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Lecture 2: Fleece Weight and its Component Traits and Fibre Diameter

Tony Schlink

Learning Objectives On completion of this topic you should be able to:

describe and quantify the relationships between fleece weight, washing yield and the non-fibre components of the fleece

explain the relationship between clean fleece weight and its component traits describe the sources of variation and within-fleece gradients in the fibre and non-fibre

components of the fleece justify the merits of the mid-side region of the fleece for flock testing purposes identify non-genetic factors that may introduce bias into selection decisions based on fleece

weight and its component traits demonstrate and 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

Key terms and conceptsGreasy fleece weight; yield; clean fleece weight; non-fibre components; suint; wax; dust; vegetable matter; within fleece gradients; component traits; body weight; wrinkle score; staple length; fibre diameter; follicle density; non-genetic handicaps; mid-side sample, fibre diameter; coefficient of variation of diameter; standard deviation of diameter; prickle.

Introduction to the topicThis topic will give you an understanding of the factors that contribute to fleece weight, yield and fibre diameter and how the contribution of each differs within and between fleeces as well as discussing how some of the component traits are measured.

2.1 Fleece weight, yield and the non-fibre components of the fleeceThe mass of greasy wool shorn from the sheep, including the belly wool but prior to skirting, is referred to as the greasy fleece weight. This weight represents the combined weight of clean wool fibre, wax, suint, vegetable matter, dirt and dust, and other non-fibre components. This greasy weight is readily obtained if a set of scales is available in the shearing shed. However, from a wool processor’s viewpoint, clean fibre is the commodity of interest, such that for trading purposes yield estimates are routinely obtained, this being the proportion of clean fibre that can be obtained from the greasy wool sale lots. There are a number of yield estimates reported depending on market requirements, but the common estimate is the Schlumberger Dry Combed Top and Noil Yield. This indicates the yield of fibre that can be processed into top, after adjusting for residual contaminants and fibre loss during processing.

For flock testing purposes, a washing yield is used to estimate the clean fibre content of the fleece. This involves a sample of the greasy fleece being weighed, then washed and dried, with the resultant clean, dry weight being expressed as a percentage of the greasy sample weight. No adjustments are made for residual contaminants after scouring. The clean fleece weight is then calculated as follows:

clean fleece weight (kg) = greasy fleece weight (kg) x washing yield (%).

Table 2.1 summarises the phenotypic associations between fleece weight, yield and the non-fibre components of the fleece. While those individuals with the heaviest greasy fleece weights may not produce the highest yielding fleeces, there is a strong tendency for them to be among those with the heaviest clean fleece weights. High yielding fleeces also tend to have relatively lower suint, wax and dust contents. Given the definition of washing yield, it is not surprising to find a lack of a strong correlation with vegetable matter content.

WOOL412/512 Sheep Production 2-1© 2013 The Australian Wool Education Trust licensee for educational activities University of New England

Notes – Lecture 2 – Fleece weight and its component traits and fibre diameter

Table 2.1: Phenotypic correlations between greasy (GFW) and clean (CFW) fleece weights, yield at the mid-side and the suint, wax, dirt and vegetable matter (VM) content in the mid-side sample (Mortimer and Atkins 1989; 1993 and Thornberry and Atkins 1984).

2.2 Sources of variation in yield and the non-fibre components of the fleece

The results summarised in Table 2.2 relate to 4 strains of Merino – one fine, one medium non-Peppin and two medium Peppin strains – maintained as a single flock in one environment. The within-fleece and between-fleece components of variation are expressed as a percentage of the total within-mob variation. Note that these values don’t indicate the actual level of variation, such that a source of variation could account for a large percentage of a very small amount of variation within a mob. These results indicate that between-fleece variation in suint and wax content is greater than within-fleece gradients, whereas within-fleece gradients in dust and vegetable matter are large compared to differences between fleeces.

Table 2.2: Contribution of within- and between- fleece variation to total mob variation for the non-fibre components of the fleece (Thornberry and Atkins 1984).

Component Within-fleece Between-fleeceSuint (%) 36 64Wax (%) 42 58Dust (%) 82 18VM (%) 89 11

The general fleece gradients (Figure 2.1) can be summarised as follows: Suint - shows an increase from back-line to belly. Given its water-soluble nature, this gradient is

likely to reflect the tendency for suint to be leached from the back-line in response to fleece wetting, which would be greater at this site than on the side or belly of the sheep

Wax - shows an increase from mid-side to back-line and from forequarters to hindquarters. This reflects the gradient in follicle density as well as the reduction in the suint content of the mid-side and back-line of the fleece

Dust - is generally greatest along the back-line, reflecting the more open nature of the fleece at this site. Dust content must be measured directly and not estimated from dust penetration (Ladyman et al. 2003)

Vegetable matter - increases towards the breech and belly regions of the fleece, reflecting the proximity of these regions to pasture species that contribute to vegetable fault.

For suint and wax, most sample sites provide a reasonably reliable estimate of the fleece average. For vegetable matter and dust, the within-fleece gradients cause all sites to be less reliable in estimating the fleece average, although the mid-side sample is reasonable for dust. However, no single site provides a reliable estimate of vegetable matter content in the overall fleece.

Considering these gradients, the most reliable sample site for estimation of washing yield, which ignores VM, is the mid-side. This is defined as the site centred on the third last rib, halfway between the mid-line of the back and the mid-line of the belly (Figure 2.2). It is also advised that this should be taken from the left hand side of the animal, given the tendency for sheep to rest on their right side while lying down and the implications for VM and dust (Standards Australia 1997).

2-2 _________________________________________________WOOL412/512 Sheep Production© 2013 The Australian Wool Education Trust licensee for educational activities University of New England

CFW Yield Suint Wax Dust VMGFW 0.87 -0.11 -0.06 0.17 0.03 -0.14CFW 0.37 -0.23 -0.17 0.10 -0.10Yield -0.51 -0.68 -0.74 0.13Suint 0.01 -0.01 -0.02Wax 0.34 -0.49Dust -0.32


(a) Percent suint (grams suint per 100 g conditioned clean wool)

(b) percent wax (grams wax per 100 g conditioned clean wool)

(c) Percent dust (grams dust per 100 g conditioned clean wool)

(d) Percent vegetable matter (grams vegetable matter per 100 g conditioned clean wool)

Figure 2.1: Within-fleece gradients for non-fleece contaminants (Thornberry and Atkins 1984).

Figure 2.2: Location of the mid-side sample site for collection of fleece samples for washing yield (Standards Australia 1997).



2.3 The components of clean fleece weightClean fleece weight (CFW) is a composite characteristic in that it is a function of a number of other characteristics comprising:

those influencing the total wool-growing surface area of the animal, these being body surface area and wrinkling factor, and

those influencing the total weight of wool produced per unit area of wool-growing skin, these being mean fibre density, mean fibre length and mean fibre cross-sectional area.

These individual components of CFW are difficult to measure directly but can be derived for more readily available measurements or scores, as summarised in Table 2.3. In the derivation of mean fibre length, a relationship is assumed between this component, and staple length and fibre diameter coefficient of variation (Schlink et al. 2001) (fibre length (mm) (FL) = -42.1 + 1.08*staple length + 3.01*fibre diameter coefficient of variation). In the derivation of mean fibre cross-sectional area, there is a contribution arising from diameter variation (VD), though for most purposes, ignoring this contribution results in minimal error. Wrinkling factor is the only component not derived from a measured parameter, but instead is derived from a wrinkle scoring system developed by Carter (1943).

Table 2.3: Derivation of CFW components (Turner 1958 and Schlink et al. 2001).

With the exception of follicle density, all component traits have direct economic value in their own right. Body weight influences the sale value of surplus stock, but this must be balanced with the higher feed intakes associated with larger sheep. Highly wrinkled rams have reduced capacity to thermoregulate the scrotum, such that temporary infertility can occur during hot conditions, with implications for flock fertility in some environments when a late summer joining is practiced.

Fibre diameter and staple length have direct effects on wool value. Clean price increases as average fibre diameter declines, such that premiums are paid for finer wool types. In addition, there is an increase in the price differential as fibre diameter decreases, ie. the % change in price from 20m to 19m is greater than the % change in price from 25m to 24m. Thus the relationship between fibre diameter and clean price is curvilinear. There is also a curvilinear trend between staple length and clean price, though different in nature to that for diameter. There appear to be optimum staple lengths such that shorter and longer staple lengths, relative to this optimum length, incur a penalty. The optimum lengths differ for fine, medium and strong wool types and from sale to sale. Also, the penalties tend to be greater for finer wool types.

2.4 Phenotypic associations between clean fleece weight and its components

Changes in clean fleece weight must arise from changes in one or more of its component traits. Table 2.4 summarises the phenotypic associations between CFW and the component traits, indicating the extent to which clean fleece weight and its component traits are likely to change together from sheep to sheep. Within any mob of sheep, those individuals producing a heavier weight of clean wool tend also to be those with the longer staples and heavier body weights. To a lesser extent, they may also show a tendency towards higher fibre diameter and wrinkle score. They may not, however, be the individuals with the highest follicle densities.

On this basis, it is expected that factors which increase clean fleece weight will also give rise to an increase in staple length and body weight, and to a lesser extent, fibre diameter and wrinkle, with little effect on follicle density.


Component trait Derived from DerivationBody surface area Body weight (B) B0.67Smooth surface area Wrinkle score (F) F0.20Mean follicle density Mean fibre density (N) NMean fibre length Mean staple length (L) FLMean fibre cross-sectional area Mean fibre diameter (D) (D2 + VD)/4Fibre density Fibre density (g/cm3) 1.304

Notes – Lecture 2 – Fleece weight and its component traits and fibre diameterTable 2.4: Phenotypic correlations between clean fleece weight and its component traits in fine, medium and broad wool Merino flocks (Swan et al. 1995; Purvis and Swan 1997; Brown and Turner 1968 and Gregory 1982).

Component Fine Medium BroadBody weight 0.44 0.23 0.36Wrinkle score - 0.12 0.20Follicle density 0.04 0.16 0.09Staple length 0.36 0.37 0.32Fibre diameter 0.26 0.14 0.13

This is demonstrated best by way of example. A single mob of young sheep was randomly split into two groups (Morley 1956; Dun 1958). One group (High) was given the best available pastures for grazing and received ad lib cereal hay, oaten grain and meat meal when pasture appeared limiting. The other group (Low) grazed pastures that had been heavily infested with rabbits, with little feed on offer. The groups grazed under these conditions for 12 months. Measurements of clean wool weight, body weight, wrinkle score, follicle density, fibre diameter and staple length were collected at the end of the experiment, when sheep were 18 months of age.

The results are summarised in Table 2.5. Sheep on the high plane of nutrition produced around 40% more clean weight of wool compared to those on the low plane of nutrition. This increase was achieved predominantly through an increase in the weight of clean wool per unit area of skin as well as an increase in the total surface area of wool-bearing skin due solely to an increase in body weight. The increase in clean weight per unit area of skin arose from substantial increases in fibre volume (i.e. diameter and length), offset to some extent by a reduction in fibre density (as the fixed number of follicles were spread over more skin area - thus density declined). There was no significant change in total number of fibres as the increase in smooth surface area was offset by a reduction in fibre density.

Table 2.5: Mean performance for clean fleece weight and its component traits in groups of sheep maintained on either a high or low plane of nutrition, and the difference between the two groups expressed as a percentage of the low nutrition group performance (Dun 1958).

High Low % diff.Clean fleece weight (kg) 4.1 2.9 41Body weight (kg) 40.1 30.8 30Wrinkle score 11.1 11.0 < 1Follicle density (no. per mm2) 33.4 41.3 - 19Staple length (cm) 10.0 9.1 10Fibre diameter (m) 24.2 20.4 19

2.5 Within- and between- fleece variationFigure 2.3 summarises the within-fleece trends evident in Merino sheep for clean wool production per unit area of skin and its component traits, fibre diameter, staple length and follicle density. For the composite trait, there is a significant gradient from the belly to the back-line, and a lesser gradient from hind to forequarters (Figure 2.3a). As to fibre diameter, there is a general antero-posterior gradient, such that the hind section of the fleece is usually the coarsest. Dorso-ventral gradients in diameter are not consistent. Gradients for staple length do not appear to be significant nor consistent. Follicle density, however, shows a large gradient from belly to back-line and from hind to forequarter. Thus differences in wool production per unit area of skin between regions of the body are mainly a reflection of follicle density gradients.

In view of these within-fleece gradients, a choice must be made as to the most appropriate site from which to take a fleece sample for flock testing purposes. As with washing yield, measurements of wool production per unit area of skin, fibre diameter and staple length at the mid-side have the strongest and most consistent correlation with the overall average for the fleece. Other sites can be used for the ranking of animals, provided the sampling site is consistent between animals. For example, some breeders measure diameter at the hip-bones to indicate the “upper limit” of diameter within the fleece, even though it does strongly reflect the fleece average.



(a) clean wool (grams) per cm2 skin (b) mean fibre diameter (m)

(c) mean staple length (cm) (d) mean follicle density (no. per cm2)

Figure 2.3: Within-fleece gradients for clean wool production per unit area of skin and its component traits (Young and Chapman 1958).

Given the direct economic importance of fibre diameter and staple (fibre) length, it is worthwhile considering the sources of variation in these two components in greater details. That is, the relative contributions to total mob variation due to variation between fleeces, variation between sites within a fleece, variation between staples within a site and variation between fibres within a staple.

Table 2.6: Relative contributions to total within-mob variation in fibre diameter, staple length and fibre length (Quinnell et al. 1973; Rottenbury and Andrews 1975; Rottenbury et al. 1980 and Dunlop and McMahon 1974).

Fibre diameter Staple length Fibre lengthWithin fleece

Within staplesBetween staples

84804

66-66

908010

Between fleece 16 34 10

By referring to Table 2.6, it can be seen that there is more variation in fibre diameter, staple length and fibre length within a fleece than there is variation between fleeces within a mob. Furthermore, for fibre diameter and fibre length, there is more variation in diameter and length within a single staple than there is between sheep within a mob.

2.6 Non-genetic handicaps in the clean fleece weight and its components

Non-genetic factors such as age of dam, birth-rearing status and age can significantly affect the performance of young sheep in terms of clean fleece weight and its components. Table 2.7 represents the penalty in hogget performance (12-18 months age) arising from having a maiden dam, being born and raised as a multiple lamb and being born late in the lambing period. For example, sheep born to maiden ewes will have 2% lower clean fleece weight on average at hogget shearing compared to those born to adult ewes. Those born as multiples will have 7% lower fleece weight compared to their single-born contemporaries. Those born at the end of a 5 week lambing period will have 11% lower fleece weight compared to those born at the start of lambing. In general, these handicaps impact on fleece weight and the component traits in much the same way, except possibly for fibre diameter and follicle density.



These handicaps constitute a potential source of bias at selection. In other words, the genetic merit of an individual may be over- or under- estimated due to its performance being (dis)advantaged by one or more of these non-genetic factors. We expect, for instance, that an individual of high genetic merit for wool production would not perform phenotypically as well as unhandicapped individuals of lower merit if it had been born to a maiden dam, was born and raised as a multiple and had been born late in the lambing period. It’s performance would be penalised!

Table 2.7: Possible handicaps in hogget performance for clean fleece weight and its component traits, arising from dam age, birth-rearing status and age. Each handicap is expressed as the difference as a percentage of either maiden, multiple-reared or youngest age (Mortimer and Atkins 1989; 1993).

Maiden vs adult dam

Multiple- vs single-reared

Youngest vs oldest (5 week lambing)

Clean fleece weight -2% -7% -11%Body weight -2% -4% -7%Wrinkle score -9% -29% -15%Follicle density -1% -3% -5%Staple length 0% -2% +4%Fibre diameter 0% +2% -2%

Substantial annual variation in flock average performance exists for all components of clean fleece weight. However, annual variation in clean wool per head is largest, reflecting the combined effect of variations in all components. In the example given in Table 2.8, the annual differences are not the result of genetic changes, but a reflection of variation in seasonal conditions. This makes it very difficult to compare individuals across years and to identify genetic gains simply by looking at flock average performance.

Table 2.8: Highest and lowest average annual performance for clean fleece weight and its component traits in a flock of Merino sheep randomly selected over a 20 year period. The difference between the two is expressed as a percentage of the lowest annual performance (B. Crook Unpubl. data).

Highest Lowest % diff.Clean fleece weight (kg) 3.8 1.5 153Body weight (kg) 42.2 27.4 54Wrinkle score 4.4 2.0 120Follicle density (no. per mm2) 60.9 43.6 40Staple length (cm) 10.7 6.9 55Fibre diameter (m) 23.7 20.1 18

2.7 Fibre diameterDiameter is defined as the length of a straight line through the centre of a circle or sphere and wool fibres are assumed to be circular. Mean fibre diameter is the average diameter measured in millionth of a metre. The unit is commonly called microns (m).

Statistically a mean is expressed as:X=å Xi / N

(where Xi is the diameter of the ith fibre, N is the total number of fibres measured).

The variability of the measurement is also important and will be covered later. However, not all wool fibres are circular in cross-section. Wool fibres are slightly elliptical as can be seen in Figure 2.4. While many fibres are circular in cross-section, the average ratio of the maximum width to the minimum width is 1.2:1, while a few fibres may reach 4:1. Modern fibre diameter testing equipment such as Projection Microscope, Airflow, Sirolan-Laserscan, or Optical Fibre Diameter Analyser (OFDA) does not measure the cross-section as viewed in Figure 2.4.



Figure 2.4: Cross-sections wool fibres show the variation ellipticity of the fibres (Tony Schlink 2006).

The measurement of fibre diameter is perhaps best considered to be "equivalent diameter”, i.e. no matter what the shape of the cross-section it can be converted to a circle and the diameter determined. As well as the non-circularity problem, the outer-surface of wool has scale edges that are about 0.7 microns above the fibre, therefore moving fractionally on or off a scale edges could change a measurement by 5%. These problems of lack of circularity and fibre unevenness are addressed by taking a sufficiently large number of measurements of fibres to determine a statistical mean fibre diameter for the wool sample.

2.8 The importance of fibre diameterMean fibre diameter is the most important raw wool property measured and accounts for 75 - 80% of the value of the top. Hence, mean fibre diameter is a significant determinant of the price of greasy wool.

Following are a number of reasons for the importance of fibre diameter. It is worth noting that it is one of the few raw wool parameters that remain virtually unchanged during processing. Diameter limits the yarn thickness (count) that can be spun from a given raw material. A yarn requires a minimum number of fibres in its cross section. Yarn thickness or linear density is limited by both mean diameter and the diameter distribution (Martindale’s theorem). For a given yarn count, various physical characteristics of the yarn such as bending rigidity and extension depend on the diameter of its constituent fibres, as well as the yarn twist and the spinning method. Yarns are woven or knitted into fabrics. Important fabric characteristics such as fabric weight, drape, handle, and comfort or “prickle” in next-to-skin wear (the mechanical effect of thick fibres poking into the skin) are dependent on the fibre diameter used.

While in most cases the finer the fibres the more attractive the material, there are two factors that work against the use of finer fibres. Sheep that grow fine wool generally grow less of it and the processing of finer wools is often difficult and more expensive. There is another important factor that governs the value of fibre diameter in the raw material and that is supply. In Australia, the world’s major supplier of apparel wool, the greater mass of wool is about 22 to 23 mm, with supply reducing as the diameter becomes finer or coarser.

2.9 The effect of fibre diameter on wool priceClean price increases as average fibre diameter declines. Thus there is a premium paid for finer wool types. In addition, there is an INCREASE in the price differential as fibre diameter DECREASES, i.e. the change from 20 m to 19 m is greater than the change from 25 m to 24 m. All prices for micron categories vary over the long term in value for each micron and in relation to micron categories as shown in Figure 2.5.



0

500

1000

1500

2000

2500

3000

3500

Dec-1979 May-1985 Nov-1990 May-1996 Oct-2001 Apr-2007

Woo

l pric

e (c

/kg)

Year

16.5

17

17.5

18

18.5

19

19.5

20

21

22

23

24

Figure 2.5: Long term prices for wool by micron categories (AWEX 2012).

2.10 Fibre diameter variationMeasures of fibre diameter variation are obtained from measurement of the fibre diameter distribution of a fibre sample. This involves the mini-coring of a fibre mass to obtain 2 mm snippets of fibre, of which approximately 2000 are then individually measured for mean fibre diameter using either the Laserscan (Charlton 1995) or OFDA100 (Baxter et al. 1992) systems or OFDA2000 using staples instead of using 2 mm snippets (Behrendt et al. 2002). The resultant distribution of fibre diameter is then used to derive the following parameters:

Mean fibre diameter (m) – the average diameter of snippets measured Standard deviation of diameter (SD, m) – this indicates how narrow or wide the distribution of

diameter is (ie. a measure of actual variation). Assuming normality, 68% of fibre diameters lay within 1 standard deviation either side of the mean diameter and 95% of fibre diameters lay within 2 standard deviations either side of the mean

Coefficient of variation of diameter (CV%) – this expresses the standard deviation as a percentage of the mean diameter. It is a measure of variation relative to the mean.

It is important to realise the difference between the two measures of variation. It is possible to have samples with the same spread in diameter but differing in CV% due to differences in mean diameter (Table 2.9, column 2). Also, it is possible to have samples similar for CV% but differing in actual spread of diameter (Table 2.9, column 3).


Notes – Lecture 2 – Fleece weight and its component traits and fibre diameterTable 2.9: The interaction between mean diameter, standard deviation of diameter (SD) and coefficient of variation of diameter (CV%) (Tony Schlink 2005).

The trends suggested in column 3 of Table 2.9 are those typically observed within most flocks. That is, as mean fibre diameter increases, so too does the standard deviation of diameter (Figure 2.6), such that CV% provides a measure of variation that is relatively independent of mean diameter.

Figure 2.6: Phenotypic relationship between mean diameter and standard deviation of diameter within a Merino flock (Crook et al. 1994).

2.11 Within-fleece gradients in diameter variationWithin-fleece gradients in mean diameter and the sources of variation in diameter were discussed in Section 2.4. In this section, the focus is on within-fleece gradients in diameter variation. In general, there is an anteroposterior increase in the standard deviation of diameter and a lesser increase dorso-ventrally. These gradients reflect those evident for mean fibre diameter, implying that gradients for CV% should be small. Thus the mid-side region is a suitable sampling site to measure diameter variation for flock testing purposes.

“Prickle” and “coarse edge”Some wool fabrics, when worn next to the skin, can evoke a “prickle” sensation. This results from the mechanical irritation of fibre ends on the skin surface, rather than an allergic reaction to wool (which only occurs for a very small proportion of the population). When fibre ends, protruding from the fabric surface, come in contact with the skin, there are two possible outcomes. The fibre end can either deflect away from the skin surface, or it can press into the skin surface. The latter scenario activates pain receptors in the skin, which are interpreted as “prickle”. Importantly, the main determinant of whether the fibre end deflects or not is the diameter of the fibre. Thus “prickle” is not a wool-specific phenomenon, but is more closely associated with wool due to comparative diameters of wool, cotton and synthetics.

Research has shown that “prickle” arises when a fabric to be worn next to the skin, has around 5% or more of fibres exceeding 30 m. These coarser fibres show less tendency to deflect away from the skin surface. This proportion of coarse fibres is commonly referred to as the “coarse edge” of the diameter distribution. It should be noted, though, that many factors such as fabric construction and finishing techniques influence the actual threshold of coarse fibre required to generate “prickle”.

As the average diameter of the flock increases, so too does the percentage of sheep within the flock that have 5% or more of fibres exceeding 30 m (Figure 2.7). Once the flock average diameter exceeds 21 m (approx.), the percentage of sheep in the flock with “coarse edge” of 5% or more increases rapidly

2-10 ________________________________________________WOOL412/512 Sheep Production© 2013 The Australian Wool Education Trust licensee for educational activities University of New England

Mean diameter (m)

CV% when SD=3.5m

SD when CV=20%

19 18.4 3.8

22 16.0 4.4

25 14.0 5.0


and exponentially. Likewise, within a flock, the percentage of fibres in the fleece exceeding 30 m rapidly increases once the fleece diameter exceeds 21 microns (Figure 2.8). Thus the higher the diameter of the fleece or the flock, the greater is the likelihood of high “coarse edge” and is usually reported as comfort factor, the percentage of wool fibres with a fibre diameter less than 30 microns.

Figure 2.7: Flock average diameter and the percentage of ewes with 5% exceeding 30m (B. Crook Unpubl. data).

Figure 2.8: Within-flock association between mid-side mean diameter and the percentage of fibres exceeding 30m, in a fine wool flock (top) and a broad wool flock (bottom) (B. Crook Unpubl. data).



Micron “blow-out”As sheep age, there is a general trend for average diameter to increase. But some sheep increase faster than the average, whereas some show slower change with age. Micron “blow-out” refers to a change in diameter with age, at a rate faster than the flock average rate. Another term sometimes used is micron “stability”, generally expressed as a difference in diameter between two ages (e.g. diameter measured at 10 months and 16 months).

There is a perception within the industry that high diameter variation at a young age is an indicator of micron “blow-out” at a later age. Research results do not, however, support this (Table 2.10). In one study, hoggets with higher than average diameter variation were actually more stable in diameter as they aged.

Table 2.10: Phenotypic correlations between mid-side diameter distribution measurements and micron “blow-out” (Taylor and Atkins 1992 and Ponzoni et al. 1995).

Taylor and Atkins (1992)

Ponzoni et al. (1995)

Mean diameter -0.30 -0.24

SD of diameter -0.20 0.05

CV of diameter 0.0 0.08

ReadingsThe following readings are available on web learning management systems1. Dun, R.B. 1958, ‘The influence of selection and plane of nutrition on the components of

fleece weight in Merino sheep’, Australian Journal of Agricultural Research, vol. 9, pp. 802-818.

2. Leroy Johnson, C. and Svend-Aage, L. 1978, ‘Clean wool determination of individual fleeces’, Journal of Animal Science, vol. 47(1), pp. 41-45.

3. Mortimer, S.I. and Atkins, K.D. 1993, ‘Genetic evaluation of production traits between and within flocks of Merino sheep. II. component traits of the hogget fleece’, Australian Journal of Agricultural Research, vol. 44, pp. 1523 -1539.

4. Thornberry, K.J. and Atkins, K.D. 1984, ‘Variation in Non-Wool Components of the Greasy Fleece Over the Body of Merino Sheep’, Australian Journal of Experimental Agriculture: Animal Husbandry, vol. 24, pp. 72-76.

5. Turner, H.N. 1958, ‘Relationships Among Clean Wool Weight and its Components. I. Changes in Clean Wool Weight Related to Changes in the Components’, Australian Journal of Agricultural Research, vol. 9, pp. 521-552.

ReferencesAdvanced Breeding Services, 2003, Wool Price for 15 to 24 micron indicators – 1975 to 2003. NSW,

DPI, Orange, NSW.AWEX. 2012. Micron price indicators courtesy of Lionel Plunkett, AWEX.Baxter, B.P., Brims, M.A. and Teasdale, D.C. 1992, 'The optical fibre diameter analyser (OFDA), new

technology for the wool industry'. Wool Technology and Sheep Breeding, vol. 40, issue 4, pp. 131-134.

Behrendt, R., Konstantinov, K., Brien, F., Ferguson, M. and Gloag, C. 2002, 'A comparison of estimates of mean fibre diameter, variation in fibre diameter and fibre curvature between OFDA 2000 and conventional laboratory-based fibre testing', Wool Technology and Sheep Breeding, vol. 50, issue 4, pp. 780-786.

Brown, G.H. and Turner, H.N. 1968, ‘Corrigendum - Response to selection in Australian Merino sheep. II. Estimates of phenotypic and genetic parameters for some production traits in Merino ewes and an analysis of the possible effects of selection on them’, Australian Journal of Agricultural Research, vol. 19, pp. 303-322.



Carter, H.B. 1943, ‘Studies on the biology of the skin and fleece of sheep. 3. Notes on the arrangement, nomenclature and variation of skin folds and wrinkles in the Merino’, Council Sci. Indust. Res. Bull. 164.

Charlton, D. 1995, 'Sirolan-Lasarscan. A review of its development, performance and application', Wool Technology and Sheep Breeding, vol. 43, issue 3, pp. 212228.

Crook, B.J., Piper, L.R. and Mayo, O. 1994, 'Phenotypic association between fibre diameter variability and greasy wool staple characteristics within Peppin Merino Stud flocks. Wool Technology and Sheep Breeding, vol. 42, issue 4, pp. 304-318.

Dun, R.B. 1958, ‘The influence of selection and plane of nutrition on the components of fleece weight in Merino sheep’, Australian Journal of Agricultural Research, vol. 9, pp. 802-818.

Dunlop, A.A. and McMahon, P.R. 1974, ‘The relative importance of sources of variation in fibre diameter for Australian Merino sheep’, Australian Journal of Agricultural Research, vol. 25, pp. 167-181.

Gregory, I. 1982, ‘Genetic studies of South Australian Merino sheep. 4. Genetic, phenotypic and environmental correlations between various wool and body traits’, Australian Journal of Agricultural Research, vol. 33, pp. 363-373.

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