Intrinsic Curvature in Wool Fibres is Determined by the Relative Length of Orthocortical and Paracortical CellsHair curvature underpins structural diversity and function in mammalian coats, but what causes curl in keratin hair fibres? To obtain structural datato determine one aspect of this question, we used confocal microscopy to provide in situ measurements of the two cell types that make up the cortex of merino wool fibres, which was chosen as a well-characterised model system representative of narrow diameter hairs, such as underhairs. We measured orthocortical and paracortical cross-sectional areas, and cortical cell lengths, within individual fibre snippets of defined uniplanar curvature. This allowed a direct test of two long-standing theories of the mechanism of curvature in hairs. We found evidence contradicting the theory that curvature results from there being more cells on the side of the fibre closest to the outside, or convex edge, of curvature. In all cases, the orthocortical cells close to the outside of curvature were longer than paracortical cells close to the inside of the curvature, which supports the theory that curvature is underpinned by differences in cell type length. However,the latter theory also implies that, for all fibres, curvature should correlate with the proportions of orthocortical and paracortical cells,and we found no evidence for this. In merino wool, it appears that the absolute length of cells of each type and proportion of cells varies from fibre to fibre, and only the difference between the length of the two cell types is important. Implications for curvature in higher diameter hairs,such as guard hairs and those on the human scalp, are discussed.
- On completion of this topic you should be able to: • demonstrate an understanding of fibre diameter and the economic importance of fibre diameter • explain and calculate the difference between the standard deviation of diameter and the coefficient of variation of diameter • define the relationship between mean diameter, diameter variation and “coarse edge” or “prickle” • measure staple strength and describe its economic importance • explain the sources of variation in staple strength within a mob of sheep • describe localised vs generalised fibre weakness as determinants of staple strength • define and quantify the relationship between staple strength and each of minimum diameter, along-staple diameter variation, rate of change in diameter, fibre length variation and intrinsic fibre strength • relate raw wool style including the main component traits to economic importance • explain the influence of fibre diameter and fibre crimp on wool handle • describe fibre curvature and the value of curvature
Relationships Between Skin Follicle Characteristics and Fibre Properties of Suri and Huacaya Alpacas and Peppin Merino SheepWe aimed to quantify the number, type and arrangement of skin follicles in Huacaya and Suri alpaca skin and correlate their follicle characteristics with fibre traits of harvested fibre and compared these relationships with those of Merino sheep. Fibre and skin samples were collected from the mid-side of 12 Huacaya alpacas, 24 Suri alpacas and 10 Merino sheep. The mean fibre diameter (MFD ± s.e.) of the Huacaya and Suri were: 35.5 ± 0.9 and 28.3 ± 1.0 μm, respectively. The follicle groups found for alpacas were very different from the normal trio of primary follicles found in sheep and goats. The follicle group of the alpacas consisted of a single primary follicle surrounded by a variable number of secondary follicles. The mean ± s.e. primary follicle density was 3.1 ± 0.3 and 2.7 ± 0.1 follicles/mm2 for Huacaya and Suri, respectively. The mean ± s.e. secondary follicle density (SFD) was 13.7 ± 1.2 and 17.5 ± 0.6 follicles/mm2 for Huacaya and Suri, respectively. The mean ± s.e. ratio of secondary to primary follicles (S/P ratio) was 5.1 ± 0.5 for the Huacaya and 7.3 ± 0.2 for the Suri alpacas. The sheep had higher S/P ratios and SFD, lower MFD and produced significantly heavier fleeces. The key correlations found between traits in alpacas include a negative correlation between SFD and MFD (r = –0.71, P = 0.001) and a negative correlation between S/P ratio and MFD (r = –0.44, P = 0.003) and a positive correlation between S/P ratio and total follicle density (r = 0.38, P = 0.010). The study revealed that important relationships exist between alpaca skin follicle characteristics and fibre characteristics. It was the number of secondary follicles in a group that imparts density and a corresponding reduced MFD.
- The capability of instruments such as SIROLAN-LASERSCAN (LASERSCAN) and OFDA100 to provide measurements of fibre curvature has resulted in increased interest, within Australia among wool producers and exporters, and among overseas top-makers and spinners. However, the metrology of fibre curvature measurement by these instruments is poorly understood. Standardized conditions for preparation, and measurement procedures that stabilize the curvature of the wool fibres prior to measurement by either instrument, are yet to be defined.
- With the increased interest in the measurement of fleece samples from alpacas, a number of questions have been raised concerning the meaning of mean fibre curvature on these samples. Whilst some information has been published, there appear to be some divergent views expressed on the importance of this measurement. This bulletin is intended to impart some factual information which may be useful to growers trying to understand the measurement.