WOOL FIBER TENACITY IN ROMNEY SHEEP GENETICALLY DIFFERENT IN STAPLE TENACITY

Wool from lines of Romney sheep selected for improved or reduced stapl e tenacity was examined to determine if the difference in staple tenac ity was explained by a difference in fibre tenacity. A random sample o f ewe hogget wools (n = 32) was chosen from each of the 2 selection li nes. 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 a rea of the fracture surface. Staple tenacity was measured on 5 staples per sample, by placing each staple in a Staplebreaker set to 40 mm be tween clamps, and the peak force to break the staple was recorded. Pri or to clamping, each staple was adjusted so that the thinnest point me asured 1.5 mm(2) in cross-section and this point was positioned 20 mm from each clamp. Although the difference in staple tenacity between th ese 2 groups was highly significant (P = 0.002), there was no differen ce in the tenacity of individual fibres (P = 0.903). Staple tenacity w as not significantly correlated with fibre tenacity (r = 0.090). Simil arly, there was no significant correlation between work to break the s taple and either work (r = 0.118) or peak force (r = 0.195) to break t he fibre. It is proposed that other components of staple tenacity, suc h as the profile of cross-sectional area along the fibre and the varia bility of crimped fibre length within the staple, may be more importan t determinants of staple tenacity in these selection lines.