FOLLICLE ABNORMALITIES AND FIBER SHEDDING IN MERINO WEANERS FED DIFFERENT LEVELS OF NUTRITION

A study was conducted to examine the relationship between fibre sheddi ng and staple strength in Merino weaners genetically different in stap le strength and fed different levels of nutrition. Fibre shedding at t he point of break along the staple was estimated using 3 different tec hniques: (i) a subjective scoring system of wool follicle activity, ba sed on their morphology in transverse skin sections; (ii) the number o f fibres with club-ends after differential staining to identify remnan ts of the shed-follicle bulb; and (iii) changes in the number of fibre s in the cross-section along individual staples. Irrespective of the t echnique used, the estimated proportion of shed fibres did not differ significantly between the sheep bred for sound and tender wool, but in creased significantly (P < 0.05) in response to adverse nutritional co nditions. Across all treatments, there was a significant (r(2) = 0.63; P < 0.001) correlation between the proportion of shutdown follicles a nd the percentage decrease in the number of fibres in the staple cross -section, although the average difference between the techniques was 1 1.5%. Both techniques indicated that, on average, about 30% of the tot al follicle population became inactive and shed their fibre under the most adverse nutritional conditions, and that this was as high as 50-6 0% for some individual sheep. Neither of these techniques was closely correlated to the proportion of fibres with club-ends (r(2) = 0.15 and 0.20, respectively; P < 0.01). The proportion of shutdown follicles a nd the percentage decrease in the number of fibres in the staple cross -section explained 54% and 52% of the variance in staple strength, res pectively, compared with only 19% explained by the percentage of fibre s with club-ends at the point of break. However, as fibre shedding fai led to remove any variance in staple strength additional to that alrea dy attributed to along- and between-fibre changes in diameter, it is c oncluded that fibre shedding per se does not contribute significantly to nutritional-induced differences in staple strength.