement
Apr 07 - May 07