Follicle abnormalities and fibre shedding in Merino weaners fed different levels of nutrition

Abstract

A study was conducted to examine the relationship between fibre shedding and staple strength in Merino weaners genetically different in staple strength and fed different levels of nutrition. Fibre shedding at the point of break along the staple was estimated using 3 different techniques: (i) a subjective scoring system of wool follicle activity, based on their morphology in transverse skin sections; (ii) the number of fibres with club-ends after differential staining to identify remnants of the shed-follicle bulb; and (iii) changes in the number of fibres in the cross-section along individual staples. Irrespective of the technique used, the estimated proportion of shed fibres did not differ significantly between the sheep bred for sound and tender wool, but increased significantly (P < 0·05) in response to adverse nutritional conditions. Across all treatments, there was a significant (r2 = 0·63; P < 0·001) correlation between the proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section, although the average difference between the techniques was 11·5%. Both techniques indicated that, on average, about 30% of the total follicle population became inactive and shed their fibre under the most adverse nutritional conditions, and that this was as high as 50–60% for some individual sheep. Neither of these techniques was closely correlated to the proportion of fibres with club-ends (r2 = 0·15 and 0·20, respectively; P < 0·01). The proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section explained 54% and 52% of the variance in staple strength, respectively, compared with only 19% explained by the percentage of fibres with club-ends at the point of break. However, as fibre shedding failed to remove any variance in staple strength additional to that already attributed to along- and between-fibre changes in diameter, it is concluded that fibre shedding per se does not contribute significantly to nutritional-induced differences in staple strength.