Follicle characteristics, seasonal changes in fibre cross-sectional area and ellipticity in Australasian specialty carpet wool sheep, Romneys and Merinos

Data was collected on secondary:primary follicle ratio, relative follicle d ensity, and seasonal changes in fibre cross-sectional area and fibre ellipt icity (ratio of major-to-minor fibre cross-sectional axis) in the Australas ian specialty carpet wool breeds (Carpetmaster, Drysdale, Elliottdale, Tuki dale), Romneys and Merinos. Merinos had a higher secondary:primary follicle ratio (p<0.001), relative primary follicle density (p<0.05), relative seco ndary and relative total follicle density (p<0.01) than the other breeds. B oth breed and follicle type (primary or secondary) had a significant effect on fibre cross-sectional area (p<0.05). While both fibre types (primary an d secondary) showed changes in cross-sectional area during the experiment, a more distinct seasonal pattern was seen in the secondary fibres with summ er maxima and winter minima in all breeds. Relative change in fibre diamete r was higher in secondary fibres than in primary fibres. Changes in fibre e llipticity were also noted throughout the duration of the experiment. It is apparent that there are differences between primary and secondary follicle populations in the way the fibres produced contribute to seasonal changes in average fibre diameter of fleeces. The changes suggest there are separat e control mechanisms for each follicle type and that the number, size and a rrangement of the cells in each type of fibre vary independently of one ano ther throughout the year, bringing about dynamic changes in fibre growth an d form. Further work is required to examine the influence of feed quality o n these factors and to determine the mechanisms through which these changes in fibre structure are brought about. (C) 2000 Elsevier Science B.V. All r ights reserved.