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The History & the Science of the SRS® Breeding System

In the 1970s and 80s, young CSIRO scientist Dr Jim Watts looked into how wool was formed in skin follicles. It was that work that led Dr Watts to conclude that the characteristics the sheep industry was selecting for were wrong. He noted that the "follicles", structures from which the wool fibres grow, varied significantly in diameter and arrangement between animals. In all animals, the follicles were clustered together in "follicle groups", the basic unit of fleece structure beyond the individual fibre, and these follicle groups were repeated throughout the skin of the animal. But just as the individual follicles varied between animals, so too did the follicle groups. Some sheep had many more follicles per follicle group, and others had follicle groups which were more closely packed together, which combined to produce what he described as "increased follicular density."

It had long been understood that there were two types of follicles. The primary follicle which is the first to appear in the skin during foetal development. In alpaca it currently produces a fibre that is generally coarser, grows longer, and is more brittle. In primitive fleece types, it produces a visibly longer and coarser fibre that we recognise as a "guard hair", which is an undesirable feature in woollen textiles. Called variously primary fibre, guard hair or kemp, it is typically a hollow, or "medullated", fibre. In every follicle group, there are three primary follicles.

The rest of the follicles in a follicle group are called secondary follicles, these produce fibres which appear slightly later in foetal development (hence the "halo" of long primaries surrounding the more numerous and shorter secondary fibres in the new-bom). These are smaller diameter fibres than the primaries, but more numerous. They are generally responsible for all the characteristics that are considered desirable in natural fibre, such as lustre, softness, ease of processing and dye uptake

Dr Watts made two profound observations. He noted that follicular density (the number of follicles per square mm) varied widely between sheep. Furthermore, the ratio of secondary to primary follicles within a follicle group (the S/P ratio), also showed wide variation between sheep. That is to say, some sheep were producing many more fibres than others over the same area of skin, whilst others were producing many more of the desirable secondary fibres compared to the number of primaries.

More fibres in a given area of skin.

In many instances, the sheep demonstrating these characteristics were one and the same! That is, they were producing more fibres in a given area of skin than other sheep, and the increased number of fibres was overwhelmingly in favour of the desirable secondary fibres.

Next, Dr Watts looked at the fleeces of those animals. He was able to identify several visual markers that could enable him to identify those sheep showing increased follicular density and increased S/P ratio.

Firstly, and most importantly, the fibres tended to be finer! So here was a potential to increase productivity by simultaneously increasing fleece quantity (number of fibres) and quality (low fibre diameter).

Secondly, they grew faster: at any stage of fleece growth, they were longer than those grown on animals without the same visual markers: more quantity.

Lastly, he also noted that the fibres were very highly aligned, and clustered together in thin bundles that were much smaller than the traditional clump, or "staple". Closer examination of the bundles showed that the wavy pattern we call "crimp" was much more exaggerated than that which had been traditionally sought after for fine wool, a feature which Jim describes as being both a "bolder" and "deeper" crimp.

Bold and deep crimp.

Fibres crimp at more or less regular time intervals. Consequently wools with high crimp frequency (fine crimping) consist of slow growing fibres that produce short fleeces. On the other hand low crimp frequency wools with high amplitude (deep, bold crimp) are fast growing fibres that produce long fleeces. Which shows that high frequency crimp equals poor fibre growth rate and it is also know that it has little to do with the micron of the fibre.