Unravelling Staple Strength

A wool staple is an independent natural cluster of fibres not a single fibre. Very many staples together form a fleece. Staple length, a property of staple fibres, is a term referring to the average length of a group of fibres of any composition. Staple length depends on the origin of the fibres. 

Natural fibres (such as cotton or wool) have a range of lengths in each sample, so the staple length is an average. Staple length generally determines the end use of wool, that is, whether it will be used in weaving or knitting.

After mean fibre diameter, Staple Strength is the second most important raw wool trait in determining wool price. The staple strength of wool is one of the major determining factors when spinning yarn. But improving staple strength by genetic and nutritional means has proven to be less straightforward than first thought. Staple strength is essentially a measurement of material strength, with no simple biological basis. While SS is a very useful predictor of the processing performance of wool fibres, its usefulness for selecting sheep is limited by cost. For this reason researchers have looked for alternative indicators of SS which might be useful in breeding programs.                                                                          

Fine Wool 

One of the most promising indicators is the total variation in fibre diameter generated by both ‘along-fibre variations’ and ‘between fibre variations’. This variation is measured at the same time as Mean Fibre Diameter and is expressed as the Coefficient of Variation of Fibre Diameter (CVFD), which is simply the standard deviation of fibre diameter divided by the mean fibre diameter (and expressed as a %). Sheep with a high CVFD tend to produce wool with a low SS. This created great excitement because for the first time we could select sheep with a low CV and thus a high SS. Seasonal conditions or the health of the sheep may influence the soundness (strength) of the wool.

There are several factors, which can reduce the staple strength of a clip.

By identifying the position of break, it is possible to establish when the weakening of the fibre occurred and therefore what management practices of climatic conditions contributed to the weakening. Poor nutrition, dramatic changes in diet, diseases and internal/ external parasites can all affect the tensile strength of wool.