HOW TO USE THIS ONLINE MAGAZINE
by clicking the arrows at the side of the page.
by clicking anywhere on the page. A slider will appear, allowing you to adjust your zoom level.
and move the page around when zoomed in by dragging the page.
and return to the original size by clicking on the page again.
by entering text in the search field and click on "In This Issue" or "All Issues" to search the current issue or the archive of back issues
a PDF of this magazine.
by clicking on thumbnails to select pages, and then press the print button.
a page via email, Facebook, Twitter and more.
TO VIEW PREVIOUS EDITIONS
, click the
button at the bottom of the screen.
Beyond the Bale : Jun - Jul 08 Supplement
By Kellie Penfold W hile there is no ‘silver bullet’ solution to aid woolgrowers in the phasing out of mulesing, genetics offer a path to breeding a more flystrike-resistant sheep.However, it is not a simple solution and growers are advised not to chase just one single trait – bare breech, for example. Early research data coming through the breech strike genetics program – a collaborative research effort of CSIRO Livestock Industries at Armidale, NSW, and the Department of Agriculture and Food, Western Australia, and funded by AWI – is already offering reassurance to Merino breeders. Starting in 2005 and scheduled to run for five years on two sites – Armidale (summer rainfall) and Mount Barker in WA, (winter rainfall) – the research will investigate, across a range of environments, the commercial impact and effectiveness of breeding for traits that increase breech-strike resistance. Using sheep sourced from industry in a selective breeding program, the project will measure differences in incidence of breech strike, wool production and cost of production in the resistant and control lines at each site, says project leader Dr Jen Smith, of CSIRO Livestock Industries. A 600-ewe breeding flock has been set up at each site, with three selection lines of 200 ewes each – unselected control (UC), commercial improvement (CI) and plain breech (PB). Half the animals in each selection line will be mulesed and half will remain unmulesed. Twelve rams, sourced from industry or bred within the flock, are used each year – eight PB rams (four each for the PB and CI lines) and four UCs. Two of the rams used each year are common to the NSW and WA flocks, to provide a genetic link, and one ram is used across years to provide an across-year link. The traits of interest include: ú breech and inguinal (crutch) cover; ú breech, body and neck wrinkle; ú dag score; ú worm egg count; ú urine stain; and ú wool traits, such as colour and fibre diameter variability. The information gathered will be used to develop best-practice guidelines for incorporating breech traits into Merino breeding programs. Data collected will also enable estimation of heritability of the indicator traits and correlations between those traits and production traits. This will make possible the estimation of ASBVs (Australian Sheep Breeding Values) for breech and wrinkle traits. “Over the 2006-07 summer, the proportion of 2005-drop ewes affected by breech strike was not significantly different between the unselected control and the breech trait selected lines,” Dr Smith says. “However, in the 2006-drop lamb/weaners the incidence of breech strike in the unselected control line was significantly higher than in the selected lines – 19 per cent compared with four per cent. Unmulesed animals in the selected lines achieved a similar level of protection from breech strike to mulesed animals in the unselected line, with 3.8 per cent versus 3 per cent breech strike. Importantly, flystrike rates across the selection lines in the Armidale flock over the current (2007-08) summer are showing a similar trend to the previous season.” Urine stain has already been identified as causing greater susceptibility to flystrike, with 32 per cent of females in the 2006-drop ewe weaners affected, compared with 19 per cent of males. toWards a breeding solution A major research project to investigate the effectiveness of breeding for traits that increase breech strike resistance is producing some encouraging results Early results in the Armidale flock indicate that of all the breech traits examined, breech strike was most closely associated with breech wrinkle. This may simply be due to relatively lower expression of the breech cover trait in fine and superfine wool flocks than in medium wools. The ‘best’ breech strike resistance traits to focus on may vary depending on factors such as environment, production system and enterprise. In WA, a similar flystrike result was achieved in 2006 where, of the mulesed sheep, 3.5 per cent of genetICs dr Jen Smith, of cSIro Livestock Industries at chiswick, with one of the naturally bare-breeched rams being used to assess the genetic potential of breeding bare-breeched Merinos that do not need mulesing. PhotoS: MAttheW cAWood Beyond the BALe roAd to 010 SuPPLeMent Where to start Growers looking to make genetic gain through any type of selection need to have clear and well- defined breeding objectives and source rams from studs with the same objectives. A growing number of studs have stopped mulesing their sheep. When breeding for flystrike resistance the following traits are particularly important: ú plain body (minimal body and breech wrinkle as well as a bare breech); ú white wool (as wool colour is an indicator of other conditions that will predispose sheep to flystrike, such as fleece rot); ú good ‘nourishment’ (wax content and good, but not excessive, suint levels in the wool); ú low fibre-diameter variation; ú water-repelling staple structure; ú reduced scouring and good internal parasite resistance; ú low fleece rot and ‘dermo’; and ú sound confirmation on the withers. A good place to start with breech and wrinkle traits is in your own flock. All flocks show variation among animals in characteristics that make them less susceptible to flystrike, so growers should look at their flocks and assess the genetic strengths of their animals to fit into the breeding strategy they are adopting. the new Visual Sheep Scores guide, available free from the AWI helpline (1800 070 099), can help growers with some basic classing strategies within their own flocks. there is great long-term benefit in selecting and culling rams and ewes according to their
Apr - May 08
Jun - July 08