Deep crimp (high crimp amplitude) is the outcome of high fibre (follicle) density. It signals that the fleece fibres are highly aligned and each fibre is fine in diameter and uniform in diameter, length and shape. The fibre shape is cylindrical with a smooth surface (low scale height). The internal structure of the Huacaya (and Merino) fibre from a deeply crimped animal is arranged as hemi-cylinders of orthocortex ('soft' keratin) and paracortex ('hard' keratin), creating balanced bending forces which allow the fibre to form a deep crimp arc and imbuing the fibre with high elasticity. The high content of orthocortex, the dye-accessible side of the fibre, contributes to the excellent dyeing results obtained with deeply crimped wools. Suri fibre has a different arrangement of orthocortex and paracortex which produces coiling, rather than crimping, of the fibre but the density-induced changes in fibre morphology are the same. In both cases, the staples are very thin an never thick or solid.

When deep crimp is combined with bold crimp (low crimp frequency), the fibres are long (fast growing). Whilst fleece length is visually obvious, fibre length is not. Fibre length to staple length ratio can vary from about 1.0 to 1.5 in Merino wools. The deeper the crimp is, the more likely this ratio is to be close to 1.5, and vice versa. As the wool becomes bolder crimped whilst maintaining deep crimp, the scales on the fibre surface are not only low in height but also spaced further apart - the nett result being the feeling of exquisite softness and smoothness of fabric against our skin.

The objective of the SRS® breeding system is to select for high levels of fibre density and fibre length as the means of delivering high fleece weight and low fibre diameter as well as improved fibre quality. The selection methods are based on Moore's pre-papilla cell studies of the regulation of wool follicle formation and fibre size (see Moore et al,1998;www.srswool.com.

Fibre density, fibre length and fibre diameter are controlled by genes that regulate the number, distribution and signal strength of the wool-follicle forming pre-papilla cells in the foetal skin.

Pre-papilla cells have to fill the 'initiation sites' (primary follicles and original secondary follicles) before secondary follicle branching occurs. If there are more 'initiation sites' to fill (akin to more 'guard hair'), and these are filled with large clusters (akin to coarse 'guard hair') secondary follicle branching is less likely to occur, and vice versa.

Stevens and Crowe (1994) showed that for Merino wools of the same fibre diameter, fleece length, tensile strength, yield and vegetable matter content, those wools with deep and bold crimp made tops that were 8 to 16 millimetres longer with approximately half the noil and card waste of wools of less defined and 'finer' crimp. Longer Hauteur (mean fibre length) tops spin more efficiently and produce yarns that are more even and break less often (Yang, 1993; Lamb and Yang, 1996). For each decrease of one crimp per centimetre or one grade improvement in crimp definition, Hauteur improves by 4 millimetres. These effects are separate and additive. A 4 millimetre increase in Hauteur is equivalent to a reduction of 0.4 microns in fibre diameter, or 8 Newtons per kilotex better staple strength.

Very few wool processors have been in a position to obtain large and regular quantities of deep and bold crimping Merino wools, and of course, alpaca wools, to meet their milling requirements. The supply shortage is at farm level where these deep and bold crimping wools are not being bred in sufficient quantities. Consequently, it is understandable why processors are generally unaware of the findings of Stevens and Crowe and others. It is also understandable why processors at a recent IWTO meeting were not prepared to endorse fibre curvature, a method of measuring amplitude and frequency of crimp, and why it is yet to have any influence on raw wool price. These benefits are yet to be discovered at commercial level by the wool trade.

It is also no surprise to hear that fibre diameter still influences 73% of the decision making on the price of raw wool. Selection for high density (and length) is a powerful way of genetically reducing fibre diameter. High density is a consequence of a large starting population of pre-papilla cells in the foetal skin being distributed as small clusters. The small cluster of pre-papilla cells that comes to reside in the dermal papilla of the follicle is responsible for the follicle producing a fine diameter fibre.

So there are choices in how to breed for low fibre diameter. You can choose to produce low diameter wools on animals of high fleece weights or low diameter wools on animals of low fleece weights. If the former is your goal, select for very long, thin staples with a deep and bold crimp. If the latter is your goal, select for high crimp frequency ('fine' crimp) fleeces. If you would prefer to select for thick staples (the 'productive looking' fleece) then you will find it impossible to produce large numbers of animals with sustainably low fibre diameter, regardless of your preference on crimp.

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