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Abstract
A theoretical model for the tensile strength of staples of wool was used to propose variables that could be measured on thirty six fleece samples from Romney sheep genetically selected on the basis of wool staple tenacity. Other variables that have been noted elsewhere in the literature were also measured. Nearly 75% of the variation in staple tenacity was described by average and minimum cross-sectional area of the fibres, and the relaxed length of the fibres held between the jaws of the instrument used to break the staple. The addition of staple length and variation in total length of the fibres in the staple improved this to almost 84%. The ultimate goal of the genetic selection was to increase the average length of fibres following carding (Hauteur and Barbe), which were also measured on the fleece samples, and the fibre, staple and sample measurements used in stepwise regression to reveal the determinants of length after carding. Variation in Hauteur was dependent on the total energy required to break the staple and the proportion of new tips present in the post-break region of the staple, yet as little as 52% of the variation was accounted for. Average cross-sectional area accounted for a further 3% of the variation in Hauteur but this was not statistically significant. Barbe was dependent on staple tenacity, which accounted for 48% of the variation. In hindsight, staple tenacity may not be an appropriate measure to genetically select sheep in order to improve fibre length after carding given the variables that affect these traits.
Acknowledgements
The author is grateful to the large number of staff and students required to undertake this work. Andy Bray and Malcolm Smith helped obtain the wool at shearing time. Norma Merrick measured medullation in the samples and assisted with collection. Jason Daly measured fibres on the OFDA along fibre machine and calculated the parameters from this instrument. Simon Williamson measured the length of fibres between the jaws. Cushla O’Connell laid out individual fibres on adhesive tape for Denis O’Connell to measure fibre length. Ian Gittins and Andrew Peterson of the Department of Agriculture Western Australia conducted the SIFAN measurements. Leila Markham estimated the number of fibre breaks, new tips and shed ends. Duane Harland provided the image of the elliptical fibre. The statistical analyses were performed by David Baird.
Disclosure statement
No financial benefit has arisen from the application of this research.