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Beyond the Bale : Aug - Sep 08
10 Road to 2010 BeYond The Bale Trial results support genetic alternative to mulesing Results are starting to come through from trials evaluating the effects of not mulesing and the effectiveness of breeding for breech-strike resistance By Fiona Conroy E TraiT Greasy fleece weight (kg) Clean fleece weight (kg) Fibre diameter (micron) CV (%) staple strength (n/kt) staple length (mm) Yield (%) vidence from research trials in New South Wales and Western Australia shows that selective breeding has the potential to reduce the incidence of breech strike, but still has some way to go to replicate the benefits of mulesing. Breech wrinkle and dags are emerging as the key factors influencing breech strike in both trials, which are also showing a reduced risk of breech strike in plainer-bodied sheep. Trials by CSIRO Livestock Industries and the Department of Agriculture and Food, Western Australia (DAFWA) are evaluating the impact of not mulesing and Table 1 Wool cut results for 2005-drop ewes bought in for the specific lines in the WA trial seleCT CommerCial 3.02 a 2.18 a 17.3 3.11 a, b 2.20 a 17.1 19.0 a 24.9 a 71.9 a 81.1 a 19.7 b 22.4 b 71.1 b 80.1 a note: a or b indicates significant differences between the different lines ConTrol 3.17 b 2.27 b 17.0 19.6 b 23.3 a, b 71.8 a 79.0 b the effectiveness of breeding for breech-strike resistance using a number of indicator traits (including breech and crutch cover, body and breech wrinkle, dags, urine stain and wool traits). The research began in 2005 and involves a fine/superfine flock at CSIRO Armidale, NSW, which is run under high summer rainfall conditions, and a medium wool flock, which is run under winter rainfall conditions at Mount Barker, WA. Each site has a flock of 600 ewes run in three lines with varying selection pressure for breech-strike resistance. Mature ewes were sourced from research stations and ewe weaners were screened from participating wool producers’ flocks and brought in to fast-track the breeding program. Both sites have a group of 200 ewes run as an unselected control (UC), which is a randomly bred line representative of flocks in the district. A second group of 200 ewes is managed as a commercial improvement (CI) line to reflect what could be achieved in a commercial flock using a base of unselected ewes joined to sires selected for breech-strike-resistance characteristics. The third group of 200 ewes, known as the plain breech (PB), or selected, line, reflects a stud situation, and both ewes and rams are put under intense selection for breech strike resistance indicator traits while attempting to maintain current wool production. At each site ewes are joined annually to one of 12 sires Figure 1 2005 vs. 2006 drop results up to hogget shearing (WA) Sheep struck (%) 35 30 25 20 15 10 5 0 Plain breech (selected) (PB) 2005 mulesed 2005 unmulesed Commercial improvement (CI) 2006 mulesed 2006 unmulesed Unselected control (UC) by either artificial insemination or natural mating. Most sires have been sourced from the wool industry, but some are a result of breeding programs for superfine wool (CSIRO Armidale, NSW) and worm resistance and dags (Rylington Merino, Mount Barker WA). Two sires are annually used as link sires across the New England and WA sites. Half of each lamb drop in each of the three lines has been mulesed and half remain unmulesed. The sheep are not given a preventative fly control treatment. They are heavily supervised and once struck the sheep are quickly treated. Results to date show that the unmulesed sheep intensively selected for breech-strike- resistance characteristics are experiencing a lower rate of breech strike than the unmulesed CI and UC lines of sheep. Mulesed sheep in the selected lines are also experiencing lower rates of breech strike than the mulesed control lines of sheep. However, over both years, unmulesed selected lines are not close to having the same level of breech strike protection afforded to mulesed sheep, with mulesing reducing the incidence of breech strike by about 75 per cent. It is important to note that no fly preventative treatment is used in the trial. Figure 1 highlights the variability in flystrike between seasons and, as more years of data become available, a clearer picture will be presented. The research is also enabling development of preliminary estimates of heritabilities and correlations between indicator traits and breech-strike incidence, which can be incorporated into performance-recording systems such as MERINOSELECT. In addition, changes over time in breech characteristics of individual animals are being monitored in order to make recommendations regarding the ideal age to score sheep. Dr Jen Smith, breech strike genetics project leader for CSIRO Livestock Industries, says the most recent results from the research put the estimated heritability for breech wrinkle at 0.38. “This means it is moderately heritable and can therefore be changed through selective breeding,” Dr Smith says. “To make a comparison with other traits that woolgrowers are probably more familiar with, the heritability is similar to fleece weight. “It shows we can make changes using genetics, but it’s a gradual process. The really important thing about selective breeding is that any change you make is permanent and – if you maintain the same breeding objective – then the improvements are cumulative over successive generations. “In the Armidale flock to date, breech wrinkle and dags are more closely associated with breech strike than breech or crutch cover. “Merino breeders in this region have traditionally had a degree of wrinkle in their Merinos, as well as wool coverage down the points, in the belief that it is important to maintain fleece weight. Naturally, they have concerns that breeding for the bare-breech characteristic will result in sheep with bare points and a much lower wool cut. “But shearing results from the trials show that well- covered, plain-bodied sheep with less breech wrinkle are still productive.” In WA, DAFWA senior geneticist Dr Johan Greeff and senior veterinarian John Karlsson say results at Mount Barker are also showing that breech wrinkle and dags are the main contributing factors for breech strike in unmulesed sheep. “People have tended to breed sheep with wrinkles in the belief that they are heavier wool cutters,” Dr Greeff says. “But research has shown that wrinkled sheep are more susceptible to flystrike, are generally smaller, less fertile, have a higher mortality rate, are less hardy and have more variable fleece quality. “Our shearing trials are showing that the plainer-bodied sheep in the intensely selected line have good clean fleece weights, with longer, stronger staples.” (See Table 1.) Dr Karlsson says sheep in winter-rainfall regions are also more prone to dags, which are a serious cause of breech strike. “Dags can undo all the best efforts to reduce breech strike through genetics, and even result in mulesed sheep getting struck.” More information:www.wool.com.au/2010; dr Jen smith, firstname.lastname@example.org; dr Johann Greeff, email@example.com ú
Jun - July 08
Oct - Nov 08