- Genetic parameters (heritability, phenotypic and genetic correlations) were estimated for a range of visual and measured wool traits recorded from the 2008 shearing of the initial cohort of Merino progeny born into the Sheep CRC’s Information Nucleus Flock. The aim of this initial analysis was to determine the feasibility of selectively breeding Merino sheep for softer, whiter, more photostable wool and to quantify the likely impact on other wool production and quality traits. The estimates of heritability were high for handle and clean colour (0.86 and 0.70, respectively) and moderate for photostability (0.18), with some evidence of maternal effects for both handle and photostability. The phenotypic correlations between handle and clean colour and between handle and photostability were close to zero, indicating that achieving the ‘triple’ objective of softer, whiter, more photostable wool in the current generation through phenotypic selection alone would be difficult. There was evidence of an antagonistic relationship between handle and photostability (–0.36), such that genetic selection for softer wool will produce less photostable wool that will yellow on exposure to UV irradiation. However genetic selection for whiter wool is complementary to photostability and will result in whiter wool that is less likely to yellow. Genetic selection to improve handle, colour and photostability can be achieved with few detrimental effects on other visual and measured wool traits, particularly if they are included in an appropriate selection index.
Effect of Selection for Wool Growth on Seasonal Patterns of Yield, Fibre Diameter, and Colour in Romney LinesSeasonal wool growth and associated wool characteristics were measured in a Romney line selected for high fleece weight and an unselected control line in 1990 and 1991. Both had a significant (P < 0.01) decline in wool growth rate in winter compared with summer. The wool growth rate advantage (P < 0.001) of the selected line over the control averaged 19 and 33% for ewes, and 24 and 36% for hoggets, in summer and winter, respectively. Staple strength, yield, and fibre diameter differences were closely associated with wool growth. Colour analysis showed no difference between lines in either brightness (Y) or yellowness (Y - Z). However, both the Y and Z values were lower in spring and summer, while Y - Z was highest in summer. The results suggest that selection for high fleece weight also improves major wool characteristics and reduces the relative winter wool growth decline in Romneys.
Sire Genetics, Protein Supplementation and Gender Effects on Wool Comfort Factor in Australian Crossbred SheepAims: To investigate the effects of sire genetics, nutrition, level of supplementation, gender and their interactions on wool comfort factor (CF) and its correlation with other wool quality traits in crossbred sheep either grazing or supplemented with dietary protein. Study design: A 5 x 2 x 2 x 2 factorial experimental design comprising five sire breeds, two dietary protein sources, two supplementation levels and two sexes respectively, was utilized. Place and Duration of Study: University of Tasmania Farm, Cambridge, Hobart, Tasmania, Australia, between April 2008 and November 2010. Methodology: Texel, Coopworth, White Suffolk, East-Friesian and Dorset sires were joined with 500 Merino ewes at a mating ratio of 1:100 in individual paddocks. Five hundred of the crossbred progeny were raised on pastures until weaning at 12 weeks of age. Forty of the weaners with an initial body weight (BW) range of 23-31 kg (average of 27 ± 3.2 kg) were fed with lupins or canola at 1 or 2% BW for 6 weeks in individual metabolic crates. CF and other wool quality traits were commercially measured at the Australian Wool Testing Authority, Melbourne. The data were analyzed in SAS using MIXED model procedures with sire fitted as a random effect, while sire breed, nutrition, supplement, level of supplementation and gender and their interactions were fitted as fixed effects. Results: CF was significantly correlated with fiber diameter (-0.89), spinning fineness (-0.95) and wool curvature (0.33). Grass-fed sheep produced wool with significantly higher comfort factor (93.1±0.3%) than supplemented sheep (CF=85.9±1.1%). Sire genetics was a significant source of CF variation; White Suffolk crosses had the highest CF (90.1±8.7) and East-Friesian crosses the least (81.5 ± 10.1%). Males fed canola at 1%BW had the highest CF (90.8 ± 7.0%), while females fed lupins at 1% BW had the least (81.1±10.8%). Conclusion: From a practical point of view, sheep farmers engaging in prime lamb production with wool comfort factor as an additional breeding objective should concentrate their effort on grass-feeding White Suffolk x Merino wethers. During the winter feed gap, supplementing the wethers with canola at 1% BW will not compromise wool CF.
- The opportunity exists to utilise our knowledge of major genes that influence the economically important traits in wool sheep. Genes with Mendelian inheritance have been identified for many important traits in wool sheep. Of particular importance are genes influencing pigmentation, wool quality and the keratin proteins, the latter of which are important for the morphology of the wool fibre. Gene mapping studies have identified some chromosomal regions associated with variation in wool quality and production traits. The challenge now is to build on this knowledge base in a cost-effective way to deliver molecular tools that facilitate enhanced genetic improvement programs for wool sheep.
Use of Part Records in Merino Breeding Programs - The Inheritance of Wool Growth and Fibre Traits During Different Times of the Year to Determine Their Value in Merino Breeding ProgramsFibre diameter can vary dramatically along a wool staple, especially in the Mediterranean environment of southern Australia with its dry summers and abundance of green feed in spring. Other research results have shown a very low phenotypic correlation between fibre diameter grown between seasons. Many breeders use short staples to measure fibre diameter for breeding purposes and also to promote animals for sale. The effectiveness of this practice is determined by the relative response to selection by measuring fibre traits on a full 12 months wool staple as compared to measuring them only on part of a staple. If a high genetic correlation exists between the part record and the full record, then using part records may be acceptable to identify genetically superior animals. No information is available on the effectiveness of part records. This paper investigated whether wool growth and fibre diameter traits of Merino wool grown at different times of the year in a Mediterranean environment, are genetically the same trait, respectively. The work was carried out on about 7 dyebanded wool sections/animal.year, on ewes from weaning to hogget age, in the Katanning Merino resource flocks over 6 years. Relative clean wool growth of the different sections had very low heritability estimates of less than 0.10, and they were phenotypically and genetically poorly correlated with 6 or 12 months wool growth. This indicates that part record measurement of clean wool growth of these sections will be ineffective as indirect selection criteria to improve wool growth genetically. Staple length growth as measured by the length between dyebands, would be more effective with heritability estimates of between 0.20 and 0.30. However, these measurements were shown to have a low genetic correlation with wool grown for 12 months which implies that these staple length measurements would only be half as efficient as the wool weight for 6 or 12 months to improve total clean wool weight. Heritability estimates of fibre diameter, coefficient of variation of fibre diameter and fibre curvature were relatively high and were genetically and phenotypically highly correlated across sections. High positive phenotypic and genetic correlations were also found between fibre diameter, coefficient of variation of fibre diameter and fibre curvature of the different sections and similar measurements for wool grown over 6 or 12 months. Coefficient of variation of fibre diameter of the sections also had a moderate negative phenotypic and genetic correlation with staple strength of wool staples grown over 6 months indicating that coefficient of variation of fibre diameter of any section would be as good an indirect selection criterion to improve stable strength as coefficient of variation of fibre diameter for wool grown over 6 or 12 months. The results indicate that fibre diameter, coefficient of variation of fibre diameter and fibre curvature of wool grown over short periods of time have virtually the same heritability as that of wool grown over 12 months, and that the genetic correlation between fibre diameter, coefficient of variation of fibre diameter and fibre curvature on part and on full records is very high (rg > 0.85). This indicates that fibre diameter, coefficient of variation of fibre diameter and fibre curvature on part records can be used as selection criteria to improve these traits. However, part records of greasy and clean wool growth would be much less efficient than fleece weight for wool grown over 6 or 12 months because of the low heritability of part records and the low genetic correlation between these traits on part records and on wool grown for 12 months.