ABNORMAL SHEDDING CONTRIBUTES TO THE REDUCED STAPLE STRENGTH OF TENDER WOOL IN WESTERN-AUSTRALIAN MERINOS

The role of fibre shedding in tender wool was investigated in 65 Weste rn Australian Merino fleeces (staple strengths ranging from 3.6 to 77. 0 N/ktex). The percentage of shed fibres ranged from 0 to 36% of the f ibres at the point of break in the staple. There was a significant exp onential relationship (P<0.001) between staple strength and the propor tion of shed fibres in wool staples from wethers and non-supplemented ewes in late pregnancy and lactation. However, this exponential relati onship was not maintained in ewes when supplemented with methionine or a combination of valine, arginine, lysine and threonine in late pregn ancy and early lactation. The correlation between staple strength and fibre diameter coefficient of variation was weaker in wethers (r(2)=0. 47) than previously reported and was not significant for the reproduci ng ewes. Except for some occasional thick hair-like fibres which were present in the staple, the shed fibres examined did not terminate in t ypical telogen stage brush ends. Scanning electron microscope analysis revealed that these fibres terminated in long club-shaped structures, which were probably shed at catagen stage 5 of the hair growth cycle. Internally, keratinisation was incomplete in the terminal cortical ce lls of these clubs as well as in the covering sheath of probable inner root sheath cells. The results indicate that fibre shedding is a sign ificant component of tender fleeces in Western Australia Merinos.