Wool fibre tenacity in Romney sheep genetically different in staple tenacity

Abstract

Wool from lines of Romney sheep selected for improved or reduced staple tenacity was examined to determine if the difference in staple tenacity was explained by a difference in fibre tenacity. A random sample of ewe hogget wools (n = 32) was chosen from each of the 2 selection lines. Fibre tenacity was measured by breaking 10 fibres from each wool sample using an Instron to measure peak force, and then a fluorescence microscope attached to an image analyser to measure cross-sectional area of the fracture surface. Staple tenacity was measured on 5 staples per sample, by placing each staple in a Staplebreaker set to 40 mm between clamps, and the peak force to break the staple was recorded. Prior to clamping, each staple was adjusted so that the thinnest point measured 1.5 mm2 in cross-section and this point was positioned 20 mm from each clamp. Although the difference in staple tenacity between these 2 groups was highly significant (P = 0.002)) there was no difference in the tenacity of individual fibres (P = 0.903). Staple tenacity was not significantly correlated with fibre tenacity (r = 0.090). Similarly, there was no significant correlation between work to break the staple and either work (r = 0.118) or peak force (r = 0.195) to break the fibre. It is proposed that other components of staple tenacity, such as the profile of cross-sectional area along the fibre and the variability of crimped fibre length within the staple, may be more important determinants of staple tenacity in these selection lines.